Intercomparison Procedures in the Dosmetry of And

INTERCOMPARISON PROCEDURES DOSMETRE TH N I F YO HIGH-ENERGY X-RAY AND ELECTRON BEAMS

REPOR ADVISORN A F TO Y GROUP MEETING ORGANIZED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY AND HELD IN VIENNA 2-6 APRIL 1979

A TECHNICAL DOCUMENT ISSUEE TH Y DB INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1981 The IAEA does not maintain stocks of reports in this series. However, microfiche copies of these reports can be obtained from

IN IS Microfiche Clearinghouse International Atomic Energy Agency Wagramerstrasse5 0 10 P.Ox Bo . A-1400 Vienna, Austria on prepayment of Austrian Schillings 25.50 or against one IAEA microfiche service coupon to the value of US S2.00. CONTENTS

REPORT AND RECOMMENDATIONS OF THE ADVISORY GROUP

Repor recommendationd an t Advisore th f so y Group...... 7 . APPENDI . I XIAEA/WH O postal dose intercomparison (TLD) for high energy X-ray therapy. Instruction sheet...... 7 1 . APPENDI . XII IAEA/WH O postal dose intercomparison (TLD) for high energy X-ray therapy. Data sheet...... 21

EXPERIENCE WITH AND THE NEED FOR DOSE INTERCOMPARISONS

The IAEA/WHO thermoluminescent dosimetry intercomparison used for the improvemen clinicaf o t l dosimetry ...... 7 2 . N.T. Racoveanu A surve f clinicallo y y applied dosimetry (Summary e reporth n o t IAEA/WHO postal dose intercomparison of cobalt-60 telecurie units with TLD) ...... 3 3 . Seelenta. W g Dose intercomparison programm Regionae th f o e l Reference Centre of Argentina ...... 45 R. Gonzalez, M.S. de Fernandez Gianotti Experience in intercomparison at an SSDL for orthovoltage and high energy beams ...... 51 G. Subrahmanian, I.S. Sundara Rao Bureau of Radiological Health Activities in Dose Delivery Surveys.. 57 R. Morton Status of radiation therapy in Nigeria and problems of accurate dosimetry ...... 59 A.O. Fregene

DOSIMETRY WITH FERROUS SULPHATE SOLUTIONS, TLD AND IONIZATION CHAMBERS e ferrouth f o s e sulphatUs e dosimete s transfea r r instrument for calibrating clinical dosimeters ...... 5 6 . J.P. Simoen Chartier. ,M Page. ,L s Measurement assurance studie high-energf o s y electro d photoan n n dosimetr radiation-therapn i y y applications...... 5 7 . Ehrlich. M , G.G. Soares

resultA e revieth f wo s obtaine NPL/PTe th y b dB Fricke dosemeter calibration servic German i e n radiological centres ...... 9 8 . . FeisH t FeSOf o somn e i ,us e e practicaTh l aspect high-energf o s y photon and electron dosimetry ...... 95 Wambersie. A Prignot. ,M Dutrei. ,A x Postal dose intercomparison for high-energy X-rays and electrons witD ...... TL h l Il . B.E. Bjärngard, B.—I. Rüden, P.J. Biggs, A.L. Boyer, K.A. Johansson, K.R. Kase Absorbed dose determination with ionization chambers in photon and electron beams ...... 9 12 . K.A. Johansson, L.O. Mattsson High energy radiation dosimetry and cavity theory - a re- examination ...... 7 13 . A.O. Fregene

ANNEX

Procedure Externaln si " Radiation Therapy Dosimetry with 5 Electro14 d nan Photon Beams with Maximum V EnergieMe 0 5 sd betweean V Me 1 n Recommendations by the Nordic Association of Clinical Physicists Reproduced witkine th hd permissio Actf o n a Radiologica

L/is't of participants 169 REPORT AND RECOMMENDATIONS OF THE ADVISORY GROUP

1. Introduction

radiotherapf o m Theai achievo t s besye i eth t tumour control with a minimum of radiation-induced complications in critical normal tissues. The implementatio thif no s object depends upon various factorse Th . present report, however, concerns itself specifically with the improvement of dosimetry and its uniformity.

All present biological and clinical evidence indicates that at a critical absorbed dose level ,differenca absorben ei d dos lesf eo s thaproduc$ 10 n e difference biologican si tumouls a effectr rfa s sa contro normad lan l tissue reaction concernee . sar 2] , d[l

A possible procedure for achieving the goal of improving dosimetry is to send an expert to the various radiotherapy centres and have an on-the- spot dose determination. Anotheachievinf o y rwa g this woulo t e db « greatly enlarge educational programme trainine th r medicasfo f g o l physicists and other persons responsibl radiatior efo n dosimetr thein yi centresn row . A third procedure is to make use of a mailed dose meter for the determination of absorbed dose.

A postal dose intercomparison programme of absorbed dose for Co y-rays was initiate IAEe continueds 1966n th ha Ai y d b large,a an n ,o r scale, since 1970 with WHO collaboration. Thermoluminescence dosimetry was used for this study. In 19?6, an Advisory Group to the IAEA recommended to extend the same technique for dose intercomparison to the field of orthovoltage X-rays.

présene Th t report deals witextensioe hth postae th f lno absorbed dose intercomparison programm high-energo et y photo electrod nan n beams.

The need for accurate dosimetry in this field is well recognized and results from the proliferation of these machines. The increased use of high-energy photo electrod nan n beams means thae earltth y indication oincorrecn fa t absorbed dos acutn shows a ea y enb skin reactios ni eliminated. Moreover reducee ,th d skin reaction allow higher sfo r tumour doses. In this situation the accuracy of the dosimetry is revealed only in late radiation effects with a latent period of at least several •- months. Therefor absorbee eth d dose give high-energy nb y photod nan electron beams mus wele tb l established. 2. Objectives

The objective plannee th f so d postal dose intercoraparison programme are simila thoso rt e formulate formea n di r IAEA report (TR 182). SNo . creato T ) greateea (a r awarenes neee correcr th dfo f so t dosimetry in radiation therapy. (b) To compare and improve the accuracy of the clinical delivery of the radiation dose. (c) To improve dosimetric consistency within and among radiation therapy centres. o identifT ) (d ysourcee th som deliver e f erroeo f se th o th n ri f yo target absorbed dose as well as methods by which these may be corrected.

3. Spécifia aims

presene th f o t m programmai e exteno t Th postae s ei dth l dose intercomparison programme initiated by the IAEA and the WHO to high-energy radiation emitted by betatrons, linear accelerators, and other similar equipment, i.e.:

- X-ray maximuf so m energV Me 20tf yo 0 5 o - Electrons with nominal energy of 2 to 50 MeV

The dosimeters which nowo t ,p ,u hav e been propose used sucr dan dfo h postal intercomparisons are the PeSO, chemical dosimeter and the thermoluminescence dosimeter. Their respective advantage disadvantaged san e sar discussed here, taking into account tneir general merits as well as practical considerations.

r thiFo s intercompariso dosimetrie choice th nth f o e c metno wels da l technicae th f o s la procedures shoul provido t suce db s ha determinatioea n of absorbed dose witr uncertaintn .a lesf yo s. tha5$ n+

As for the other energy ranges already investigated, the planned intercomparison programme snould help in the assessment of the reasons for significant discrepancies sucf ,i h discrepancies occur.

4. Methods

4.1. General

methodo Tw s that coul usee db specifie meeo t dth t c aimthermoe sar - luminescence and ferrous sulphate dosimetry. 4»2. Thermoluminescence Dosimeters

4«2.1. Lithium Fluoride Powder

The ongoing IAEA/WHO postal dose intercomparison programme is based powderP ocharacteristics Li nsyste e it Th .d man s have been described elsewhere [3»4]> The reproducibility of the dosimeters irradiated in beamo C particularn ,i a bees $ ,ha n95 evaluatee 1,5+ th s i $t a d dan confidence level. This figure has been obtained by dividing the LiP powder eacn ,i h dosimeter int equao5 l part takind san averag e gth f eo these readings.

Preliminary experiments indicat energy-dependence eth systee th f meo for photons with a maximum energy of 4 to 25 MeV is less than 2$ [5].

Data frosame mth e experimental study indicate thaenerge tth y dependence of the system for high-energy electrons is greater than that for high-energy X-rays (i.e. 10$ in the range from 4 to 20 MeV).

4.2.2. Pressed Lithium Fluoride Thermoluminescence Dosimeters (TLD "chips")

Pressed LiP TLD chips have been used without build-up in surveys of dose delivery during clinical radiographie procedures sealen [6,7i d ]dan glass extensivn bulba r sfo e one-time teletherap o surveC f yo y dosimetry [8,9,10]. pressee th n advantage i d th LiD fors PTL mha powdeD eTL ovefasteP f ro rLi r reproducible readou equipmenn ti t lending itself readil partiao yt l automation of dosimeter handling. A disadvantage is the need for either individual dosimeter calibration between successive mailings or for selection and calibration of dosimeter comparablf so e respons identicao et l irradiation.

The relative standard deviation from the mean response of individual cnips varies somewhat from dosimeter to dosimeter. On the average, at the 95$ confidence interval for the mean response of an individual bare dosimeter chip irradiated 9 times at one given level and read in a hot-nitrogen reader it was about +1,0 percent; that for an individual sealed bulb in whicf, the two enclosed chips are permanently in contact with an electrically

r.eatable metal strip was about +_ Of6 percent. When the quantity of dosimeters thousandse handleth n i s becomedi t ,i s cumbersom keeo e t wit p pu h dosimeter identity. In tnis case, a batch calibration is preferable. If one selects a batch of dosimeters of which, on the average, the individual dosimeter readings var abouy yb percent3 _ t+ obtaine ,on measa n response fro9 m identically irradiated dosimeter percen5 9 e whicr th ts fo t hconfidenca e interva standare lth d deviatio percent5 abous ni 1, t+ . 4-3- Ferrous Sulphate Dosimeter (Fricke Dosimeter)

Tte ferrous sulphate dosimeter is extensively used by National Standardizing Laboratorie calibratior sfo intercomparisonr fo d nan , both by postal service 14], 13 ,, s Sinc12 [ll, eIAEe 1965th A , als carries oha d out postal intercomparisons based on this method [15]-

The following advantages of the ferrous sulphate technique are particularly applicable here:

) 1 High precisio $ confidencn95 (withie th t a e0,5n+ $level accuracd )an y (within £ 2% for Co, better than within + 5$ f°r "the radiation qualities under consideration). 2) Change in the energy response of less than 1% for the radiation qualities under consideration. ) 3 Approximate water equivalence. ) 4 Dose rate independent response ovedose rth e rate rang clinican i e e lus 14], .[1213 ,

However, acceptable precision can only be obtained if particular care is taken in the preparation, handling and evaluation of this dosimetric technique. Thus, from a practical point of view, certain disadvantages must be taken into account : 1) The method is relatively laborious and expensive. 2) Since the ferrous sulphate solution is acid and poisonous, postal regulation mann si y countries prohibi conveyancs it t ordinary eb y mail. 3) The reliability of the solution might decrease when the time between preparatio evaluatiod nan n exceed monthsw fe sa . 4) Higher absorbed doses than those used in clinical application have to be delivered. energn A y) 5 dependent perturbation facto introduces i r glase th sy db container.

4.4« Recommended Procedure

It is recommended that the established Co postal dose intercomparison P powdeLi y extendee rb b higr.-energo dt y wate n X-raysi m rc 0 deptA .1 f ho capsulee th r recommendes fo si thesr dfo e irradiations. Correctionr sfo measured light versus absorbed dose givequalite wateth o nt r yrfo under consideratio nominae basee th b nn y do musl ma mad e energytd b ean .

It is recommended that the absorbed dose intercomparison for high- energy electrons also is by LiP powder. To meet the accuracy required , correction for the energy dependence has to be made. This correction can be made on the basis of nominal energy, supplemented by information derived from depth dose curves provide participante th y db .

10 For electron beams of energy lower than 8 MeV, experimental diffi- cultie determininn si dose gth e accurately witdosimeterF Li h s wil- lin disturbancee th creaso t fluence e th e du f so e dosimetecausee th y db r holders anit d additionn I . accurate ,th e positionin dosimetee th f go r become characteristice sth cruciao t e deptle du th hf so dos e curves energiesw alo t thesr Fo . e reasons unlikels i t ,i y thauncertainte th t y of the dose evaluation of + 5% can be achieved for energies <8 MeV. However, since electron beam thesf so e energie usee sar d clinicalld yan since their dosimetry is difficult, an intercomparison would be valuable even wit uncertaintn ha e rangth _f +n eo i y1C$ .

plannee th r dFo IAEA/WHO postal dose intercomparison depte ,th f ho irradiatio electror nfo n beanswil establishee lb d afte completioe rth f no experimentae th l study mentione action di - 5 n

4«5- Actions in Case of Intercomparison Discrepancies

All participants will be informed of their results and in particular of the deviation between the quoted absorbed dose and the dose determined by the IAEA. It is generally recognized that a deviation of up to jh 5$ in dose is within the presently accepted requirements for effective radiotherapy.

r largeFo r deviations importans i participane t th ,i r tfo investigato t e causee attempo t th d o improvt san s dosimetrhi e y procedure.

deviationr Fo s above recommendes i 10J& t i , d t..at IAEA/WHO take eth following measures: 1. Inform the participant immediately. . 2 Advis participane eth participato t nexe th t n planneei d intercomparison. . 3 Attemp determino t probable th e e observee reasonth r sfo d discrepancy froanalysie datmth e th a f so shee providd an t e this informatio participante th o nt , together witguidee th copha f -yo lines compile thir dfo s purpose (see Appendi- x5)

For deviations greater than 15%, it is recommended that the following additional measures be taken by IAEA/WHO: 1. Send a letter immediately to the radiotherapist in charge and/or the phycisist who carried out the intercomparison, urging him to repeat the dosimetry and check all computations of absorbed dose. Tr.e contents of this letter should be considered strictly confidential, inasmuch as it may involve the treatment of patients.

2. If the preceding step confirms the previous results, recommend to to the participant to have his dosimeter calibrated immediately.

11 5- General Recommendations

While thernecessita s ei dosimetnr yfo c Intel-comparisol al r fo n energie modalitied san s use radiation di n therapy especian thera s i e l urgency to perfor n intercompansoa m dosimetrf no high-energr fo y y X-ra d electroyan n equipment. This necessit brougr.s yi t rapi e abouth dy tb proliferatio f o n this type of equipment and the possibility of serious dosimetry errors due to the complexity of the medical accelerators and trie dosimetric procedures. high-energr Fo y X-ray rise accidenf sth ko overdoseo t e du t increases si d reducee th y b d early skin reactions. Thu radiotherapise sth inadvertentln tca y deliver high doses without producing visible severe reactions.

Therefore, this Advisory Group recommends ï

1) Users of high-energy X-ray and electron machines should be encouraged to conduct radiation therapy only witparticipatioe htn qualia f no - fied medical physicist; internationan A ) 2 l postal absorbed dose intercompanson programmf eo high-energy photon d electronsan s shoul initiatee db IAEA/WHy db O earliese th t a t possible followee datb o et similay db r SSDL programmes. The following studies should be included: a) A pilot study should be conducted for high-energy X-rays. A sufficieit number of institutions in various countries and witn different macnines shoul includede db . b) For hign-energy electrons, the experimental study of precision d energan y dependencF systeLi e m th shoulf eo continuee db y db IAEA. Measurements with FeSO. should be included. It is recommended well-establishee th f o thae on t d centers already carryint gou FeSO. dosimetry provide this service. importance th n vie I IAEA/WHe f o w) th c f o e O intercomparison service, it is recommended that tne IAEA take measures to make this service availabl widea o et r international community, maintainine gth present high-leve performancef lo .

12 APPENDIX

IHTERCOHPARISON OF ORTHOVOLTAGE THERAPY DOSIKETRY

repore th reconunendationf n to I Advisorn a f so y Group Meeting, organized "by the International Atomic Energy Agency and held in Vienna, 6-10 December 1976, a pilot study of the X-ray postal dose intercomparison technique for orthovoltage therapy was requested. The pilot study was conducted in the summer of 1977 sna. the results were reported [16].

The conclusion piloe th tf s o study were summaryn ,i : a) The external filter technique for determining HVL is practical ovequalite th r y rang interesf eo necessars i e d th tan r yfo purpose of correcting the TLD signal for the energy dependence of LiP. techniquD TL P Li ee provideTh ) b s sufficient precisiod nan reliability and meets the requirements of the Advisory Group (1976) that "the accurac dose th e f determinatioyo n should be better than £ 10$ and preferably £ 5$..

197e Th 9 Advisory Group confirms these conclusion recommendd san s that the IAEA/WHO and the SSDL's conduct intercomparisons in the orthovoltage energy range using this technique, adhering to the conclusions piloe ofth trecommendatione studth d yan 197e th 6f so Advisor y Group.

13 REFERENCES

[I] Lanzl. L.H..; Why is a high accuracy needed in Dosimetry? Inter- comparison Procedures in the Dosimetry of photon radiation (Techn. Rep. Ser. 182), IAEA, Vienna (1970), 8l.

] Turesson[2 Notterd an Ski; . . ,I ,G n reactio biologicaa s na l paramete contror fo r differenf o l t dose schedule correctionp ga d san . Acta Radiol. Ther. Phys. Biol (1976)5 .1 , 162, [3j Eisenlohr, H.H., Haider, J.G. and Rüden, B.—I«; International Postal Dose Intercomparison, Fifth Int. Gonf. on Lum. Dosimetry, Sao Paulo (1977), 350. [4] Bjarngard, B.E., Rüden, B.-I., Bisenlohr, H.H., Girzikowsky, R. d Raideran Evaluatio; . ,J e 197th 7f o n IAEA Pilot Studf yo Postal Dose Intercomparison (TLD Orthovoltagr )fo e X-ray Therapy. Nationa d Internationalan l Standardizatio Radiatiof o n n Dosimetry Vol Vienna, 1 . j IAEA, 319. ] Bjarngard[5 , B.E Rüdend .an , B.-I.; IAEA's Postal Dose Intercomparison (TLD) System for High Energy X-rays and Electrons, this publication, p.111 ] Crabtree[6 , C.L. Jamesond ,an Denta; 5. , l Exposure Normalization Technique "DENT" Instruction Kanual, HEW Publication (PDA) 76-8042 published by US Department of Health, Education, and Welfare,'Pood and Drug Administration, Bureau of Radiological Health, Rockville, Maryland. ] Jans[7 , R.G.;A Federal/State quality assurance progra mammographyn mi , In Breast Carcinoma, the Radiologist's Expanded View, Edited by Wende Logan, p.121. New York, N.Y. John Wiley and Sons, Inc., 1977. [8] Ehrlich, K...,. Welter, G.L.; Nationwide Survey of Co-60 Teletherapy Dosimetry, J. Res., National Bureau of Standards—A. Phys. and Chem., 80A, 663 (1976). [9] Soares, G.G., Ehrlich, L:.; Nationwide Survey of Co-60 Teletherapy Dosimetry, NBS Technical Note 978, US Department of Commerce (1978). [10] Thompson, D.L., Kearly, F.B., Uyckoff, E.O., Gitlin, J.N.; Nationwide Surve Co-6f yo 0 Teletherapy: Final Report, Techn. Rep., Sept. 1979, publishe DepartmenS U y db Healthf o t , Education Welfared ,an , Food d Drug-Administrationan , Burea Radiologicaf uo l Health, Rockville, Maryland. [II] Ehrlich, H. and Scares, G.G.; Measurement assurance studies of high- energy electron and photon dosimetry in radiation therapy applications, this publication. 75 . p ,

[12] Peist, H.; A review of the results obtained by the NPL/PTB Fricke dosimeter calibration service in German radiological centers, this publication, p. 89.

14 [13] Ellis, S.G.; The dissemination of absorbed dose standards by chemical dosimetr yFrickf o mechanis e eus dosimeterd man , Ionizing Radiation Metrology, ed. by E. Casnati (1977). [14] Simoen, J.-P,. ferroue th , f Chartiero s e sulPagesd Us an ; -. ,L. M phate dosimete transfes ra r instrumen calibratinr tfo g clinical dosimeters, this publication. 65 . ,p [15] Sanielevicid Naglan . ,J Dosisvergleichsmessunge; ,A. hochr fü n - energetische Elektrone Eisensulfat-Dosimetert nni , Strahlentherapie, 133 (1967), 36 x [l6] B.lärngard,, B.E. and Rüden, B..-I..; Report of Consultants' meeting to evaluat 197e eth 7 pilot stud postaf yo l dose intereomparison (Till) for orthovoltage-X-ray therapy, Techn. Rep. Ser. 182, IAEA, Vienna (1978), p.155«

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15 APPENDII X

IAEA/MHO POSTAL DOSS IMTE3COMPASISOÎT (TLP) FOR HICK ENERGY" X-RAY THERAPY

INSTRUCTION SHEET

ATTENTION; to obtain appropriate results IT IS ESSENTIAL TO EXPOS RETURD EAN N THESE DOSIMETER CASO N 3N I SLATE R THAN

to the address given in the covering letter. Exceeding the time limit entails uncertainties in the results. Such dosimeter evey n ma s e disregarded havb o t e .

If you are unable to carry out the irradiation before e datth e indicated above, t beforRETURse e e th eth N deadline, markin t gi tf£JH5XPQSS3" .

WARNING.: Capsules rar.ist never be exposed to heat (e.--;. sunshine), nor stored in a place where accidental exposure to ionizing radiation cannot be excluded.

TBOH-TTCAL INSTRUCTIONS :

Please read all the following instructions carefully before you start irradiating the cspcules. Aloo' complex e DATth e A SHEET carefully; onlyn a the s i n evaluatio e resultth appropriatf d no san e advice possible.

A. Preparatio e holdeth v;ate d f o nan r r phantom

1. The parts of the holder are shown in Piß. \. There is a long lucite tube with a hole in it across its long axis, attached to a (red) disc at one end. The disc has three holes. Also in! e showar I Fign . three (red) sticks e fittesticke b Th n . dca s holdee t^ dise intd s holee thei rth oan th n f i s read r usefo y . (Look s showa s n Fir;i n , ii.).

17 (Caution: the parts of ihe holder are to be handled carefully s otherwisa e deformation will resurlt).

. 2 Piec waterprooea f containe ry irateria madan f o e l available and. having a minimum length, width and height of 30 cm each, in a vertical X-ra^ beam. Alig containee centee th th n f o r r witcentrae th h beamle axith .f so

. 3 Plac holdee eth r intcontainee th o y thaplactie n sucwa i r th t a h c tube is aligned with the central axis of the b.eam. 4. Fill the container with water exactly to the level of the top end holdere th f o . Check that the plastic tube is completely filled with water-and, in the case the TLD capsule is tu be inserted while the holder watere th n ,i checs i k also thaalignmens cha.n/^edt it no s ha t .

. B ExposincapsuleF Li e gth s

e insertioTh D capsule TL performee b f o ny sma d befor holdee eth r is placed intcontainee th o r afte fule th rl alignmen holdee th f ro t wit X-rae th h y beam decisioe .Th usere th lefs i n.o t fielm c yout 0 a d1 rx norma0 1 a le sourcUs surfaco . t e1 e distance (BSD r sourc)(o centre-of-capsulo et e distancf ei normallu yo isocentrin a e yus c set-up).

2. Insert one of the three LiP capsules to be exposed by you into the hole at the upper part of the tube of the holder. Insert first the capsule th s showf botto o avoi o (a e Pigt n d ni ) en dm. iv openin g by accident. Place the capsule so that it shows extends equally on deptm botc 0 h hcapsul1 e tube sidet th th a e w f s so (Pigei No . .v) in water and ready for exposure (Pig. iii). Recheok alignment, water level and distance.

3» Calculat irradiatioe eth n time accordin methoe th o dgt u useyo y db in your daily practice ("Guideline calculatinr sfo g absorbed dose ...", ). Under these conditions irradiate one of the three LiP capsules to give an absorbed dose of 2 Gy (200 rad).

. 4 Remov capsule th e e froholdee th m pushiny rb g agains bottoe tth d en m of the capsule (Pig. vi).

5. Repeat procedure from 2 to 4 at the same machine with the same arrangemen othee capsuleso th r eac tw rtfo f ho exposee b o ,r t fo d the same time.

18 6. The capsule with white stopper is for the purpose of checking environmental influence capsulee th n so s during transpord tan storag irradiatede b d mus t ean tno t should;i , however e store,b d together wit otherse hth .

7. Throughout all procedures, handle the capsules very carefully to prevent opening and loss of powder.

C. Completion of the Data Sheet

Completio. 1 date th a f no shee essentias i tevaluatioe th r fo l f no dosimeter readings; dosimeters withou witr to h incomplete data sheet evaluatede sb wil t lno . Give more informatio additionan a n no l wisho s sheetu .yo f ,i

Indicat. 2 e irrelevant question y "NAapplicablest b No " = .

3. In the data sheet use has been made of the new SI units. The old unit givee sar parenthesn i n participantf .I s already employ thee th m givee b dat thesn y i n ama e units.

THANK YOU FOR HAVING BEAD AND FOLLOWED THESE INSTRUCTIONS

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19 APPENDII I X

IAFA/HHO POSTAL DOSE INT5RCOMPARISON (TLD) FOR HIGH-ENERGY X-RAY THERAPY

DATA SHEET

''Please use BLOCK LETTERS or typewriter, particularl r n=une yfo addressesd an s )

>'=•"» of institution ... Addres f institutioo s n

Form completed by ...... (name) (position) (date)

Signature ......

Previous participation in the IAEA/WHO Cobalt-eO TLD intercomparison 1 [ date...... s Ye ] N[ o . e IAEA/WHth n i r Oo orthovoltage X-raintercomparisoD yTL n No [] Yes [] date...... or in the IAEA/WHO high-energy X-ray TLD intercomparison ] [ date...... s Ye ] N[ o .

It is of great importance for the evaluation that all information requeste date th a n sheei d filles i t . in d The data sheet cannot cove possibll ral e measurement proceduresa f .I participant uses a procedure not covered "by the data sheet, he is rerjested to give full details of his method on pasre 4.

A. Specificatio acceleratoe th f no r

1. Type and model of accelerator Dat. 2 installatiof eo n Nomina. 3 l energ irradiatioe yth use r dfo n of the IAEA dosemeters

21 Detail Beaf so m dosimetry

Specification of dosemeter Typ) a doBemetef eo r (ionization chamber) Seria) b l dosemetenumbee th n ro r Dat) c calibratiof eo n Calibratin) d g laboratory Calibratio) e n facto Co-6r rfo 0 f) At which temperature and pressure calibratioe ith s n factor valid .mmHg g) Check source reference reading at tim calibratiof eo n h) Radionuclide in check source

Actual condition time f th eo t sa the calibration of the beam. a) Type of monitor chamber in the accelerator pressure Ar ) temperatud b ean r corrections applied to the monitor reading Chec) c k source reading d) Check source reading corrected for decay e) Dosemeter reading Temperatur) f phanton i e m during calibratio) C ( n g) Air pressure in the phantom during- calibration (mmHg) h) Correction factor for temperature and air pressure i) Or correction factor derived from check source reading Correctio) j n facto recombinatior rfo e th n i n dosemeter. Pactor(s) k ) useconvertinr fo d g dosemeter reading to absorbed dose to water Accelerato) l r dose monitor setting m) Medium for measurement

22 3. Beam dosimetry

1. Date for calibration of the beam . 2 Sourc detectoo et r distance (cm) 3. Source to surface of the medium distance (cm) a. Field size at the surface of the medium detectoe th t a rr ) o positioCT x m (c n 5. Beam calibration factor for the accelerator; a) absorbed dose per monitor unit (Gy/mon^ depte th phanton i ht a (cmf mo ) b )

C. LiF-oapsule irradiation

Give values for only those factors th=t are used by you for calculation below. Write NA against whichever is not applicable. In your computation of absorbed dose to perturbatioe watercorrect th no r o ,d tfo n introduced by the LiF-capsule. 1. Date of irradiation . 2 Sourc wateo et r surface distance (SSD)(cm) 3. Field size at the water- surface or at the ) positio cm capsulF x Li m f no (c e . A Dose monitor setting 5. Absorbed dose delivered to water at the irradiation of LiF capsules (Gy) casn I e your calibration t identicadeptno s i h l wite hth depth at which the LiP capsule is irradiated '10 cm) please /riv followine th e g additional information. 6. Depth of calibration (cm) 7. Percentage deoth dose at calibration denth 8« Percentage depth dose at a death of 10 cm

23 . D Please giv arrive u figure detain yo ei th w t eldho a given in B.5 n cas.(i eclearlt thino s si y enough describee th y db data requested).

E. Pull details of measurement procedures if not covered by this data sheet (see pag. el)

P. If you have suggestions to improve this intercoraparison, please give details.

24 -r, i rt<- | TLI>

na 55 0 SAO Ti-a T- i l \ •fifi. P ' l t / r. \ I ôcm lOc-m W

Vl m

'} OSi-( i -no, f

25 Next page(s) left blank THE IAEA/WHO THERMO LUMINESCENT DOSIMETRY INTERCOMPARISON USED FOR THE IMPROVEMENT OF CLINICAL DOSIMETRY

N.T. RACOVEANU Radiation Medicine, World Health Organization, Geneva

Introduction

A number of papers have already presented .-UK! analysed t-lie IAEA/WHO TLD postal dose intorcompariso r Co-6fo n 1etlierapy e 0t . Mos f theso t e have been lie-votee methodologth o e resultt d th r o ys obtained without considerine us e th g of these result o improvt s e clinical dosimetr n centrei y s where this beeha s n shown necessary from the TLD results.

The present paper is based on the experience of the author in one of the Regional Office O wherWH n attempf a e o tins us -o TI/t t J result o improvt s e clinical dosimetry was made during the last five years.

Pa-suits of the TLD intcrcomparison in the Eastern Mediterranean Region of WHO

The results discussed here wore obtained from 23 radiotherapy departments located in universities or spocia1izcd hospitals in 12 countries of the Tastern Mediterranean Region. All the given data represent dose and not dose ratd weran e e obtained during 1971-1978 (TLD batches II-XXII) e resultTh . s are presented in Table I by country and radiotherapy department.

Of the 104 measurements undertaken in the 23 departments 53.9% did not exceed ^_5.0Z deviation froe giveth m n dose-1, whic s considerei h n acceptabla d e limit for clinical dosimetry. The remaining 46.1™ of i»oasurenients exceeded j|;5.1% and therefore fall into the category of unacceptable precision for clinical dosimetry. Of this latter group 25.9% exceeded ^10.IZ and of this 2.97. exceeded +20.1% deviation, as can be seen from the last line in Table I.

n observatioA s alswa n o made concernin e ratith gf positivo o o negativt e e deviations; positive deviations meaning doses given which exceeded the given vjlu d negativan e e deviations those administere f leso d s thae giveth n n value. All deviations in the range of -"-5.0 - ^10.07, are equally distributed in the positiv d negativan e e areas e ratith , f positivo o negativt a e being justa little ovee unity th rf O deviation. s greater than _+10.0 a %large r numbee ar r found to be negative, the negative/positive ratio beinr 1.7.

JLD results trends

Data from 1(> radiotherapy departments have been set out to show their chronologi cal evolution so that it r.iny be seen whether the 1 LI) interconiparison h.-id an influence on the precision of the clinical dosi:r.otry. The departments have been split into three categories according to their TLD results: !) radiotherapy departments with good results (graph 1); 2) radiotherapy departments with acceptable result s) radiotherap 3 (grjp. ; 2) i y departments with poor results (graph 3). The first and second graphs ci early show a tendency towards an improvement of the clinical dosimetry over the period covered and D e attributeintercompnrisob TL thi n e ca sth o t d n helpin e medicath g l physicists to check more carefull e parameterth l al y s involve e measuremeneh n e i d th f o t output of their Co-60 machines. Graph No. 3, on the contrary, shows that the D intcrcompariso'I. I o significann d ha n t influenc e procedureth n o e r measurinfo s g the Co-60 machine outpu n thesi t e seven radiotherapy departments. Onle on y department (Am s subsequentl)ha y produced deviations whic e positivar h d an e t diffeno o d r greatly froe measuremenon m o anothert t A secon. d department

Tl (15);) has two erratic values (one of +h.5 and another of -21.0%) and five correct values A thir. valueo d tw departmen s s ha whic c -20.0) ar hOr t % and -15.0% and one which is correct.

e deviationTh s encountere n somi d e other department ) deviatsKa (Al, La ,e fo a certair n minue perioth n si ddirectio n then suddenly after 1976-77 change to the opposite direction, only to alter again later on with the exception of Al, which remains with quite high positive deviations. This inconsistency of values obtained clearly shows inaccurate clinical dosimetry procedured an s shoul e followeh d n enquira e institute th y b do t y s concerne n ordei d o t r detect the sources of errors. IAEA and WHO should concentrate their attention n thoso e radiotherapy departments with results show Grapn i n . 3 h

Discussio e resultth d f counteo nan s r measure

In order to find an explanation for the deviations encountered a mission by a physicist with a calibrated secondary standard dosimeter was organized early in 1978 to the departments shown in Graph 3, with the exception of one. The finding f thio s s investigation were that:

the clinical dosimeters used by three of the departments were not working properly causing inconsistent data to be obtained;

the remainder of the departments had one or more dosimeters in perfect workin e procedurg th orde t r measuremenbu r fo e e machinth f o te outpus wa t inadequat e correctioth r o e n factors (pressure, temperature) were wrongly applieo lac t f reliabl o ke du d e instrument r sucfo sh measurements and/or inadequate trainin e locath lf o gmedica l physicists

As a result of this investigation a decision was taken to purchase three w clinicane l dosimeter r thosfo s e departments where faulty dosimeters were being used and to organize a refresher course on clinical dosimetry for medical physicists from all departments witli inconsistent results.

The experience presented here shows how the 1AI.A/WHO postal TLD intercompariso usee o identift li d n ca n y places where clinical dosimetrf o s i y a low standard and to determine appropriate counter measures. In order to make further improvements it is suggested that the IAI.A/W110 Network of Secondary Standard Dosimetry Laboratories should be actively involved in the assessment and follow-up of TLD results and in undertaking appropriate action to raise the level of clinical dosimetry.

Another essential factoe considereb o t r s reducini d e ratheth g r lengthy delay betwee D dosimeternTL receipe th f n Vienno ti s d e sendinan th a t ou g resulte variouth o t ss radiotherapy departments throughou e worldth tf thiI . s e achieveb n ca a mord e direct impac n clinicao t l dosimetr e expectedb n ca y .

A final comment concern e sendinth s e d dosimeterreturth an g f o n d an s the need for improvement in this respect. The number of non-returned dosimeters remains high, some being los n mailini t g either r posprioo o tt r irradiatio^ d other.m t beinsno g irradiated becaus f equipmeno e tf ordero bein t ou .g

A gradual improvement in the number of dosimeters being returned has taken plac d bettean e r contact maintained wite variouth h s radiotherapy departments. Letters were sent to all departments to ascertain their willingness to participat a give n i en batc d dosimeteran h s sent onl o thost y e which replied positively. Reminders were sent to all departments which did not return the dosimeters by the fixed deadline and this has caused the number which have not been returned to decrease substantially.

Mailing the dosimeters represents another constraint as postal and custom authorities sometime e x-rayus s o chec t scontene th k f packageo t r o s fear that packages might contain explosives Eastere th n I n. Mediterranean Regio e existencth n f diplomatio e c pouche e participatin th o mos t sf o t g countrie f greao s twa s hel n forwardini p d recoverinan g dosimeterse th g .

28 Table I

TLD Results expressed in Percentage Deviation from the (Uven Dose for 3 Radiotherap2 y Department 2 Easter1 n i s n Mediterranean Countries

f measuremento . TotaNo l No.os ideviatio-wit % a h n Couny tr RT Dept. Measurements +5.o t 0 0+ ' +_5.1 to +J0.( +_10. +20o t 1 . over +20.1 1971-1978

1i N | 5 5 0 0 0

2 Al 6 0 3 2 1 Cu 4 1 (1 3 0 Ccl 6 4 0 2 0 Cm 3 0 1 2 0

3 A 2 2 0 0 0 Is 3 3 0 0 0 Sw 6 4 2 0 0 Tel 5 3 2 0 0 TMH 2 1 0 1 0 1

4 Bg 7 5 1 0 1

5 Ha 4 4 0 0 0

f, Ani 5 0 2 3 0

7 Sll 6 5 1 0 0

8 TU 5 2 1 2 0

9 Ka 7 2 1 3 1 La 6 2 0 4 0 II 4 1 3 0 0 M 2 0 2 0 0 P 4 1 1 2 0

J 10 Ku 4 4 0 0 0

] 1 D 2 2 0 0 0

12 Tu 6 5 1 0 0

TOTAL: 23 104 56 21 24 3

% - 100.0 53.9 20.2 23.0 2.9

29 TLD INTERCOMPARISOIM IN EMRO 1- RADIOTHERAPY DEPT WITH GOOD RESULTS

2 - RADIOTHERAPY DEPT. WITH ACCEPTABLE RESULTS 5

13 _1_J———l————L ' m a 2 H ' n ZI ' SCQ XE7 wn n xx i xx 3 7 2 7 1971 74 75 76 77 78

30 3- RADIOTHERAPY DEPT WITH POOR RESULTS

n m s vm xi ZED SDK 1971 72 73 74 75 76 77 78

31 Next page(s) left blank SURVEA CLINICALLF YO Y APPLIED DOSIMETRY

W. SEELENTAG* Radiation Medicine Unit, World Health Organization, Geneva

1. Introduction

Biological evidenc s beeha e n.V. obtainee Andersoth t a d n Hospital, Houston,

Texas-, accordin c whict g a differenchn arrlie i « -7 e V ctherapeuti f th o dose n i e c ranee already result n increasei s d tumour recurrenc e cas f th underdosago e n i e n i d an e aggravated side effects and darcap.e in the case of overdosage. Unavoidable uncertainties in tur.our localization and definition of the tumour volume in clinical routine work occupy practicallv fully this therapeuti e accuracc e physicath rane th d f an eo v l aspects of clinical dosiir.etrv should therefore be much better than ^7%. The absolute accuracy of the realization of radiation units in Primarv Standard Laboratories, e.e. NBS, NTL, ?TE, is ouoted in calibration certificates for clinical dosimeters to be about *2 to 3%. Experience in the IAEÂ/KHO Network of Secondary Standard Dosimetrv Laboratories (SSDLs) bv intercomparin e calibratioth g a referenc f o n e instrumen 7 laboratorie1 n i t s has, however, demonstrated that the calibration of secondarv standard dosimeters and the transfe e uni f radiatioth c t f ro a "fiel o t n d instrument" aareworldwida n o e e scalo t e ^uch bette f appropriatelri tha " -2 n y performed.

One maior component of WHO's programme for imrovine, promoting and strengthening radiothera^v as an essential part of cancer control is therefore clinical radiation dcsi^etry. Three approaches are used:

) (a prorotic e traininth f d educatioo n an g f redicao n l physicist d theian s r appointment in radiotheranv institutions as partners - not iust auxiliarie e radiotheraristth f o - s ;

(b) establishing in all W.O Regions '/HO Coilaboratinc Centres for Secondarv Standard Dosin-.etrv (SSDLs n orde)i o facilitatt r e useth f o r r fo e radiation e radiotherapth , y institute, acces o calibratint s g facilities where the clinical dosimeters can be calibrated and regularlv recalibrated.

* Present address: Bundesministeriu Innerns mde Bonn3 ,5 , Postfach, Federal Republic of Germany.

1 Shukovsky, L.J.: Dose, time, volume relationships in squamous cell carcinoma of the supragloltic larynx; Am. J. Roentgenol. 108 (1970): 27-29.

33 This is necessarv as individual dosimeters varv in sensitivity and energy response, etc., and their characteristics mav even change with time. Accurate calibration of a dosimeter is, therefore, the first prereauisite fon accurata r e measuremen f doseo t . Furthermore n SSDa , L should builp u d regional and local expertise in the field of dosimetrv, act as regional or national advisor to the user (radiotherapy institutes, but also radiation protection services and e.g. industrial users of radiation), and undertake educationa d traininan l g activitie n radiatioi s n physic d dosimetrvan s . e targeTh f thio t s programm e availabilitth s i e t leasa e appropf on to v - riately qualified SSD eacn i L h maior f radiatiocountro e us whicn i ve nth h and radionuclide t iusno ts i snegligibl d easan e v accesa n SSDa n o i Lt s neighbouring countrv for the user of radiation in a country without its n nationaow l SSDL o meeT . t that target n closi , e collaboration witd an h e initiativth e Internationan o th f o e l Atomic Energy Agency e join,th t IAEA/WHO Networ f SSDLo k s establisheswa n 197i d d includepan t Septembe(a d r 1978) already 39 regular members, and 11 affiliated members (Rational Primary Standard Institutes, e.g. the National Bureau of Standards, NBS, Washington).

(i) the validity of calibration of the clinical dosimeters used;

(ii) the accuracy of the irradiation equipment including its shutter mechanis d timinan m g procedure;

e abilite institute'th (iiith f )o y s staf o accuratelt f y set-up patients (checke v measurementb d n simplo s e phantoms);

(iv) the professional capacity of staff to reliably irske the dose calculations necessar r applyinfo v g radiotherap - sucy h surveys furthermore allow:

) (v e individuaadvice giveth b o o t t ne l institut n casi ef pooo e r results on how to improve the quality of work and avoid mistakes;

(vi) decide whether sendin a consultang e institutth o t t o chect e k locall e procedureth y s applie d providan d e local trainins i g necessarv to improve the situation", or,

(vii) conclude that due to the frequency oc events in ?. eeoeraphical region it is desirable to establish local or regional training activities in order to improve generally the level of professional competenc e relevanth n i e t countr r reeiono y .

e long-terth n I n plannin s expectei t i g d that finally each national SSDL, M IfflO Collaborating Centre or ember of the IAEA/WHO Network of SSDLs, performs such intercomparisons and surveys independently of each other in their geographical are f competenceo a . International coordinatiov b n e Networth r s suco a k O h WH wil IAEd lan A the e limiteb n o harmonisint d q the methodology applied by the various SSDLs to »-aV e their results internationally comparabl o chect d k an e'-hethe r svsteratic deviations occur.

Some SSDLs have already starte o implement d t thei n programmeow r r fo s "postal dose intercomparisons e participatinar d an " n internationaa n i g l e IAEAprogramme r th comparin fo ,y b n ru ,g such programes e majoritTh . y of countrie n thii s s world are, however t covereve t y sucno b ,d h national or regional programmes and this is the reason th,at IAEA and WHO still continue the "IAEA/WHO Postal Dose Intercomparison Programme". An evaluatio s resultit e f presenteo nar s n thii d s paper.

2. The IAEA/WHO Postal Dose Intercomparison Programme

Apart from sendin n expera g n dosimetritow wit s hhi c equipmen radiotherapa o t t y institution (RTI) for checking all procedures applied, there is only one possibility for intercomparin d surveyinan g g clinical dosimetrv: thi s sendini s y mai (b r gthrougo l h other channels of communication) a dosimeter to the RTI, with the request that it be irradiated under prescribed conditions wit prescribea h d absorbed dose d measurinan , e th g

34 absorbed dose received by the dosimeter after it has been returned. Unfortunately, the classical dosimetric metho measurinf o d numbee th g f ionizationro s produce y radiatiob d n in a defined volume, is not appropriate for that purpose. Other effects of radiation on matter need to be used. Considering the existing possibilities therefore IAEA in 1969 decided to investigate the use of the "Thermo-luminescent-dosircetry (TLD)" -principle for "postal dose intercomparisons". Detail f thio s s principl describee ar e mann i d y publication d therefor an st repeate no e ar ed here.

n 197I O joine0WH de implementatio th fAE n i A e IAEA/WHprojece th th d f o nan t O Postal Dose Intercomparison Programme started n thiI .s programme IAEs responsiblAwa e r preparin fo D set TL dosimeterf o se th g measurind an s radiatioe th g n dose receivey b d the sets returned, WHO took care of the distribution and recollection of the dosimeters throughou worlde th td acte,an d together wit evaluatiohe th IAE n Ao f resultso n d ,an initiating corrective measures where necessary.

followine th n I resulte IAEA/WHe th gth f so O Postal Dose Intercomparison Programme are described and critically evaluated.

1 Methodolog2. y

Lithiuro-fluoride powde plastin i r c capsule representins- thermoluminescena g t dosimeter (TLD sens i participatino t )- g institutions e instituteTh . e ar s requeste irradiato t d e these capsules under prescribed conditions wit prescribea h d radiation dos d returean n them throug O channelWH h IAEAo t s , wher radiatioe th e n dose receive e capsuleth y b dmeasureds i s e "setOn . f dosimeter"o s consistf o s 6-10 cansule differenf o s t kinds intende evaluato t d dosee th e , doserate, additional dose received r "fading,o " during transport d consistenc,an resultsf o y e Th . institutes also "data fil n i la sheet" whicn ,i h they describ w theeho y calculated and arrived at the dose given to the capsules. The difference between the measured d quotean d dose give n percenquotei e n th f do t indicate e accuracth s f dosiroetro v y e relevanth n i t institute, whereb negativa y e deviation means thadose th te really administered was smaller than intended (quoted) and vice versa. Accordingly, completed "data sheets" frequently enable the source of errors to be located. In other cases comprehensive correspondence, repetitio measuremente th f o n r eve,o n sendin expern a g dosimetryn ti , solve problee th s d improvean m e accuracth s f o y radiotherap e relevanth n i y t institute.

2.2 Results 1969-1978

Documenn I D 40/7tRA evaluatio n 6a resultf no untip u s l 197 s provided6wa . The present evaluation, covering the period from 1969 to 1978 is, however, not just an extension from 1976 to 1978, but a revaluation of all data available by. September threo 1978t 0 set 8 o dosimeterf eo so .Tw t batche 0 4 f o ss were distributed and recollected annually. Details of the batches and their distribution to O regionWH x e showsi ar s A Tabln totae i n th f . 101o 1 le 1 set f dosimetero s s have been distribute f theo d r% ove recollecte85 year0 1 rd an s d evaluatedan d needt I . s to be mentioned that onlv a few of the unreturned, unirradiated or unevaluable dosimeters (all included in the tables as "not returned") were "dropouts" due to condition f controusere o th t ,f ou slo e.g . failur mailinf o e g services, etc. Unfortunatel majorite th y y reflect e carelessnesth s participatine th f o s g institute d lac an f intereso k improvinn i t n workow qualite s . th git Considerinf o y g that material costs and the work of international staff involved amount to approximately US$ 50 per set of dosimeters, the waste of 15% of the dosimeters distributed is a wast f aroun0008 eo $ ,US d leadin o considerationt g whethef o sjustifiabls i t i r e to perform such intercomparisons free of charge for the participating institutions, particularly as they represent direct assistance to countries rather than an investigatio purpose th r f IAEWHOeo nd fo an A . Chargin r participatiofo g e th n i n programme would, however, havadverse th e e effect that manI interesteRT v n i d improving their quality of dosimetrv are prevented from participating for administrative and budgetary reasons.

A similar observation was also made by WHO in distributing free of charge personnel monitoring dosimeters (film badges), which were fullv financed bv extra- budgetary contributions (provision to WHO free of charge bv the Service Central de Protection contre les Rayonnements ionisants under Professor P. Pellerin and the Personnel Monitoring ServicGesellschafe th f eo Strahlenschutzr tfü , Neuherberg, under Professor Wachsmann). Here again reture ,th n rat mucs i e h lower than when participant e chargedar s e misusTh .wastd an ef service o e s provided fre f chargo e e is a serious problem which needs further consideration.

35 In Table 2 data for 1969 to 1978 are split into VHO Regions, Africa has not vet participated e programmth n i e (aoart froir pilot studie whicn i s n 196i h 9 South Africa and Southern Rhodesia were involved). RT has developed on this continent durin e lasw yearth gfe t s onlt thibu y s momentum will increas futuree th l n Al i e. othe O regionWH r s particinated nearlv eouallv with aroune th 5 eac f 1/ do h distributed dosimeter sets. Seventy countries, representing more thae n th hal f o f O MembeWH r States participated d altoeethean , I throughouPT 6 41 rworle th t d were checkedf theo n% participate50 . d once onlv 7 mor10 ; e tha 5 timesn e relativelTh . v high rat f 32-33o e f institute%o s participating nore tha Eastere 5 timenth n i sn Mediterranean (EM d South-Eas)an t Asia (SEA) demonstrate specifie th s c interesf o t some RTId Darticularlan s e Regionath f o v O Regional WH Adviser e th ln i Offices o t s e situatiogeth t n under control. Considerable differences exist between regionn i s the percentage of "not returned etc." sets. This rate of "waste" is below 102 for e South-Easth r fo % e Europeat 21 th Asi d Westerd an aan n8 1 s higRegion a s a hd an n Pacific Regions respectively.

n e Tabl"noI th t3 e returned etc." set f dosimetero s e listear s n relatioi d o t n the frequenc e programmeth f participatioo n s vinterestini i t I I RT . n a o t gf o n note that 38% of all institutes which participated once or several times did not retur e dosimeterth n t leasa s t l instituteoncd 7.5al an t e retur f no %o d ndi s them two or more tines. It is unfortunately obvious that such failures are not normally e mailin e faulth th f o tg svste ? countr n i md failur an v o returt e dosimetea n r should thereford unreliablan d ha e judge eb a es a resultd .

e followingth n I , however, onlv result f returneo s d measurablan d e setf o s dosimeters are analvsed. Table 4 provides the summary of data split according to WHO "eeions and into periods of time, I including batches I to XI, and II including batcheo XXIIt I I XI srespectively e periodTh . s coveyeare th r« 1969-197 d 19743an - 1978 resuectivelv r botfo h m periodsu e s alsTh i s. o nuote worle th wels a dds a l total. Finallv, the results in a number of sinele countries are given wherebv the relevant O RegioVP s mentione i ne country' th t bu d s name codified. "Results e interth f -o " comparison are expressed as % deviation of the dose measured from the TLfi by IAEA (M..) and the dose auoted bv the relevant RTI as havine been administered (0) to

the M cansules according to the formula.

M M -O Deviatio ——-—0 = ' 10 n x —

e evaluatioth r Fo 7 classen f deviationo s e definedar s :

% = +10. 20 D o t 1 +5.= % 10 C 1o t = % +2.5 = +27.B A o 1t

E = +2O.1 to 50% F = +50.1 to 100% and G = above +100%

In Table cumulativth 4 e e percentag numbee th f resultf relevane o ro e th n i s t clas e auotedar s . e tota100th %ls i numbe f dosimeteo r r sets returne d evaluatean d d for the relevant line. The third column therefore gives the percentage of results within +2%, the fifth column those within +107- (= the sum of class A + E + C) . The sixth column includes the sur of D and all higher classes; in other words, all result e qualitTh s abov f result. e variouo y on th e o n s +10i s s d classe%an e b n ca s defined as: A = excellent and a deviation of this size is not significant as it is within the maximum achievable accuracv of the TLD nethod under the given conditions. B = good and some values in this class near to 2% rav even result from exceptionally greater rando D methodmTL e error f neareth 7 thei ;5 f o syo t rshould , however, lead to a check being made of the irradiation and calculation procedures and the deletion f smalo l errors, when detected .t eoono Clas d= althougo C serious to d t an sno h should lead to a careful checV being made of all procedures applied, including perhap a srecalibratio e dosimeteth f o n f thii r s e samresulth e n i directiot n (either olus or rinus) is repeatedly obtained. The error in class D is totally unacceptable for effective radiotherapy and immediate steps need to be taken to locate and correct the error and improve the quality and accuracv of work. Class E and higher mean a total disaster if patients are treated vitb that accuracv. Serious conseouences will result and immediate expert advice from outside the RTI, perhaps fro nearba m y SSDL, shoul e requesteb d o locallt d y chec proceduree th k s applie d givan de on-the-spot training.

36 In the last columns the nutr.beT of countries included in the relevant line, the numbe f participatino r nun-bee gth PTlf dosineted o r an s r sets distributed e givenar , . The final colunn gives the dosimeter sets vhich have not been returned, not irradiated r cannoo e evaluateb t r varioufo d e numbeth s f f setreasono o r % s n distributedi s .

Although the table is self-exnlanptory a few noints mieht, however, be extracted: the results vary considerablv between the various regions. Africa (AF) should not be considered in this context as only a few selected RTI participated in the first pilot batches, in order to check the suitabilitv of the intercomparison method. Good results withi T deviatio+5 n n ovewhole th r e period 1969-1978 were observe a littl r fo de ove% 5^ r neasurerente oth f Latin i s n America (Latin-AM), Eastern Mediterranean (EMd )an South-East Asia (SEA), whereas Europe (EV Westerd )an n Pacific (VT) regions show more than 60 to 703 good results, compared with 59% for the world total. 28 and 29% of the results were not acceptable at all (more than +10% deviation) in Latin-AM and EM e worlrespectively e resultth th dr f fo o totals . % 27 20 . ,d comparean D E r dfo wit% 10 h for Latin-AM were out bv more than +50% during the first period and 0.5% for the world total in both periods.

A review of the data split according to single batches was made to check whether the situatio d irproveha n d vear0 durin 1 programme e th s th e s beeeha n runningt . no Thi s swa demonstrate e proportioth s a d f eaco n h batc e differenh th sen o t t regions varied considerabl programme th d an y e increasingly concentrate n regiono d d countriean s s mosn i t need of advice. Comparing the two periods 1969-1973 and 197^-1978, however clearly demonstrate n improvemena s n Latin-AMi t , wher numbee th e f totallo r v unacceptable results was reduced from 42 to 21% and the good results increased from 36 to 59%. Sir.ilarlv, the situation has improved in SEA. In EM the results in the second period worsened because the programme concentrate n thoso d e countrie d PTIan ss mos neen i tf improvement o d . This region also demonstrates the need for locally given expert advice.

e valueTh variour fo s s countries demonstrat e eveth en ereater differences between countries figuree th ; swhole refeth eo t rperio d 1969-1978. r examplCountrfo ) e(g v show H goo 88 swer% d 12 rese resulte f th o "dropouts"(>10t d an s % deviation),(total no.of sets distribute however, is d , verv small). Another countrsame th e s nearl f resioo vha ) y(h n one-half dropout d onlan sy one-quarter good results e highlOn . y industrialised country 5 goo/ 4 d s result ha % dropouts U o15 t stilE f bu s ha l .

An evaluation is given in the last three lines of Table 4 of the results of intercomparisons obtained with the repeated participation of institutes which once or several tires did not return the TLD (N average). In line "N before V" the results of the participation precedinn.r= s availableN a " . r e etc.fa th g s ")(a were evaluatede Th . distribution of values within the various classes belongs to the lower qualitv distribution, those "after H" are a bit better, those "before N" a bit worse. Final conclusions cannot, however, be drawn from these observations.

These examples demonstrate that o regiothern s d practicalli ean n o countre n v th n i v world which does not need to make continuous efforts to get accurate clinical dosimetry appliel radiotherapal n i d y institutions e maioritth ,n i evef institution o f y i n e th s standar s highi d .

e occasionallOn y hear e argumenth s t tha a deviatiot n dosi n e froie internationath r l standard does not matter as lone as it is consistent within the institute; in other words e samth e deviatio n ii th directio fe samd th an es i n n (plu r minuso s ) ovee vearsth r , thee institutth n e woul dn empiricall ow appl s it y y found therapeutic dose. This argument is not considered valid in the opinion of most experts. Nevertheless, it was thought to be of interest to check the consistency of results of institutes participating more than once in the intercomnarisons. The data are presented in Table 5. 205 RTIs or 49% of the total 416 participated more than once; of these, 66 twice, 45 three times and 94 four and more times. The table shows the percentage of the institutes in the relevant column belongin fivo t g e classe f consistencso y rangin gmoro t fro e% 5 mtha n 40%e Th . relevant class means thahighese th t t measured deviation differs froe lowesth m t measured by the percentage indicated by the class. Class A, for example includes differences from 0% (e.g. +A +A for the "highest" and "lowest" deviations, or +B +B, or -C -C etc.) up to 5% (e.g. +A -A, or +B +0, or -C -B etc). Class B includes e.g. +A -B, or +B -B, or +C +0 etc. and so on. The values quoted in brackets (...) indicate the percentage of institute e relevanth n i s t colum whicr difference nfo th h highesf o e d lowesan t t deviation does not include the +5% class of deviation from IAEA measurement and all deviations are either in the plus or minus direction. In column "twice" for example 35% of the 66 institutes in class A, which could e.g. be +A -A or -B -C etc. (18)% outside the +5% class therefore are +C +B or -B -C pairs, 35-18 « 17% are +A -A, or +B +0 and similar.

37 Considerin 5 institute20 l al g s togethe remarkabls i t i r e tha f theto e onlar m% 19 y consistent in their dosimetry within 5% and only 13% of them (19-6) are also in agreement wite internationath h l standard f theo % m) demonstratE 55 (clas .o t C s e differences in their applied dose of more than 10%. The statistics of consistency are much better for those which participated twice or three times onlv. This is easiIv explainable for two e increasereasonsTh ) (1 :d number participatiof o s n increas e chancth e f detectino e g errors occurring randomly rather than systematically ) Institute(2 . s wit d resulthba s were usuallv requeste participato t d e nexe agaith t n i nbatch n iudginI . e resultth g s one should not forget in addition that the higher classes C to E also include those institutes which first showe d resultba d d thean s n improved. This evaluation anyhow demonstrate e invaliditth s e argumenth f o v t that consistenc f dosimetro y n indiva n i y - idual institut mors i e e important than accurac n relatioi y o standardt n . Institutes which were consistent (clas , perhapA s s als wer) B o e usually also goo n relatioi d o t n the standard; those deviating from the standard were almosr all also bad as regards consistency.

. 3 Conclusions

3.1 The situation regarding the accuracy of clinical dosimetry still requires considerable effort practicalln i s O "egionn almosi WH l l countried al al tyan s o t s ensure that the existing radiotherapy services, particularly in developing countries, but also in industrialised ones, deliver accurate tumour therapy which is essential e effectiveb o t s e IAEA/WHi Th t .ii f O Networ f Secondaro k y Standard Dosimetry Laboratories (SSDLs) should obtain increased suppor d strengtheninan t y nationab g l and international authorities in order to enable it to become fully operational and effective in the shortest possible time, and particularly to fulfil its advisory and educational function worldwida n o s e basis.

3.2 It is considered desirable that it be included in codes of practice or even made compulsor y nationab y l authoritie y radiotherapan r fo s y institute involven i d cancer therapv with high energy radiation to regularly - say once a year if the result e goodar s ; more freauentl t acceptablno f i v e deviation e observear s - d participat postaa n i e l dose intercomparison simila o that r t oreanize y IAEA/WHOb d . e SSDLTh s shoul e stimulateb d d supportean d n organizini d g such nationa r regionao l l intercomparisons e timth e r beinFo . g alse IAEA/WHth o O Service e user b fo n d ca s that purpose. Services offere y SSDLb d s should n additionaa s a , l safety measuree ,b regularly intercompared on the international level, and this could perhaps be organized by the Network.

3.3 Services of short-term consultants should be made available at relatively short notice to RT institutions which cannot manage to solve their problems by themselves. Experts from WHO Collaborating Centres and SSCLs should increasingly be appointed for such missions.

3.4 The training of radiotherapy staff, including physicists, radiotherapists and medical radiological technicians n clinicalli , y applied dosimetrv shoul e strengthb d - ened and short, practically oriented training courses organized on a national or regional basis, whereve n increasea r d frequenc d resultba f o s yobservei s a n i d country or region.

3.5 The above recommendations do not conflict with, but rather complement, WHO's prioritie e fiel th f Primar o dn i s y Health woult i Care e ethicalls b da , y unacceptabl o establist e h Primary Health vhos f o Care e e e?rl ,on th aim s yi s detectio f cancero n , without establishin r bringino g g existing hrslth servicer fo s cancer treatment to a stage of development and competence where thev can effectively treat cancer patients. Reference is made in this context to the report of a WHO Meeting of Investigators on the Optimization of Radiotherapy particularly in developing countries held in Cambridge, UK from 11-15 September 1978. It is expected that this report wil e publisheb l d during 1979.

38 Table 1 - Distribution of TLD 1969-1978

Nunber of Sets to Pegion Batch No. Date AF AM EM EU SEA KP TOT. n.r . etc

Julv 1969 ) Partiallv (Not all results available II" October 1969 ) included as trial donv b e IAEA III0 December 1969) in I-III alone) . I April 1970 5 2 6 36 5 6 60 18% II August 1970 15 9 18 22 4 68 10% III December 1970 3 38 1 12 12 8 74 12% IV April 1971 3 12 21 6 - 42 12% V July 1971 6 2 9 8 14 39 8% VI November 1971 1 - 1 1 37 40 40% VII March 1972 - 2 35 - - 37 8% VIII July 1972 5 20 9 7 - 41 27% IX January 1973 - 3 17 - 22 42 14% X May 1973 - - 14 10 10 34 6% XI October 1973 11 8 7 7 5 38 21% XII January 1974 20 2 - 1 18 41 20% XIII May 1974 11 - - 1 11 23 0% XIV October 1974 16 12 3 5 - 36 39% XV April 1975 19 - 8 - 12 39 10% XVI August 1975 15 - 1 - 21 37 16% XVII March 1976 S 18 - - 18 44 11% XVIII August 1976 1 15 8 24 - 48 31% XIX December 1976 10 - 1 21 - 32 9% XX May 1977 17 16 - 34 10 77 9% XXI November 1977 9 15 - 35 ]0 69 6% XXII July 1978 - 15 4 28 3 50 6% XXIII September 1978 (Not vet available, November 1978)

TOTAL 8 207 156 204 227 209 1011 15%

* = not returned, or not irradiated, or not évaluable due to pistakes in handling e Instituteth y b D thTL .e

39 Table 2 - Other Data split by Regions

Ar AM TOTAL

Sets distributed 0.8%20.5? 15.4% 20.2% 22.5% 20.7% 100% Sets n.r. etc. 0? 137. 1C?. 9Ü % 15 182 % 21 f Countrieo . No 2 s part. 20 13 17 7 11 70 No. of Institutes part. 7 121 38 115 60 75 416 Inst. part. 1 tine 86% 667 24% 57" 4fi"277 50% 2 tir-es 1Ü? 137 13Z 22;; 122 237 17% 3 tines 9% 8% 15% ? 12 T7. % 23 4 tirpes 7 2 r 8i ' n i 157. 77 5 times 27, 13" 2r 32 87. 47 + Line 5 s 27, 32Z 1% 33" j% 107.

Table 3 - Kot returnen ( d .r. etc.) Sets Snlit according to frequency f participatioo n

Participation (times) 1 234 * 5 TOTAL We. of Inst. n.r. once 30 20 11 5 21 87 = 14% - 14% =7.5%% =21 4- % % 23 = No. of Inst. n.r. twice - 4 5 9 7 25 % 7 = % 3 •=- 3' =2% =6% No. of Inst. n.r. three - 0 0 8 S and store times = 247 = 2%

40 Tnblc It - Results of TLD Interconn.iri sons

WHO CLASS A A + B A+B+CG o t D E to G F + G No. of No. of No. of Of these PERIOD REGION -2% ±5% ±10% •> ±10% "> ±20% > *50% Countries Inst. sets distr. n.r. etc

AF* I 25% 63% 100% - - 2 7 8 0%

I AT I N I 14% 36% 587 42% 13% 2% 56 81 21% AM IT 31% 59% 79% 21% 8% 1% 91 126 9% 1 + II 25% 51% 727, 28% 9% 1% 20 121 207 14%

EM I 24% 60% 76% 24% 2% 29 63 21% II 27% 48% 67% 33% 4% 30 95 13% 1 + II 26% 53% 71% 29% 3% 13 38 158 167,

EU I 31% 73% 90% 10% 3% 112 179 8% 11 25% 50% 85% 15% - 15 24 17% I I + I 30% 70% 89% 10% 3% 5 11 17 203 9%

SEA I 30% 52% 70% 30% 7% 36 78 22% II 24% 58% 87% 13% 4% 0.8% 49 148 16% I + 11 26% 56% 82% 18% 5% 0.5%7 60 226 18%

VP I 34% 55% 82% 18% 12% ]% 64 103 25% II 35% 72% 86% 14% 7% 57 110 16% I + II 34% 64% 84% 16% 9% 0.6%11 75 213 21%

WORLD I 28% 59% 79% 21% 6% 0.5% 304 512 17% TOTAL II 29% 59% 81% 19% 5% 0.5% 242 503 14% I I + I 28% 59% 80% 20% 6% 0.5%70 416 1015 15% Tabl Continue- 4 e d

WHO CLASS A B + A A4B+CG o G t + 0 F G o t E No. of No. of No. of Of these PERIOD REGION ±2% ±5% ±10% :>±20% >±50% Countries Inst. sets distr. n.r. etc COUNTRY LATIN (a) 31% 6% 1 29 37 14% AM 19% 50% 69% (b) 33% 65% 79% 21% 9% 1 28 47 9% (c) 30% 50% 77% 23% 10% 3% 1 27 36 17% W) 30% 50% 60% 40% 10% 1 7 12 17% (e) 13% 38% 75% 25% - 1 8 10 20%

EM (f) 32% 68% 86% 14% 7% 1 11 35 20% (g) 38% 88% 88% 12% - 1 5 10 20% (h) 14% 24% 55% 45% 3% 1 5 31 6%

EU (i) 25% 58% 88% 13% 8% 1 10 25 4% (k) 31% 71% 94% 6% 3% 1 24 39 10% (1) 31% 77% 85% 15% - 1 26 28 7% (m) 20% 53% 80% 20% 7% 1 8 19 21% (n)" 56% 89% 100% - - 1 9 9 - (o)* 50% 67% 100% - - 1 6 6 -

SEA (P) 22% 53% 80% 20% 5% 1 44 144 17% (q) 36% 64% 82% 18% - 1 5 15 27% (0 (r) 34% 72% 86% 14% 7% 3% 1 5 32 9%

WP (s) 46% 82% 100% - _ 1 11 32 13% (t) 37% 60% 79% 21% 10% 1% 1 36 99 31% (u) 29% 57% 95% 5% 5% 1 7 25 16% (v) 27% 58% 69% 31% 15% 1 11 30 13%

N average 25% 51% 73% 27% 7% 1% 416 38% N before N 19% 45% 69% 31% 7% 58 N after N 26% 52% 76% 24% 5% 58

Nota: Period I = 196o 197t I 9X 3 o Batct inclusiv I h e Period II o XXIIt Patc I = I197 XI ho 197 t 4 8 inclusive

N average Resultl setal s f distributeo s o institutet d s which have onc r moro e e time t returneno s a setd , H before N Result f seto s s obtaine t returnedno s d wa befort . se a e N after N Results of sets obtained after a set was not returned. *• Only selected institute r thafo s t countrv(ies) participate e firs lotth i (n n t)i d batche n ordei s o chect r k the suitability of the intercomparison method. Tabl Result- 5 e f Repeateo s d Measurements

4 and Total ir>ore Participation: 2 times 3 tines more tipes than once No. of Institutes 66 = 100% 45 = 100% 94 = 100% 205 = 100%

Class t returnese o N d 6% - - 2%

A 0-5 Z 35(18)% 27 (2)% 4 (2)% 19 (6)% B 6-10% 29 (9)% 36 (4)% 17 (3)% 25 (S)% C 11-2"% 24 (9)7 20(11)7- 26(10)% 24(10)% D 21-40% 2 (2)% 7 (4)2 28 (9)7. 15 (5)% E >40% 5 (3)% 11 (7)% 26(13)% 16 (8)% All i(% Total) 32% 22% 462 100%

Values in (..) = % of values outside - 5% in absolute terns (i.e. all values of the institute either oositiv r negativo e e deviations).

43 Next page(s) left blank DOSE INTERCOMPARISON PROGRAMME OF THE REGIONAL REFERENCE CENTR ARGENTINF EO A

R. GONZALEZ SARAV. M , FERNÂNDEE ÏD Z GIANOTTI Direction de Raclioisötopos y Radiacioncs, Comisiôn Nacional de Energfa Atômica, Buenos Aires, Argentina

AbGtract

DOSE INTERCOM?A.R RAMMC RO TÎIF E0 P E N IREGIONASO L REFERENCE CITCTE ARGENTINAF O R .

This report include briesa f activitiee surveth f yo s developed in the Regional Heference Center and a description of the TLD teletherapy interconpar-ison programme baaed on the original IAEA/WHO studies. Results oabsorben fa d dose intercompariso 8 therap1 f o n y unit e presentedsar .

1. TNTKOX'CTIOM

The Regional Reference Cente Argentinf o r s establisheawa y b d agreement betwee Worle th n d Health Organizatio Conisioe th d nan n Nacional e Sncr/jld a Atörnic f Argentino a cooperation i a n v:itInternationae th h l Atomic lancriry Agency, in 1968. This Regional Reference Center is a Secondary Standard Dosimctry Laboratory that belongIAEA/WHe th o st O network similas A . r laboratories existing in other countries, it was established due to the necessity of improving the treatment planning in radiotherapy services and increasing the participation of the physicists experienced -_n this speciality and was the natural step in the developing programmes in radiotherapy physics establishe t thada t tim Argentinan i e . The; principal aims or these laaoratorLejo arc: to calibrate radi'ition measurement instruments used for radiotherapy ana radiation protection; to -?ivc advice on radie Lion doaimctry in oLinical work; and to develop a training progranoe in radiotherapy physics. >7 n agreemenia 19 n I t with '„he TA.EA viaa si-p-.e n ordei u o develot r p a oonlal dose Lntercomparison programme. It will be explained in detail below.

. " SîJJTPK-WT, INSTRUMENTS AîJD PHINCIPAL TAoKO PERWRMED e availablTh e irradiation source t thisa s laboratory are: v.%'O X-ray .^ennratorc (a 10 - 100 kV Seif art, with a Philips tube and a 80 - 300 kV Siemens Stabilipan), a tcleooba.lt unit (picker and s.mlJcr Co-00 and Cs-137 sources for hor.lth physics calibration. The principal, instruments employed are a secondary standard dosimeter Xustncr-PychlpM o PT^-tw ,J type IXJO a free-ai, r w chambeenergielo r fo rs (n.ado in Argentina), and all the accessories needed to perform the calibration of dosimeters used in radiotherapy and radiation protection.

For thermoluminescent dosimctry TLJ-70F Li , 0 powde uses i rs da detector .TeledynA e Isotopes model 3730C reade uses ri evaluato t d e the detectors. The ri'Lu absorbed-dose values are derived from PTW ionisation chambers.

45 This Center has also a laboratory for chemical dosimetry. The most important tasks developearew no :o t p du (a) Dosimeter calibration. Since 1971» 430 calibrations of radiotherapy instrument 0 calibration14 d san radiatiof so n protection instruments were performed. (b) Training programme. Since 1964» 19 Dosimetry in Radiotherapy courses have been given physician2 .25 physicist8 1 d san s advisers attended these courses d som ,an thef o e m tooka special trainin radiotherapn gi y physics. (c) Radiation dosimetry advisory work has been performed in several radiotherapy services. Cooperatio) (d ninterconiparisoe wit PAHth e n th hOi n quality- control studie r filsfo m badge dosimetry services, madn ei 1975 and 1977. (e) TLD intercomparison programme. This will be explained in nexe detaith t n sectioni l . Developmen) (f ferroue th f o ts sulphate syste higr fo mh dose measurements. This laboratory has participated in the two IAEA high dose intercomparisons mad 197n ei d 1978 7an .

3. THE TLD INTERCOMPARISON PROGRAMME 1 Cooperatio3. n witIAEA/WHe th h O Co-60 therapy units intercomparison programme. Since 197 Argentine'e 4th s SSDcontributes Lha IAEA/Me th o t d O Co-60 Teletherapy Dosimetry Servic sendiny eb dosimeterF gLi therape th o st y center r countrou f so y arid giving them technieàl assistance th n ei experimental procedure for the intercomparison. 197o t participante 5p th U s receive o set capsulef tw dso s containing exposee b specifiea o t o t dLis Fwa powdert d se dos e e.On (200 rad). The other set was to be exposed for a specified time (2 min). The results capsulee th f o s irradiate fixea r dfo d time were considered less reliable than those of fixed dose irradiation (Ref. l). Thus, since 1976 the fixed-dose procedur adopteds ewa . Participants complete data d a sheet and provided information on the basic beam output calibration measurements, the geometry of irradiation and the values of various physical factors that they use estimato dt dose deptm eth ec watern 5 rathi t ea . Table 1 shows the results obtained by the IAEA/WHO for 21 radiotherapy center Argentinf so e durin yeare gth s 197 1977o 4t ' Fro1 2 m intercomparisons (code 619 and 940 are the same center), about 50^ have good dosimetry with a deviation less than HH 5$. Only three centers have a deviation between £ 10$+ _d e onlyf.oan Th y center wit deviatioha n greater tha niOfo+ (code 619 s improve)ha dosimetrs deviatioe it d th t ybu s i n still greater than + 5$« In 1977 °ur SSDL started with a thermoluminescent dosimetry programme, in order to develop an intercomparison programme for Co—60 therapy units regioe ith n n wit same th he procedur employes i s ea IAEA/WHOy b d .

3.2 Activities at our SSDL

Detail firse th tf so measurement r SSDou L t swera e reporteo t d the IAE Januarn i A y 1978 (Ref. .2) 197n I cooperatioe 7th thref no e radiotherapy center Buenof so s Aire obtaines swa orden i d undertako t r epiloa t intercomparison. These center adequatd sha e instrument d highlsan y trained hospital physicists. They were selected to assure a good irradiation procedure. Each center receive capsule6 d s wit powdeP hLi r frosame th me batch irradiatee b thef o otherse o t :m3 th d ,dan without previous irradiation, were kept as control. The centers made the irradiation on the same day, and in order to avoid any fading correction the capsules for calibration were also irradiated in our SSDL on the same day. Once the material was returned to our laboratory all the measurements were performed on the same day. The absorbed-dose values assigned by our SSDL to each capsule and the values quoted by each eenter are compared in Table 2.

46 TABL . E1 Rl-SULT F 'ISO I 113 lAHA/MÜ INTl-RCOMPARISON R ARCLNTINIIO - RADIOTHERAPY ü'NTl-RS SINCE 1974

Yc>,;r- Batch Code MEAN Dosn Deviation DOSE RATE Deviation number calculated quoted1 by (%) moas'.irud quotey b d (%) y b fAF.A participant by IAÏ:A participant (rcid) (rad) ) in r i, (« (r (rad/min)

1974 12 578 487,9 500,0 -2,4 89,4 91,0 -1,8 019 179,5 200,0 -10,2 27,9 29,9 -6,5 620 204,0 200,0 *2,0 65,7 64,0 +2,6 1974 13 621 196,0 200,0 -2,0 58,5 58,6 -0,3 622 200,4 200,0 +0,2 84,8 85,7 -1,0 (>23 200,9 2CO,0 +0,5 83,3 82,3 -1,1 652 184,5 * A 57,2 * * 053 192,6 200,0 -3,7 125,1 130,1 -3,8 1975 14 654 P P P P P P 655 P P P P P P _i 703 165,8* N A 22,5 N * 1975 15 704 204,9 200,0 +2,4 27,6 26,1 +5,5 706 212,0 200,0 +6,0 20,2 19,5 +3,7 1976 17 818 194,8 200,0 -2,6 199,6 +4,7 I977 19 908 209,0 909 204,6 199,5 +2,6 9-10 185,0 200,0 -7,5 941 197,2 200,0 -1,4 042 * P P 1977 20 <>13 191,9 200,0 -4,1 944 P P P 945 182,0 200,0 -9,0 NotedatO N o:* avail.iblc N Data shee t roluvno'A no tAL I o t l P Other reasons

TABLE 2. RESULTS OF SSDL PILOT INTLKCOM'ARI SON

Center Measured, Diff. Mean A Deviation Kean * (V, Craci ) Crad) C%)

I 100,13 (Co -60) 100 ,.13 0,40 199,55 199,57 -0,01 99,73 I 99,16 CCs-137) 100,83 1,67 203,43 200,05 + 1,70 100,00 II 99,94 (Co-60) 100,38 0,70 197,08 200,15 -1,53 ' 99,68 III 101,12 (Co-60) 98,65 2,47 133,48 142,83 -6,55 100,22

Note: Measured,, .....,, , , , —————\ : individual dose values measured for e-icr. capsule expressed ?.eare th .f o dos % e s l threa valu_ al f eo e capsules (reading r sSSDL) ou mad y .b e Diff. %: differenc e between r.;ax fro«ann mi dn three capsules readings s expressea previoun i d s three columns. Mean: mean dose in rad assigned by cur SSDL. quotes a d eac y b d: ra Ados hn i eparticipatin g center. Deviatiocenr pe t deviatio: n% measuref o n d near cosf ,o e (MM) from the quote regarn di dos ) quoteo t d(A e d dose: Dev.% = 100 . (MM - A) A 47 The percentage deviation of three teletherapy units is less than centee deviatioa On s . rha 2% £ n greater tha n'j%.- Nevertheless this center irradiated with a dose lower than the 200 rad required, and beyon calibratior limite ou dth f o s n straight-line. Thus randoe ,th m uncertainty of the absorbed-dose value assigned by our SSDL is greater thauncertainte th n y expecte y thib d spercentage methoth d dan e deviation obtained has less reliability. The first national intercomparison was undertaken in 1978 with 12 participating institutions. 14 therapy heads were checked. Each center received four capsules wite sampowdeP th hLi e f batcho r , thre f theo e m to be irradiated and the other without previous irradiation was kept as control. s requesteItwa dosd deliveree ra "b ecap de 0 -th tha 20 o t da sules at 3 cm depth in a water phantom. The centers received a very simple questionnaire in order to obtain information about the basic beam output calibration measurement. The Co-60 units utilized by the participating institutions were of differen tseee b Tabln origin i nn Mos. ca e3 thef s o t,a m were calibrated by the Comision Nacional de Energïa Atömica of Argentine at the tim sourcf o e e change CNEe .Th A use thesr sfo e purpose sdosimetea r with appropriate chambers calibrate r SSDLou .t da The intercomparison results are summarized in Table 4- Of 14 intercompared units, 9 have a satisfactory dosimetry with a deviation lower tha ')%.n+ Four centers hav deviatioea 10,«- n.d betweean ° 5/ n- Only one center delivered a dose lower than that required.(beyond — 10?o).

TABL . E3 IRRADIATO R TYPES

Code Irradiator type Dat lasf o e t number Bourse's change

110 Theratron 780 April 1975 112 Picker November 1973 120 Picker - 121 Picker (Cs-137) - 122 Theratron C September 1975 124 Theratron Junior July 1974 130 Theratron Junior January 1978 140 Siemens GainmatroI I n September 1975 142 Siemens GammatroI nII March 1977 150 Siemens Gammatron II March 1967 152 Picker - 160 Theratron Junior March 1971 180 Theratron August 1977 190 Whestinghouse February 1977

NOTE: Except code numbeirradiatore th l rCo-60f o al 121 e , .sar

48 «IP O r-- vO "3- c vD o t~~ 0 CM 0 -3- CM CM CM O I-. m to vO en CM CD to s 1 i + 1 1 + l i + to +

. r > > M 4-> Ul .Q !U r-- SOi O O o O 0 vO o c 0 O o 0 m O co 0) U O O o O o m o c o o CD o r-. 0 Z -H -H O CD o O o CM o CD o o CD o "3- CD en 4-O > < CM CM CM CM CM CM CM CM CM CM CV1 CM cj £&i3 ex (n •H

10 Q CO M l/l CO O oc 1^. CM M in T— 00 O r^ en «3- en r~.

8£ VO r» vo LT) in in VS CO VO o CD T 0 en en Ol O en CM CO co C co co O o CD <5= 4-•> Cù O i: -o o "Oo o ,j o m va t— \O VO r^- co •^T ro O co r- >* VO o ÎO L/î co ce r-. un es. ce oc 'S- cc to O IÛ

a O oo l/l I-O vO 0 0 L.O O en (NI P^ o , CO XI O CM VO •3- CO en «— 0 rrj- o L.O 0 •o (NI u~. O T3 T-* CM CO en CM to f. r^ co en en CNi

O c; Q, rs- r-. co •F*- LO \o O c: L/"> CD CD CO co o W *rt fT3 cn en en O en CM ce oo ô oo « CD c s g° 4J O •rH « CD •a < -O r-l r- co LO if. CTi LO r~- O (N! to O r~- co CM r~- M co en en r~- co to t^ ^* ^r m CvJ

10 Q< r- r~- LO o ir, ro i/i vO r~. r~ *£• CX! 'S- 10 cn en en o en CM ce CO o co co o o CD

oo ^"- LO LP. ^r i~- c-- cr. 0 'M -•ï- co en co CM vO VO t^. c-. 00 c; to 00 vO m 10 o •a- in o r- ce r^ o en to in i-3 CN) to rj «3~ CM to co C3 in en CO •K r^ in un in Lf> in in ro •sr LO in 'S- •«3- CM m ti M o U \D CM O •zr t~~ l.T •«• O ce CO ^r in o .a C in CO CM in ro en vC co CD CM CD co I-> T CD [-^ •a ij (3 10 CM to CM ro c-. o en CO •K r-- m CO LÖ LO u-, 3 in to *t in in «* "T CM m CJ « •a o fO u •o

CO LO VO ^r" o r- c CM en vO 0 vO 'S- vO CO CM r-» LO «c- vD o [^ 1O CM en 'S- VO c. & iH f- en (NI ^ T ^™ .-^ C5 rq VO o ^3- vC o 1-5 Ü II CM CM CJ in (SI fO er. C3 in CD co •«• t~. ^r in in LT. m L/l ro •»T LO m m T in CM L.O « * f-l IU Cl O .•M 0 (M ^? c c CM CD C^J 0 O 0 r- "Si CM (M CM CM to •«c -c- i/> in 0 co cr. O CJ 3 G 3.3 Discussion

The first national Intel-comparison gave a mean value of 196, 12 rad absorbee th r depthm fo dc 5 dos ,t ea wit relativha e standard deviation of +_ 4»3/£. With regard to the prescribed dose of 200 rad, the mean value deviated by — 1,9%« e intercomparisoTh n mad IAEA/WHy eb O from 197 197o 4t 7 gav meaea n absorbee th r depthm fo valudc d 5 dos197[f ra e,o t ea 2wit ha standar d deviation of + 4j4%. The mean value deviates from the prescribed dose of 200 rad by""- l,4/o.

3.4 Conclusions

The TLD intercomparison programme is a very important complement to other means employed to improve the accuracy of radiotherapy clinical treatments. ProArgentine th m e experienc D intercomparisoTL n ei n studies, this programm usefus ei onlt identiflo no y t y error d inaccuracsan y in the clinical delivery of radiation but to create a greater aaareness of the need for correct dosimetry in radiation therapy and to improve contacr ou t with radiotherapy center countryr ou n si . Many physiciank sas for advisor d calibratioyan n services interese th d gettinn ,an i t g better accurac dosirnetrn yi s increasedha y .

. 4 FUTURE INTERCOMPARISON PROGRAMME

In the future this laboratory will continue with the TLD intercomparison programme for telegammatherapy equipment in the y indicatewa d above. recentle Th y initiated similar feasibility stud orthovolr yfo - tage X-ray units wil followee lb orden i d staro t rintercome tth - parisons as soon as possible. indicates A d above ferroue ,th s sulphate syste higr fo mh doses has been developed and we intend to apply this system to the radiotherapy dose rang carro et intercomparisot you n studies. The first linear accelerator for radiotherapy has begun to work this year in Argentina, and several others will begin in the near future. For this reason this laboratory wants to study an intercomparison programm r sucfo eh equipmen chemicae th t d usinan l D g TL bote th h syst ems.

REFERENCES

(1) H. H. Eisenlohr, S. Jayaranian: "IAEA/WHO Co-60 Teletherapy Dosimetry Service using maile dosimeterF Li d - A surve sre - f yo sults obtained during 1970 - 75" (1976). (2) H. Mugliaroli, R. Gonzalez, M. Saravf de F. Gianotti: "Activities with TLD in the Regional Reference Center (CNEA) - Argentina , 1791/RBo N C 1977R/ ,.

50 EXPERIENC INTERCOMPARISOEN I SSDA T NLA FOR ORTHOVOLTAGE AND HIGH ENERGY BEAMS

G. SUBRAHMANIAN, I.S. SUNDARA RAO Radiological Standards Laboratory, Division of Radiological Protection, Bhabha Atomic Research Centre, Bombay, India

INTRODUCTION

With the increasing use of high energy machines such as teletherapy units and high energy accelerators in the various radiotherapy centres in our country, the Secondary Standards Dosimetry Laboratory of the Bhabha Atomic Research Centr playins ei n importanga t rol attendinn ei e th o gt dosimetrie needth f so c requirement thesf so e centres. SSDL (Bombay) main- tains all the national primary standards for various radiation qualities. These primary standards have been intercompared with similar devices at the International Bureau of Weights and Measures (BIPM), the National Bureau of Standards (USA) Nationae ,th l Physical Laboratory (UK) Bureae ,th f uo National Metrology (France) and the Regional Calibration Laboratory (New York) during this decade intercomparisone Th . s have been carrie usint ou d g transfer standard Shonka chamber resulte th d san showed congruence better than centr SSDe pe Th L.1 provide- addition i s followine th n g services: (1) calibration of Secondary Standard Dosimeters belonging to various centres in India; (2) output calibration of radiation beams for field conditions; sitn i u ) compariso(3 l Instituteal f no sSecondar* y Standard Dosimeters against SSDL reference standard etc.; (4) organizing postal dose intercomparison programme using TL dosimeters for different types of radiations in collaboration with IAEA/WHO in this geographical region. The procedures adopted by the SSDL for such postal dose intercomparison programmes for teletherapy beams and our plans for the international intercomparison for high energy photon and electron beams and also our experience gained in this field are outlined in this paper.

Since 197 SSDe 6th L Bomba beed yha n conductin absorben ga d dose intercomparison service for Co teletherapy units in India, Burma and Sri Lanka. Abou dos0 7 t e intercomparisons have bee radiotherap0 5 n t conductea r fa o ys d centres resulte Th . seee summarizee b sar n y ma fro e t I Tablmth n d i . e1 Table that in 69 per cent of the cases, the deviations were within - 5%.

Radiological Standards Laboratory, Division of Radiological Protection, Bhabha Atomic Research Centre, Bombay - India.

51 The intercomparisons were repeated whenever deviations exceede 15%- d n .I most cases a significant improvement in dosimetry was observed on repeat intercomparisons. These intercomparisons had also brought to light some instances of serious errors in the dosimetry practices in some of the hsopitals. Wheneve serioua r s erro s detectedrwa , immediate follow-up action s initiatedwa d this continue,an swa d unti mistake lth s identifieewa d an d rectified e postaTh . l dose intercompariso d thunha s really averted several potential accidents in radiotherapy. Frequent intercomparisons are very importan assuro t hospitale eth continuef so d adequac n theii y r dosimetry and in some cases to detect if any later mistake had developed. Thus the dose intercomparison service is valuable both from the point of detecting serious errors and ensuring uniformity and good quality of radiotherapy dosimetry.

An important extension of radiotherapy dosimetry service is the provision of accurate beam output calibratio teletherape th l nal datr yfo a units because the accurac n dosi y e calculations mainly dependaccurace th n o sbeaf o y m output value. This programm s initiateewa d conductean d d concurrently wite th h dose intercomparison service by deputing a senior physicist of the SSDL to various radiotherapy centre e countryr countryth ou n n i sI .o far ,s , there io officiasn l cod practicf o e e specifyin beae th m w outpugho t measurements should be performed. Most of the hospitals measure the beam output in air at SSD + 5 mm. Some hospitals measure the dose directly in a water phantom at 5 cm depth. However, almost every hospital relies heavily on published data percentagr fo ) (1 e depth dose, back-scatter factor etc., require absorber fo d d dose calculations e SSD s consciouTh .Lwa e facth t f o sthadepte th t h dose value e influencesar somo t d e exten machiny b t e parameters suc s sourca h e size, secondary collimator design, penumbra trimmer d radiatiosan n field size specifications vis-a-vis optical field etc. Bearin l thesal g e thing minn e i s th d visiting SSDL physicist performed beam output measurementn i d an r s ai bot n i h phanto eventuar fo m l compariso absorbef no d dos watern i ee resultTh . o s far obtaine 0 teletherap5 r fo d y unit ss foun werwa t dei thaanalysed an t ) (2 d the absorbed dose value calculate methodo tw y usin db e sth g differes a y db much as 4% in the case of eight units. Again for these eight units percentage depth dose was measured by exposing TL dosimeters at both 0.5 and 5 cm respectively e deptTh . h dose values differed from those publishee th n i d British Journal of Radiology (Supplement 11) by as much as 2.8 per cent (3). The percentage depth dose is an important parameter for clinical dosimetry and should be determined experimentally. The published data may be used for totar fo guidanc lt relianceno t ebu . This experiencanotheo t s u rd le e extension of the dosimetry programme namely the central axis depth dose data servic mailey eb d dosimeters n irradiatioA . n stand designe o thaD s d TL t capsules could be inserted at eight different central axis locations was maile eaco t d h participant along wit n adequata h e numbeD capsuleTL f ro s depending on the demand by the radiotherapy centre. The irradiated capsules were measured at our SSDL and the results communicated to the user. The depth dose measurement service is entirely independent of the dose intercomparison programme s interestini t I . noto t g e that when error n deptsi h dose

52 values use n intercomparisoi d n were correcte measuree basie th th f so n do d depth dose value, the results in some cases have shown significant improvement.

2. Orthovoltage X-ray dose intercomparison

e situatioTh othey an Indirn n ni i developins a g countr thas e i y th t annual growth rate in the number of teletherapy installations is quite rapid while mor mord ean e conventional X-ray therapy unit e lyin sar disusn i g r fo e obvious reasons. Henc neee X-rar eth fo d y intercompariso keenlo s t yno s ni 60 teletherapyo C case th f eo n i fel s .a t However SSDLe ,th , Tromba worked yha d methodo outw t qualitr fo s y determinatio ratiL T y namelon- b ) centra(1 y l axis depth dos ) externae (2 rati d oan l filtration. Botmethode th h s have been proved to be independent of X-ray spectrum for a given first HVT. They have been successfully use preliminarn i d y dose intercomparison experiments conducted for superficial and deep X-ray therapy at a local hospital.

mose Th t important factor that mus consideree tb n thii d s contexe th s i t large fluctuation in X-ray beam intensity due to main voltage variation in citiese th man f yo . Froexperiencr mou have ew e noticet no d s i tha t ti uncommon in routine output measurements that a set of 5 successive output measurements each of 2-3 minutes duration showed variations as much as - 10%. Is impossiblti statemena relo et n yo deliveref to d dose unles X-rae sth y unit had incorporated a monitor chamber system. This point is very important in X-ray therapy dosimetry, particularly when a recommendation has to be made to a hospital on the factors that caused larger deviations. To the best of our knowledge none of the X-ray therapy units in India had built-in dose monitors vien I this.f wo programme ,th initiato et e regular dose intercomparison service to hospitals was deferred in favour of developing a reliabl d simplean e monitor syste eventuar mfo l large scale supplo t y hospitals. The SSDL has succeeded in developing a small ionization chamber that can be positioned near the space provided for filters.

importann a s i T tHV paramete X-ran i r y dosimetry measuree Th . d value of HVT depends on the conditions of geometry, purity of filters, energy dependenc detectorf eo s etc. Excep purposer fo t usinf so g published depth dose data, the HVT value is not required in dosimetry. Instead of HVT in aluminium or copper, half value depth in water would be a better specification of beam quality. We think that the most appropriate dosimetry service for orthovoltage X-rays centrar shoulfo e db l axis depth dose values using mailed TL dosimeters. The HVT as well as the absorbed dose at a specified depth (5 cm) can be obtained simultaneously besides the central axis depth dose data.

3. Dose intercomparison for Megavoltage X-rays

largA e numbe medicaf ro l accelerator worle s th use dn i de belon th o t g less photo V thaM 0 n1 n energy category (4)encourago T . e participatiof no many hospitals, the dose intercomparison service may be restricted to 6 MV only for the time being. Another advantage of choosing 6 MV is that the existin dosimetro C g y servicextendee b n eca d easily powdeF Li . r encapsulated in nylon is adequate at this energy. A check on the beam energy is very

53 important to avoid errors in dosimetry and this can be done by depth dose ratio check. Since the accepted calibration depth up to 10 MV is 5 cm, two dosi- depthm c d irradiate0 1 an s d an m meterlocatee c b d 5 y simultaneously t sma a d . e dosTh e intercomparison servicextendee b y ema higheo t d r energief si necessary in a progressive manner. The depths at which dosimeters should be locate calibratioe th dsame s th musa e e tb n depths recommende y ICRdb 3 2 U beyondm c 0 1 .d an V M 5 2 o t p u m i.ec 7 .

4. Dose intercompariso higr nfo h energy electrons

IAEA and many other standard laboratories have been conducting electron beam dosimetry service by mailed Ferrous Sulphate dosimeters and valuable experience has already been gained on the reliability of this service. There IAEe discontinuo th t A neeo i r n s fo d e this servic d finean d another substi- tute for FRICKE. The FRICKE system is recognized as a secondary standard and proved to be stable and reliable for mailed dosimetry. From the point of convenience the intercomparison service should be restricted to one electron energy, say 20 MeV, and the depth of measurement should be in the region of dose maximum (1.5 cm).

n energA y check measuremen dose t th parmusa e f e intercomparisono tb . This check can be done by irradiating another dosimeter at 3.5 cm depth simultaneously.

In conclusion, it must be said that absorbed dose intercomparisons have proved extremely valuabl n improvini e qualite th g radiotherapf o y y wito C h and orthovoltage beams. It is only appropriate to extend the programme to include high energy photon and electron therapy. For the sake of completeness, 137Cs teletherapy must also be included in the dose-intercomparison.

Table 1

Result Postaf so l Dose Intercomparison

Batch Total Institutes who returned % 15 ±5 %% 10 5% capsules

1 5 3 2 - -

2 8 5 31-

3 10 5 521

4 9 7 2 - -

5 15 8 733

6 22 15 753

Total 69 43 26 11 7

% 38 15.5 % 62 % %10 100%

54 References

(1) Central axis depth dose data for use in radiotherapy Brit.J. Radiol., Suppl. 11 (1972) (2) S.B. Naik, I.S. Sundara Rao and G. Subrahmanian, Beam output calibration of teletherapy units. AMPI Medical Physics Bulletin 4, 1(1979) 23-25 (3) T. Malini and PNMR Vijayam (1978) (Unpublished). (4) Directory of High Energy Radiotherapy Centres (1976) IAEA.

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55 BUREAU OF RADIOLOGICAL HEALTH ACTIVITIES IN DOSE DELIVERY SURVEYS

. MORTOR N Radiation Therapy Branch, Bureau of Radiological Health, Rockville, Maryland United State f Americso a

1. The Bureau of Hadiolorical Health (3:Gi) is part of -the Food and Drug- Administration of the Unite! States of America and is responsible for the safe and effective use of radiation from electronic products and radioactive material. Licensing the radioactivf o e us e by-product material remain respone sth - sibility of the Nusiear Regulatory Commission.

. 2 Between 197contracteH d 197ER 4an e 7th d witNationae th h l Bureau of Standards (NES) of the United States to conduct a dose delivery cobalt-6e surveth f yo 0 teleiha-spy units . Thi s similaUS IAEe swa e th ith A no t rposta l dosimetry service, but on a one time basis. Abou) abouf a unito 0 t 11 t sou 100 0 units were surveyed. b) 83 °j» yielded dose interpretations within 5 °j, of the prescribed dose. c) 13 fi yielded difference between 3 "jo and 10 $. d) /, •£ of the dose interpretations were creator than 10 ,' for the dose requested. e) N3S Technical Note 978 is a publication reporting the d othersan result e surveK th BR . e f st o y BR!) f conductin!s i n analysiga e survo th wil d f san yo l publis conclusions it h y latsb e summer 19"'9. g) An "Interim Report of the National Bureau of Standards/ Bureau of Radiological Health Co Telcthorapy Survey" by Thompon, Wyckoff and Soares appeared in Int. Journal of Radiation Oncology, Biology and Physics, (Vol 4 pp-106^- 1068 Nov 1978)c -De - plannins i H BR 3mailega . d dose delivery surve medicaf yo l linear accelerators with photon energie^ î 0 1 s o frot ) / m

a) N13S will evaluate and calibrate a lucite phantom containing LiF - TLD chips.

57 b) BfiH will conduct the survey probably using LiP - TLD chips because of considerable experience in handling large number of these chips in surveys of dental and mammographie X-ray units. c) An advisory •jroup from the Radiation Therapy Committee of the American Association in î-iedicine is assisting in the desig d selectioan n dcsimetr e th f o n y syste d wilan m l hel plao e t psurve th n y questionnaire. deliveree b dose o th e survet e r Th fo ) s expectedd i y k as o t d ) lucitcm 0 e(2 r phantoa fo n i d n an me t0 depta o1 f o h the calculation arid constants used in arriving at that dose. This will provide rr.ore data than a simple dose interconparison in that it will also check the ability to deliver a prescribed dose under patient-like conditions. e) Site visit follow-up is planned in cases where serious dose delivery difference is found. 1) Tne serious difference "level"has not been defined. methoe Th follow-uf ) o d2 beet ne n s decidedpha . Possibilities include: Hirin) a g private consultants. b) Forming an agreement with the six Centers for Radiological Physics whic e sponsorehar e th y db National Cancer Institute and coordinated by the American Association of Physicists in Medicine.

planr-Scs i t I offeo t ) Lavailabl e f rth D doseTL e delivery assessmen continuina s ta g programme that could become part o ffacilitiea s comprehensive quality assurance program.

y reasonM attendinr . sfo 4 g this meetin thae questione gar th t s the IAEA needs to answer for an intercomparison of medical linear accelerator members s needK it BR a o solvf st e o sr ,th fo e similar Unitee surveth f dyo States. Further botf ,i h agencies choos same compatablr eth eo e survey methods, we both will have an expanded data base.

58 STATU RADIATIOF SO N THERAP NIGERIYN I A PROBLEMD AN ACCURATF SO E DOSIMETRY

A.O. FREGENE Dept Radiatiof .o n Biolog Radiotherapyd yan , College of Medicine, Lagos University, Lagos, Nigeria Abstract: The status of radiation therapy in Nigeria, a developing nation, and high-light f canceo s r incidenc Nigeriann i e e presentedar s . The need to develop radiotherapy, and its place in relation to other moralities of cancer management in developing nations are examined. Finally, the numerous problems of radiation dosimetry typical of some developing nations are stressed. In Lagos we place emphasis on the FeSO, dosimetric system for the most reliable results. In view of the numerous weighty problems in developing nations, there is need for a continious input from the developed nations in order to build-up the most effective radiotherapy centres.

Introduction fl) It is difficult to discuss the Status of Radiotherapy in Nigeria and the Problem f Accurato s e Dosimetry withou w wordfe a ts abou e pattern.th t , of cancer incidence in the country. In additio e establisheth o t n d fact d speculationan s n respeci s f canceto r incidence- racial, sex, age etc., and aetiology in man- genetic, environmental, viral, n importanetca . t finding worth statin thats i ge over-al th , l crude incidence of cancer over the last several decades in Nigeria, is significantly lower than that in Europe, and the U.S. (Doll et al. 1966). Cancer incidence survey Nigeriann i s Edingto( s Haclead an n experienc r ou n d 1965an )Lagon i e s ovee lasth r t decad whicn i er Radiotherap ou h y cente s beeha rn functional, confirm this trend. Virtually, all types of cancer seen in Caucasians have

59 been recorde n Nigeriani d t prevalencbu s f specifio e c types differ e onlTh .y Radiotherap e cit yf th Lagoso e centryregion i th n s ,i i en populatio million3 n . This centre receives cases of cancer referrals from all over Nigeria (population 90 million) and also from neighbouring countries, the Camerouns, Ghana, and Sierra Leone. In discussing the incidence of cancer in Nigeria we cannot but mention a w unusuafe l findings whic y havma h e some implication e generath r lfo s cancer effort. ) (a Primary cancee lund liveth an e glinkef ar o r d respectivelo t y smoking and excessive alcohol consumption amongst other causes. Both practices in Nigeria for economic and other reasons are indulge o considerablt n i d y lesser extents than amongse th t developed nations e incidencTh . f primaro e y lung carcinomn i a Nigeria is unusually low, - only three cases amongst some 1,000 cancer patients seen in Lagos. Liver cancer incidence on the other han s reportei d d higher than amongst Caucasians. ) (b Another occurrenc e unusuallth s i ew incidenclo y f e canceo e th n i r aged in Africans, Davies et al. (1962) - considerably less than in Caucasians - it would appear that those who escaped the multitudinous infections and disease afflictions in childhood and middl e develoag e p enough resistanc o combat e t d canceageol .n i r (c) A common occurrence in both Caucasians and Nigerians is that the incidence of Ca-Breast and Ca-Cervix is high. Indeed about 2 out wome3 f o n treate r r radiotherapcancefo ou d n i r y departmene ar t either afflicte y Ca-Breasb d r Ca-Cervixo t .

) Radiotherap(2 y Centre n Developini s g Nations The problems encountered by developing nations in respect of effective applicatio f radiatioo n n therapi n e manifoldar y ; where facilitiee ar s available e.g. in Lagos, we find problems of (a) lack of supporting technical personnel for effective maintenance and service of teletherapy machines. ) (b mulish ignoranc f administrativo e e staf d consequenan f t inertia in financing progressive programme e areath f traininn o si s d an g acquiring of accessory equipment.

60 (c) with a one man band therapist, possibly one trained a couple f decadeo s back, arid limited clinical interactions with other radiotherapists, chance f optimisatioo s f radiotherapo n y service are not enhanced. (ci) the status of the general radical service whic.n is rerrotely tied e leveth f cenceo o lt p u r consciousnes f the-o s populace coule! effect cure r?tes; for instance, the over-all survival of our cancer patient n Logosi s , woul e inp'-cveb de ratheth f i 1d- high proportion of cases reporting for the "irst time in our clinics did not cone too l~t of a compact Radiation Centre, which incorporate!- a Radiation Biology section, Nuclear Medicine service and a Medical Physics unitr radiotherapOu . l y al divisio y b a siral e s i non l

rri standards s equippei t i , Theratroo d C wit a h unit 0 3 n c'-tliovoltag2 , e X-ray

machines a superficia d an , l X-ra e yaverage th unit n a gooO .n i d , yeef o r

m i UMin ! technical problems, roughly SCpatientw One e treatedar s e otherth , s

unfortunatel turnee ar y d away: thi i !.s - inevitabl numbee th n viei e f f o wo r

countries and the roainiiioUi sized population served by the centre.

(4} T_he Problrii Dosiiv.et.r_ ^of n i Legoy s

The prob le- :".:, of do s i nx-try in Lar.os are considerable, and the need for a

Secondary Standards Dosi^c'Lry labore tory canno oveo b t r estimated especially

in view of r lens 1.o esios'ish new '.r.erapy con ties net only ir. N ice r is hut in

neighbouring countries as well.

Firstly e performancth , ccii'inerciae th f o e l thimble chamber ove a lonr g

period in i.E.rnr is subject to fluct-.JSi.ionb owing to high humidity and temperature

conditions. Kifi Boon arc! colIcïcuss in Singapore a town v.ith high hu:::idity,

and similarl "lyinw lo y g tropical condition s Lagosa s , reporte e interferencth d e

of fungal growths as well (person: conrcvnicctio'i). They have, by proper air 1 pur ificetinn zr.d teiiperctu-e control (net conventional air conditioning)

61 established reasonable storage condition d consequentlan s y improved their ionisation chamber performance. In Lago rele vi sy extensively e FeSOth n .o , dosimetric system whics i h not affected by high humidity and fungal growth. Furthermore, we have for use as standards a pre-calibrated (NPL) 90Sr source, and our 60Co machine of predictable output. These ensure independent r checkionisatioou n o s n chamber measurements d e largeconfidenan ar y e B ,w . t thae prescribeth t d dosen i s contradistinctio e knows e on idea th y - o lan what ne f s one ideai i tar - s- l delivere e tumourth o t d. y pose questionma th ee e introductioOn th s i » f radiotherapo n y departments into developing nations justifiable? Skeptics may argue the importance of other prioritie n healti s h car n thesi e e emerging nations e.g e scourg.th f o e infectious diseases; problems encountere e numerouar d d weightyan s , e.g. lack of trained personnel to successfully execute the specialised damands of this sophisticate f modero m ar nd medicine etc. However, lookin n depthi g , would reveal a pressing need for the benefits of a radiotherapeutic service, even a modes f o te b sizet i .f i

(5) In conclusion may I state the following, (i) Cancer research and treatment in developing nations should be encourage t onlno dy becaus f theio e r benefit o thest s e nationst bu , alse possiblth o e benefits thae over-alth t l cancer effor y derivtma e from this completely different dimension; differences in geographical distribution pattern of cancer, e.g. Burkitt's lymphom n Africai a ; variation n incidencei s e dependenceag d an , , which could a modificatiolea o t d r evolutioo w , conceptne of n f o n s e aetiologith n d treatmenan y f cancero t . (ii) Dosimetry in developing nations, is confounded by numerous factors, d cooperatioan n wite largeth h r centree developeth n s'i d nations can only enhance performance. (iii) Radiotherapy in developing nations is at its infancy and may be nurtured fully only throug e inputh hf boto t h economical, technological and human resources from the better developed nations.

62 (iv) In view of the acknowledged advantages of radiotherapy over other modalities in the treatment of certain types and forms of cancer, and obvious general limitations in developing nations, in these areas as well, e.g. experienced manpower, facilities in the effective administratio d folloan n w throug f chemotherapo h d evean yn surgery, in cancer management, a well developed and properly dispensed less traumatic radiotherapeutic service has a lot to commend it in developing nations.

References:

d Maclea) Edingtoan (1 . M n . 6 C.M.Un . Brit. J. Cancer 19 471-481 (1965) d Knoweldean ; ; Wilso) A. DaviesP. (2 . J . . nB N n . J , Lancet (ii 8 (196232 ) ) (3) In Cancer Incidence in Five Continents; A Technical Report; distribute e Internationath y b d l Union against cancer. Edited by Richard Doll; Peter Payne; and John Waterhouse. Springer - Verlag Berlin - Heidelberg and New York. Boona Ki ; ) "Persona(4 l communication".

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63 USE OF THE FERROUS SULPHATE DOSIMETER TRANSFES A R INSTRUMEN CALIBRATINR TFO G CLINICAL DOSIMETERS

J.P. SIMOEN CHARTIER. ,M . PAGE,L S Laboratoire de métrologie des rayonnements ionisants, CEA, Centre d'études nucléaires tic Saclay, Gif-sur-Yvette, France

1 - INTRODUCTION -

In clinical dosimetry basie ,th c physical paramete reference th s i r e absorbed dose which determines the treatment durations and consequently the doses delivered to the patient. It has been shown, through systematic clinical observations, that discrepancies of only 10 '5 between doses delivered to tumours in identical treatments led to significant clinical differences, thus leading radiotherapists to wish for dose estimations with reproducibilities of . SucJ 1 accuracied h f an constraint 1 % 1 3 referenca f so f o e s us imple e th y dosimete higf ro h qualit correctld yan y calibrated.

Considering that dosimetric primary standards at national laboratories are usually defined with overall uncertainties close to 1 1, and that transfe- rence of knowledge through calibration of an instrument inevitably deteriorates accuracy obvious i t ,i s thaoperatioe tth calibratingf no dosimetryn ,i a s ,i delicatmusd an carriee t b e ewiton t dou h particular care. Note that this si seldom the case in other fields of metrology where the levels of accuracy between primary standard field san d measurements differ ofte y severanb l orders of magnitude. Moreover, the increasing utilization of accelerators in radiotherap enhances yha neee r calibrationth dfo d termn si f absorbeso d doso t e tissue (or tissue-equivalent materials such as water). Such calibrations can be deduced fro calibratioa m termn ni exposurf so applyiny eb g appropriate con- i i version factors (C» s /2 /, C s /" 3 J) ; but recent thorough analysis of " E these factors f 4 J have shown that their values could lead to errors of several percen and, t , besides, even with correct factors, this procedur ablt no e s i e to take into accoun actuae tth l irradiation condition whicn si calibratee th h d dosimeter is to be used. Therefore, the best solution consists of calibrating dosimetee th r directl termn yi absorbef so user'e th n dsi dosbeamd ean , provided that an appropriate transfer instruisent is chosen.

thiIs ti s last procedure whic bees hha n retaine recentld n dan i t ypu Frence placth n hei Calibratio transfee Th n . ChaiJ rB nf dosimete r choses ni the ferrous sulphate dosimete calibratioe th d ran n conditions were agreed upon following thorough discussions with medical physicists e procedurTh . s ei applicable to Y-rays from cesium-137 and cobalt-60 and to X-rays of maximum energies greater tha MeVn2 d -c,an o electrons with initial energies betwee0 1 n and 35 MeV.

65 CHARACTERISTIC- 2 FERROUE TH F SO S SULPHATE DOSIMETER-

e transfeTh r dosimete sealea s i r d glass ampoule containine gth ferrous sulphate solution (see. fig) 1 .

S°lution_containe- 1 - 2 r-

e containeTh pyrex-glasa s ri s ampoul cylindricaf eo l shape, with 1.5 mm walls, an outside diameter of 1.7 cm and a height of 6 cm. In order to avoid spurious oxidation while sealing the container, the solution is frozen by liquid nitrogen during this operation.

2 - 2 - Ferrous_sulphate_solution_-_

As the standard Fricke dosimeter, the solution consists of : 1 1 rn.mol.l~ (Ve

1 0.4 mol.l' H2S04 dissolve air-saturaten di d distilled water.

The distilled wate prepares i r thren di e stage normaa : s l distillation and two slow evaporations in quartz equipment using infra-red heating. Becausgreas it tf eo sensitivit organio yt c impuritie solutioe sth n mus préparere tb handled ,an d with particular care glasl .Al s vessele sar cleaned wit slronha g oxidizing solutio pre-irradiatedwitd nan h dose f severaso l kilograys. The water used for rinsing is the same as that used for preparing the solution.

2 - 3 -

Variatio ferrie th f nco ion, concentratio solutione th o n t ni e ,du irradiation, is determined by means of the absorbance variation of the solution measure y spectrophdb o tome try, accordin Beer-Lambert'o gt s law. Thue sth absorbe dsolutione th graysdosn i n i e obtaines ,i ,classicaD e th y db l SO J- formula : 6 ) (1 Q k x — —— — — — x 9.64= 10 . D9x sol e.Ç>.l,. G. U

where

e / (raol.l ) .cm is the molar extinction coefficient for ferric ions at the wavelength used for the optical density measurement ( \= 303 nm in our case) , minus that for ferrous ions, at the reference temperature (25°C) . _3 densite solutioe p/g.cth reference th s th f i yo t m na e temperature (25°C) 1 /cm is the optical pathlength of the spectropho tome trie cell. ) ± 0.0% m 5c 1 (1= G / (ferric ions). (100 eV)~ is the radiochemical yield of the ferrous sulphate solution.

66 & d is the difference in optical density between irradiated solution and blank, measure actuan n t da l temperatur usuall0 e y slightly different thae nth 25°C= referenc 0 . e eon o

k is the correction factor for temperature : 0

) (2 e- oe )( ) a + i C / i = T k

O O _1 with 0, 0Q in C and a in ( C)

Before utilizatio ferroue th f no s sulphate dosimete r calibrationsfo r , different properties and characteristics of the dosimeter as well as those of 1±e spectrophotometer have been studied. Among them, the values ofc » p r a have been determined :

= 216E 3 (mol.l"1% )" 1 1.cm"0. ± 1

p = 1.024 g.cm" i 0.1 S,

a = 0.66.10"2 ("a"1 r. 1.5 %

Cbncernir. valueG e th g, which depend radiatioe th n so n qualitye ,th following convention has been adopted with users : until the end of the ßxperiments carried out at LMRI and at other foreign laboratories for the determination of G values in high energy photon and electron beams, a constan : adoptes t/ i valu5 G / df eo

G - 15.6 i 0.25 (I'fe"3 ions). (100 eV)"1

This convention, though perhaps leading to false reference doses, enables however comparisons between hospitals throughou countrye th t . Nevertheless, this assumption shouldn't be too bad if one considers the G values indicated in ICRU. J report3 , 2 s/

TRANSFE- 3 R PROCEDUR- E

- 1 - 3

o calibratioTh performes ni user'e th n si d beam conditionn ,i s clossa e n.G oossible to the usual ones (this is of particular importance for accelerator beams dosimetee Th )calibrate. e b transfee o rt th d an dr dosimeter successie sar - vely irradiated under identical conditions ,same i.eth e r inciden.fo t bead man same n.th te positio referenca n ni e water-equivalent phantom. The reference quantity is absorbed dose to water, D /Gy ; the calibration -1 factor, F/Gy . (unit of dosimeter reading) , is given by

dosimetee th whers i eR r reading, correcte r dependencdfo n o e temperature, pressure, humidity, recombination, etc...

67 M and M are the monitor readings, corrected if necessary as above; in the case of a Cobalt-60 or a Cesium-137 beam the monitor is simply a time measuring device.

e referencTh e dos wateo t e , rD is obtained from the dose D , measured W sol e ferrouinth s sulphate solution (relatio applyiny b ) 1 n factoga rk correctin g perturbatiovolume e glasth th e size th f solutiof th r e o o s o fo o t t d e nan du container :

(4) DW = °sol

value G e samconvens i choicth e e e th th r ,k reason f r Fo -eo fo s sa P tionally taken equal to unity until its experimental determination.

3 - 2 - General conditions -

Some of the calibration conditions are standardized, they are presented tabln i . 1 e

- dimensions : 30 x 30 x 10 (cm) - water-equivalent composition : 94 % polystyrene PHANTOM 2- polymerizatio% 5 l noi 1-3 % T.O

- density : 1.03 g.cm

REFERENC, 5 , 4 E, 3 DEPT, 2 : H 6 cm

FIELD SIZE : 10 X 10 (cm)

DOSE TO BE DELIVERED : 50 to 100 Gy

Table 1 : Standardized calibration conditions

The water-equivalent phantom is composed (see fia. 2) of five parts : F, f, A1, B. The main part F contains a cavity into which the other elements e wholTh e 4 constitutet fi homogeneousa s parallelepiped, excep r elementfo t whicf h contain dosimeterse sth givea r n.Fo beam quality reference ,th e depth is obtaine orderiny db . (se B , eelemente figA' g th , A .) 3 , sf

For each calibration, three elements "f" are provided : - two containing each three ferrous sulphate dosimeters (see. fig. 4) : one for irradiation, the other for blank, - one for irradiation of the dosimeter to be calibrated.

68 Particula- 3 - 3 r condition_ s-

The source-to-phantom-surface distance is chosen by the user. The reference depth depends on the beam quality :

- for cobalt-60 and cesium-137 gamma-rays and for 2MV X-rays, the recommended referenc. ecm dept5 s hi - for photons of higher energies and for electrons of energies between recommendee MeV5 th 3 , d 10an d reference dept e deptth hs hi correspondino gt the dose maximum determinee b ,o whict s preliminarhy ha db y measurements.

3 - 4 - Uncertainties_-

uncertainte Th calibratioe th f yo n facto rdependF course f so th n eo uncertainties on the readings of the dosimeter to be calibrated and of the monitor. Concernin reference gth e estimatee dos wateth o et , rD d upper bound to the systematic uncertainty is 1.9 % (linear sum of individual uncertainties) and the random uncertainty is usually of the order of 0.4. %.

RESULT- 4 CONCLUSIOD SAN N-

Thirty-two calibrations have been performed up to now. All dosimeters were of the same type (Nuclear Enterprise, lonex 2500-3, 0.6 cm chamber), and had previously been also calibrate termn di exposurf so cobalt-6r efo 0 gamma- rays. Hence, it is interesting to consider, for each chamber and for the different beam qualities dosquotiente e ,th th e f calibratioo 1 sC n factory sb the exposure calibration factor presentee ar value e ' .Th C tablr n f sdi o fo e2 photons and table 3 for electrons, along with indications on experimental conditions and, for comparison, with the ICRU recommended values of C^ and C f2, 37. For photons., it can be seen that C1 and C^ are identical for cobalt-60 gamma rays and for 5.5 MV X-rays and that important discrepancies appear for higher energies (the mean value of the quotient C'/C\ rises to 1.06). In addition correctioeffece e ,th th f to recombinatior nfo chambee th n ni r (less doesn') tha% 1 n t modif discrepanciese yth .

For electrons the differences between C's and C 's, particularly at high E energies, see depeno mt d correctionmainle th n yo recombinationr sfo , whicn hi these cases ris severao et l percen ove; mea e MeVt3 th 1 rn, valuee th f so thesf e 1.0i quotien0ar e C correction/ tC s have been applie notf 1.0d i .4dan

A conclusionsa , this transfer procedure provides more information than only the calibration factor, because all irradiations and measurements with the dosimete calibratee b o rt performe e n beams i d ar hi use e d n th ,an ri y db the cas acceleratof eo r beams influence ,th monitorinf eo takes gi n into account as well as the quality of the preliminary measurements necessary for

69 photon number dose rate depth in correction C (ICRU) quality of C' values rad .min phantom, cm for rad. R rad. R recombination

60C„o äv 7 0 20 50- 5 no 0.95 0.95 1.00

5.5. MV X 1 230 6 no 0.95 0.945 1.00

X V M 9 1 250 2 no 0.95 0.93 1.02

18 MV X 1 400 4 no 0.97 0.915 1.06

25 MV X 5 0 20 17 0- 5 no 0.98 0.90 1.09

1! 1 1.05 140 5 yes °'945 0.90 U 1 200 3 yes 0.98 0.90 1.09

X V M 7 2 1 40 4 yes 0.96 0.90 1.07

Table 2 - comparison of C' values resulting from calibrations of dosimeters and C, values given by A ——————•— ICRU-Report 14 /" 2 / (for convenience, quantities are expressed in non-Si units). electron beam number dose rate, deptn hi correction C1 C (ICRU) E energy 1 phantom for 1 -1 C'/C of C values rad.min rad.lT rad.R Ii McV cm recombination

10 £ 180/260 2 no 0.90 0.89 1.01

» 1 200 2 yes 0.8.8 0.89 0.99 II 1 245 2.5 no 0.90 0.90 1.00

13 1 50 2 yes 0.87 0.87 1.00

II 2 200/220 3 no 0.93 0.90 1.03

16 2 170/210 3 no 0.895 0.87 1.03 19 1 210 4 no 0.90 0.86 1.05

II 2 200 4 yes 0.865 0.86 1.01

II 1 200 5 yes 0.86 0.88 0.98

30 1 150 2 yes 0.82 0.81 1.01

Tabl - Compariso 3 e value1 C f o ns resulting from calibratio f dosimeterno C value d an s s give y ICRU-Repornb t ^_____ £j J (fo 3 2r£ 1 convenience, quantitie expressee sar non-Sn di i units). the choicreference th f eo e depth informationl .Al s relatiy experimentao et l condition measurementd san officiae th usee gives n i th i sr y lnb document sent back to the Calibration Center. After analysis of this document and reading of the ferrous sulphate dosimeters, the calibration factor is established Calibratioe byth n Center.

Becaus thif eo s distributio taskf no responsabilitiesd san ,gooa d co-ordination is necessary between the user and the Calibration Center. Moreover, this procedure constitute technicasa l assistance service, since throug relatione th h s with hospital physicists, many dosimetric probleme sar dealt with.

REFERENCES

- WAMBERSIE J al.1 t e f ,, Précisio,A. n dosimétrique requis radiothérapin e e Conséquences concernan performances choie le tl t xe détecteurs sde s- J. Belge de Radiologie, 52, 2 (1969)

- ICR J U 2 Repor / Radiatio, 14 t n Dosimetr X-ray: y Gamma-rayd san s with Maximum Photon Energ MeV0 y5 Betweed , ICRan 6 U n0. Publications , Washington D.C. (1969).

- ICR / U, 3 Repor f Radiatio, 21 t n Dosimetr Electron: y s with Initial Energies MeV0 5 Betwee d , an ICR 1 nU Publications, Washington D.C. (1972).

- ALMOND J 4 ,f P.R. SVENSSON lonizatio. ,H n Chamber Dosimetr Photor yfo d nan Electron Beams. Acta Biol. Therapy Physics Biology, 16, 2 (1977).

[ 5 7 - SIMOEN, J.P., et al., Transfert de l'unité de dose absorbée à l'aide du dosimètre au sulfate ferreux. Actes Ville Congrès Int. de la Société Française de Radioprotection, Saclay (1976).

72 e - sealeFig th Vie1 -f o wd glass ampoule containin e ferrouth g s sulphate solution

Fig. 2 - View of the transfer dosimeters and of the different elements of the water-equivalent phantom.

73 , \ f 1f

/\ X

^ -_-._^ L

c /\ F

f BAA Af BA Bf AA A BfA AABf

X/cm 2 3 4 5 6

Fig. 3 - Schematic top view of the phantom and orderings of its constituent r obtaininfo s g various reference depth. x s

- Fig Vie 4 f .elemen o w " containin"F t e threth g e ferrous sulphate dosimeters.

74 MEASUREMENT ASSURANCE STUDIES HIGH-ENERGF O Y ELECTRO PHOTOD NAN N DOSIMETRY IN RADIATION-THERAPY APPLICATIONS

M. EHRLICH, C.G. SOARES National Bureau of Standards, Washington, D.C., United States of America ABSTRACT

This is a brief review of surveys on the dosimetry of radiation-therapy e Nationabeamth y s'b l Burea f Standardo u s (MBS)S .NB e Covereth e ar d ferrous-sulfate (Fricke) dosimetry service, a recently completed survey carrie witt ou dh thermoluminescence dosimeters (TLDe dosimetrth )n o n i y cobalt-60 teletherapy beams a TLld plan ,an r )fo s surve f dosimetro y n i y high-energy bremsstrahlung beams.

1. Introduction e 197th 1t A IAEA Meetin n Nationao g d Internationaan l l Radiation Dose Comparisons, ' one of the authors (M.E.) discussed in some detail S involvemenNB e th whan s becomi t ha t e know s measurement-assuranca n e studies. At the time, our Fricke-dosimetry service, oriented mainly towards the uniformity of high-energy electron dosimetry in medical therapy, was about three years old. The author discussed its conception, rationale mechanicd ,an somn i s e detail d showean , d some test results. e servicTh s stili e l being performed, n face i numbe th t f participanto r s has increased from arouno ove t . Instea5 40 r1 d f repeatino d e th g discussions, which are available in the Proceedings of the 1971 meeting, a brief review is given in Section 2 of this report of some of the technical details of the NBS operation that were not discussed in the earlier report. Also, a progress report on the performance of the participant gives i sd plan an r nimprovement fo s n proceduri s e discussedar e . At the 1971 meeting, a possible future survey of dosimetry of cobalt-60 teletherapy sources, to be done with thermoluminescence dosimeters (TLD) s als,wa o mentioned. Since then e hav,w e complete a one-timd e voluntar ydosimetre studth f o y f oveo y r two-third e U.Sth .f cobalto s - 60 teletherapy sources. At present, we are working on the design and

75 calibration of a TLD system to be used in the near future by the U.S. Bureau f Radiologicao l Healt dosimetre a surveh th r (BRH f fo o y ) f U.So y . high-energy bremsstrahlung beams employe n radiatioi d n therapy. Since some e considerationth f o s going inte desigth o f surveo n y program f thio s s f intereso type ar e t independenD systeTL e f choiceo mth f o t , thee ar y include Section i d , althoug3 n e systemth h e differenar s t from that employed by the IAEA.

2. Fricke Uosimetry for the Survey of High-Energy Electron Beam Dosimetry Dosimeters are provided to users requesting assistance with comparing their absorbed-dose measurement n high-energi s y electron beams with thosf o e their peers e dosimeterTh . s consis f ferrouo t s sulfate (Fricke) solution i n ground-glass stoppered radiation-resistant quartz spectrophotometer cells enclose n polystyreni d e holders s show,a e participantn figurTh i n . 1 e s irradiate all but one of the furnished dosimeters to between 50 and 80 Gy to water (500 800d 0an 0 rad electrot a ) n energie sMeV0 5 betwee ,d an 5 n employin e irradiatioth g n geometry (field size, typd siz an ef phantom eo , position of dosimeter in the phantom) given in the Protocol for Dosimetry of High-Energy Electrons. (2) After irradiation, the dosimeters are r spectrophotometrifo returne S NB o t d c evaluatio e ferric-ioth f o n n concentration in terms of absorbed dose in the phantom, using the value for the radiation-chemical yield given in the Protocol. Inasmuch as the disturbanc e radiatioth f o e ne quart fielth y zb de spectrophotomete wallth f o s r cells is ignored (the same value for the radiation-chemical yield being used ove a widr e rang f electroo e n energies e metho)th d canno e considereb t d o providt e participantth e s wit a highlh y accurate calibratio f theio n r system; it simply provides them with an indication of how their dosimetry compares with tha f otherso t . The Fricke-dosimeter solution used by NBS consists of the following conventional ingredients:

0.001 M Fe(NH4) (S04)2> dissolved in

N H 2a S0O. 4, well aeratedd ,an 0.001 N NaCl.

76 Because of addition of NaCl to desensitize the system against organic impurities e recomme,w e belo us n absorbed-doss wa it d e rat f abouo e t 103 Gy/s (10 5 rad/s), since NaCl causes an increase in the rate dependenc e radiation-chemicath f eo l yield. A simplified reaction mechanism (withou e NaClth t s showi ) n below in orde o - reminentert 0 r e w readeth ho ds f into re reactio th o d an n determine e F syield ' . Fe++ + OH -> Fe+++ + OH"

2 H0 * • 2 0 + H

ii _i_ r i " HO + e F > - 2 H0 + Fe + H> - 20 2HOH "+

++ +++ " FeOH H+ + 2 Fe0H > 2O - + A fresh batch of Fricke solution is prepared prior to each shipment and decanted inte individuath o l dosimeter cells. Rather than using glass vials, we find it advantageous to use the stoppered spectrophotometer cells in which the optical density of the solution is eventually measured. e glasTh s vials woul e lesb d s costl d directlan y y scalablee th t bu , solution would have to be decanted into spectrophotometer cells for readout e havW . e shipped Fricke solutio e samth en i nspectrophotomete r cells for the past 12 years, with an attrition of about 20 percent only, during this period e relativ,th e standard deviatio e averagth f o ne reading thesn i s e cell f irradiateo s d Fricke solutio s increaseha n d fron, about 0.8 percent to a still satisfactory 1.2 percent, probably because f smalo l nick r scratcheo s e celth l n i swalls e thereforW . e consider e initiath l larger investmen n spectrophotometei t r cell o havt s e been worthwhile e majoon re Th disadvantag. f usino e n unsealea g d systes i m the necessity of ensuring shipment at low altitudes or in pressurized plane compartments in order to prevent oozing of the liquid and loss of oxygénation. We initially cleaned all spectrophotometer cells with detergent in an ultrasonic cleane d froan r m the n kepo n t them filled with Fricke solution. All other glassware was initially cleaned with hot concentrated sulphuric acid sincan d e thes beeha nn kept filled either with Fricke solution or with pure distilled water. No plastics are ever in contact with the Fricke solution. We now produce our own organic-free distilled

77 water, in a permanganate distillation operation. ' We measure the change in optical density spectrophotometrically at the conventional 304 nm absorption peak of Fe+++ and from it determine absorbed dose to wate publishea vi r de radiation-chemica valueth r fo s le ferrous yielth f o d - ferric oxydation reaction e radiation-chemicaTh . l yield,s i G(F , ) e define e numbee F th . f s ionExpresseo a rdeV s0 forme10 n r i d pe d terms of molar concentration, M (mol/1) and absorbed dose D (Gy), this relationship becomes:

(1) G(Fe+++) = 0.942583 x 107 M/D ,

if the mass density of the Fricke solution is taken to be 1.024 g cm~ . Optical (transmission) densit . Transmissio nm measures i y4 30 t a d n density corrected for losses through scattering in the optics of the spectrophotomete s usualli r y called absorbance , whic,A y Beer'b h w la s is relatee molath o rt d concentrationy b , ,M

(2) A = e M d,

where d is the path length through the solution, in centimeters, M is e molath r concentratio e molath s ri molen i extinctionr e lite pe sd an r n coefficient. If one combines equations (1) and (2) one obtains

(3) D = 0.042583 x 107 ——————— Ae G(Fe+++)d

e changth s absorbancn wheri i e A A e e befor d aftean e r irradiatioe th f o n solution, and Ae ^e(Fe ). We initially chose to do our spectrophotometry at the conventional wavelength of 304 nm but may in the future decide to switch to a readout at 224 nm. ' The advantages of spectrophotometry at 224 nm are (a) an extension of the useful absorbed-dose range (about 5 to 350 Gy) to doses lower by a factor of about 2; and (b) a smaller dependence of the molar extinction coefficient, e(Fe ), on temperature (0.13% per °C). Prior to switchine woulw , dnm o verifreadout 4 g 22 yt a t that t thi,a s wavelengthe th , extinction coefficient of Fe is neglibly small compared to that of d that a consequencean s m ,a n 4 equation i 30 e t A ,a ) s (3 i n t i s a , Fe still can be set equal to e(Fe ).

78 For spectrophotometry to yield sufficiently accurate results, the following parameters e checkedb hav o t e : ) Wave-lengt(a absorbancd an h e scales provideS NB . r thifo ss purpose standard reference filter liquidr so quartn i s z cells ' Sinc. e aqueous potassium nitrate has an absorption peak at ^ 304 nm, it may be used for day-to-day checks on wavelength stability and absorbance-scale linearity.

i ii (b) Molar extinction coefficient, e(Fe ). While values for this quantity are given in textbooks, it is advantageous to determine it experimentally for one's own instrument and operating conditions, particularly because of its relatively strong temperature dependence and also because of the possible deficiencies in the optics which, in some instruments, cause its valu o changt e e with absorbance level. This determination involve e carefuth s l preparation of FeJ.J.J . solutions of a number of different known molar concen- trations, starting with electronically FrickeS purifieNB e -th dn I iron ' . dosimetry service, absolute dose determinations of high accuracy are not attempted; therefore absolutn ,a e determinatio molae th rf no extinctio n coefficient actually is not required; yet, it still is necessary for us to determine whethe e extinctiorth n coefficien constans ti t ovee absorbancrth e range of interest. One of the main features of our procedure is that we pre-irradiate all dosimeters, giving about 50 Gy (5000 rad) of cobalt-60 gamma radiation and using only dosimeters whose performance proves satisfactory.(8) Inasmuch as there is absorbance growth with time after preparation even in the dosimeters with satisfactory performance, AA in equation (3) has to be correcte r growtfo d h between preparatio d readoutan n , particularly since, becaus f delayo e dosimeten i s r returns fro e participantsm th som f o e e th , time between initia d fina an lweeksx le ordesi r th readouFo f .ro f o f i t this correction, we use the average growth on all unirradiated controls (shippe d unshippedan d ) whic e finw h d add t leasa s 1 percente tota th lo t uncertaint r procedurou f o y e because growt differens i h r differenfo t t cells. e overalTh l uncertaint r dosou en i ydetermination s currentl s takei y n aboue b o percent4 t , which coul decreasee b d morf o e dus readile th y b y thae dosimeteon n r measuremenpe r mora ty eb poin uniford an t m growtn i h absorbance from cell to cell between the readouts before and after irradiation by the participants, as might be achievable in a controlled

79 sealing procese typth ef o sdiscusse e nexth tn i dparagraph e quoteTh .- un d certainty does not include the systematic uncertainty caused by the assumption of a constant G value over the electron-energy range unaffecteV Me e presenc0 5 quarte th o froth y t b d f 5 mzeo cellsr ,o cause y non-uniformitb d e absorbeth n i y d dose ovee 1-cth rm e deptth f o h dosimeters' sensitive volume. Over the years, we have come to regret that we started with an un- sealed syste s operationa spitn it i m f o e l advantages, sinc a eseale d system may offer better stability. For this reason, we are now investigating the use of seal able spectrophotometer cells with necks graded from quartz o Pyret x glass, filled with Fricke solutio d sealedt weri an n ef I possibl. e o product a batce f suco h h dosimeters tha relativels i t y f stablo d an e uniform sensitivity r manfo yt i e successivcoul ,e on us d e irradiationd an s dose evaluations, particularly in conjunction with an up-to-date stable and sensitive spectrophotometer and readout at a wavelength of 224- nm, which might make it possible to go to lower doses and nevertheless decrease measurement uncertainty. We also have been discouraged by the relatively small improvement in e overalth l performanc e participantsth f o e e conside w e result f th I :l al rs obtained in the years from 1967 to 1975, we find that over 40 percent of the doses assigned by the participants differed from the NBS dose interpretation by more than 5 percent. These results are shown in figure 2. The improvement, if any, among regular participants was small, at least up to 1975. However, during the last year or two, considerable overall improvement was observed. In the last survey, the dose assignment of only 16 (or 24 percent) of the 68 dosimeters irradiated differed from the NBS dose interpretation by more than 5 percent. This is an encouraging sign of an increased awarenes e radiation-therapth y b s y communit e importancth f o y e f carefuo l dosimetry e hopW .e contributin ar tha e w t t leasa a g o t t small exten o thit s awareness. 3. TIP Systems for Nationwide Surveys of Cobalt-60 Teletherapy and High-Energy Bremsstrahlung Dosimetry 3.1 Cobalt-60 Teletherapy-Dosimetry Survey The cobalt-60 teletherapy survey was a one-time endeavor supported in part by the U.S. Bureau of Radiological Health (BRH). We mailed TL

80 dosimeter U.Sl al o .t s user f telethorapo s y d expressesourceha o wh s d their willingness to participate. Figure 3 shows the commercially available hermetically sealed dosimeter bulb containin a heateg r stri d smalan p l plaques

of the CaF?:Mri TLD material, which for shipment was enclosed in a suitable plastic container. While this system is initially more expensive than TLU powder or bare plaques ("chips") of the TLD material, it can be handled by a technician wit o previoun h s experienc n thermolurninescenci e e dosimetry. Also, since no large variations in source spectra were expected in the teletherapy survey, it was decided to use the CaF„:Mn phosphor which in th d foune ha paso perforn t de w t . reliabl d whican y h often canno e useb t d because its atomic number is higher than that of water and tissue. The readout system consisted of a commercial unit containing the heater- pholomul tiplier assembly, while general laboratory equipmen s user wa tfo d timingr integratingfo d ,an , digitizin d recordinan g e signalth g . With dose interpretation fro average e readingth mth dosimeters5 f o en o s n ,a overall uncertainty of about ?.5 percent was attained. This includes the uncertainty introduced by the need for correcting for a trend in the readout system, which tende o becomt d e more efficient with consecutive readouts of one dosimeter every 25 or 30 seconds over a period of several hou*".. { I 'no effect probably was due to a rise in the temperature of the rc.-.'j'-r electronic t sentirel no whic s wa h y compensatee phototh y b - r fo d r . i •". ior% cooliriu circuit.) The results of the survey are shown in .;;;>., ,•- onstratin • ." f. g tha r ovefo t0 percen8 r a tota f f o tabouo l 0 90 t ,r ' ..,r;.-yi"J ehe dose interpretation was within 5'percent of the requested >'.(, -, '7 '-, oy (30;! rad) to water.

t£ahJuiT^-p_o_si^eJ^ry_ Su_ry_ey j r,urvc. f high-energo / y bremsstrahlung dosimetry e cannoon , t rule oui LL 1Ü.c .u ; contributio o dosimetet n r respons f low-energo e y photons i:.igril, '.'dry sufficiently from e rrachinhighth f -o o machint ee us o mak t e th e atoniic-nuiiibcr GaF,,:Mn dosimeter undesirable. Gecausc of our experience in the past with spurious readings on LiF both in the form of powder and in the fori f TLD-10o u 0 chip e firsw s L tT investigatef o t ar e e statth th df eo dosiüietry with lithium borate, whic s commercialli h y available e eitheth n i r form of discs in which the crystalline powder is incorporated in a vitreous

81 material(Studsvik e for th f pressed-powde o mn i r )o r chips (Harshaw).e Th * results revealed e presentha th vien i tf o wt stat f developmeneo f lithiumo t - borate TLD materiae th , le recommende b coul t e planneno dth r dfo d survey. (The lithium-borate powder in the vitreous matrix fades more than the pressed lithium-borate chipsn contras i e presse t th ,bu o t d s chipi t i s t hygroscopic.**no e thereforW ) F i L ef o adviseo continu t e us H BR e d th e TLD-100 which they are employing for a number of other surveys, in conjunction wit a hot-nitrogeh n reader preliminara n I . - be ye studth f o y havior of 200 identically irradiated TLD-100 chips handled with suction picku d reproduciblan p C followey° annealehou0 1 40 hou1 y r b dt r ra fo d C befor° 0 a10 et irradiatio d anothe an nC befor ° minute0 0 1 r 10 e t a s readout, spurious readingt occurno d .di s This annealin d readouan g t procedur s repeateewa d nine times oveo weekscourse tw e th r Th f .o e results of the study indicate that there is about a 1.2-percent relative standard deviation from the average of the day-to-day readings on a single chip e relativTh . e standard deviation froe average th mth f o e readings of all the chips in the batch generally will be larger, its value dependin e e readingsprea e th th selecte n th n i o dgf o s d chips after identical exposure. For the present study, a batch of 100 chips was selecte d3 percen _ wit+ a h t sprea n readings i dy give an n nO .day , this batch yielde a d1.8-percen t relative standard deviation froe averagth m e e chips e th reading th l .al f o f o s So far, our investigations have included studies on the choice of phantom material and phantom size for source-to-axis-distance (SAD) irradiations with a 10 cm x 10 cm field size at the various depths of e possibilitinterestth n o d f obtainin,an o y g depth-dose information o n e participantsth ' a singlbea y b m e irradiatio a numbe f o nf dosimeter o r s positioned at different phantom depths, all on the beam axis. The results were: (a) Within the measurement uncertainty, the TLD readings -2 obtained ove ra rang f e depthphantoo e th m n c i s mg fro0 1 mo t abou 5 0. t

*Comtnercial product identification doet implno s a recommendatioy r o n endorsemen y NBStb r doe ,implt no i s y thaS considerNB t e identifieth s d products to be the best available for the purpose. **We subsequently learned that the increase in fading also will be observed e crystallinth n o e powder use y Harshab d wintroduces whei t i n a n i d vitreous matrix.

82 with cobalt-60 gamma radiation are nearly the same in phantom consisting of a polymethyl methacrylate (PMMA) cube with 15-cm sides and one with 20-cm sides. However, there is a trend toward higher reading e largeth n i sr phantom.* (b) Within the measurement uncertainty, the readings obtained ia PMMn A phantoe singlon n i me irradiation with dosimeter t deptha s s _2 e sam th s thosa e e ar e obtaine m c betwee g n separat i 0 d1 d n an aboue 5 0. t measurement t eaca s h depth. However a wate n i , r phanto whicn i me th h dosimeters are held in plastic inserts, there is a significant difference e readingith n f dosimetero s s irradiated separatel d simultaneouslyan y , probably because of displacement of water by the plastic inserts. We further obtained a cobalt-60 gamma-ray calibration of the TLD-100 samples in PMMA in terms of absorbed dose to water as a function of depth e phantomith n e distancTh . e betwee e detectoe sourcth th n d s kepean rwa t constant (1 in) and the beam cross section at this distance was 10 cm x 10 cm. e readingTh s obtained were compared with source-standardization data derived from absorbed-dose calorimetr e sam e th sam eth n i ey bea r fo m field size and distance. Figure 5 shows the results. The readings were arbitrarily fitted to the absorbed-dose curve at a depth of 5 cm, but could be fitted just as well at any other depth. Also, in order to tie in directly with IAEA measurements e sen,w r phanto ou t f 20-co m m side length, loaded in several depths with individually calibrated LiF-TLD-100 samples, o Massachusettt s General Hospital (MGH r irradiatio)fo n theii n r 10-MV bremsstrahlung beam unde e conditionth r s employe e cooperativth n i d e study with the Harvard School of Medicine and the IAEA. A preliminary evaluation of the results after return of the loaded phantom to NBS gave -a value of quotiene absorbee th th lulr f f° lo t d e dos th wateo t ed an r H quoteMG y b d cobalt-60 equivalent dose to water evaluated at NBS with the aid of absorbed- dose calorimetry data. This agrees well within the uncertainties of the measurement and evaluation with the value of 1.014 for this quotient, obtained in the MGH-IAEA experiment of March 1, 1979. (See table II on page 124 of these Proceedings.) For the NBS-MGH study, the relative standard deviation of

*This finding agrees with earlier depth-dose measurements witn chamberio h s in graphite phantoms made by J. Pruitt and S. Domen of our laboratory, who found a difference of 0.7 percent at a 10-cm depth. 83 a single reading froe averagth m f nino e e TLD-100 sample reading eacn i s h of four different phantom depths was about 0.7 percent. Finally, in order to arrive at the number of dosimeters required per measurement (correspondin e numbeth f o readingo t rg s froD powdeTL m r at any one measurement position) for a preselected level of uncertainty, we made a careful assessment of the random and systematic uncertainties entering into each step of the dose interpretation. The steps considered were: ) Cobalt-6(a 0 irradiatio n dosimeter f o n s (applicable also t o powder sufficien readingsn r e selectefo tth n )i d geometry readoutd ,an . ) Relatin(b n reading e average cobalt-6e th gth th o f t so e 0 gamma-ray exposur e pointth t .a e ) Irradiatio(c m f dosimeterseto nf o s varioun i s s calibrated high-energy bremsstrahlung beams of the type to be surveyed. (d) Relating the average of the m readings to absorbed dose e high-energo watet th n i r y bremsstrahlun e deptg th beaf interesto ht a m . ) Determinatio(e e correctioth f o n n e readingfactoth o t r s obtained with cobalt-60 gamma ray e irradiatesb f sample(steo i t ) e a p ar sd with high-energy bremsstrahlung instead (ste. c) p Preliminary resultr analysiou f o s s show that r suitabl,fo y selected batch-calibrated TLD-100 samples, averages from reading 9 sample n o s s n uncertaint a lea 4 percen finae o o t dth t ln 3 i t dosf o y e interpretation. When individually calibrated samples are used, this value is lower by abou e percenton t . t presentA e absorbe,th d dosr high-energfo e y bremsstrahluns i g usually determined froe respons th me bremsstrahlun th n i e gn a bea f o m ionization chamber originally calibrated in terms of exposure with cobalt-60 gamma radiation and multiplied by a suitable correction factor (C,).e Inasmucth e uncertaintf o th e s b a , which C, y n ma hi y percent5 o participantsl t ordeal 4 e sam,r f o th rwilfo e s e b lwa t i , decided to exclude it from the estimate. If, at a later date, calorimetric measurements will be used to obtain the absorbed dose for the high-energy bremsstrahlung irradiations e treatmenth ,e resultinth f o t g uncertainty will be reconsidered.

84 Acknowledgment wore kTh .relate o dosimetrdt n cobalt-6i y 0 teletherapy

beams discusse n thii d s pape supportes wa r e Radioactiv th n pari d y b t e

Materials wore Branchth kd relatean , o dosimetrdt n high-energi y y brems-

strahl ung beams by the Medical Physics Branch of the Bureau of Radiological

Health, FooDrud an dg Administration . DepartmenS . U , f Healtho t , Education

and Welfare.

References

1. M. Ehrlich, National and International Radiation Dose Comparisons, IAEA-PL-479/8 (1973). . 2 Protoco r Dosimetrfo l f High-Energo y y Electrons e Subcommitte,Th n o e Radiation Dosimetry of the Am. Assoc. of Physicists in Medicine, Phys. Med. and Biol. 11_, 505 (1966). 3. See, e.g., H. Fricke and F. J. Hart, Chemical Dosimetry, in Radiation Dosimetry . Attix H . . TochilinRoesc E C . F d . , ,W , an hVol2 . , editors, Academic Press (1966). Chesler. N . Gump. . HertS H S . . al.t ,B H . ze 4 , Trace Hydrocarbon Analysis, p. 49, Appendix A, HBS Technical Note 889, U.S. Government Printing Office, Washington, D.C. (1976). 5. K. Scharf and R. Lee, Rad. Res. 16, 115 (1962). 6. Catalog of NBS Standard Reference Materials, MBS Special Publication 260, , U.S.55 d Governmenan pp 2 . t Printing Office, Washington, D.C. (1975-76). 7. L. A. Machlen, Center for Analytical Chemistry, National Bureau of Standards, private communication. 8. M. Ehrlich and P. J. Lamperti, Phys. Med. Biol. H, 305 (1969). 9. A. C. Lucas, The Harshaw Chemical Company, Solon, Ohio, private communication. 10. B. E. Bjarngard, B. I. Rüden and B. waldeskog, Evaluation of Results a High-Energ r fo y X-Ra d Electron-Dosimetran y y Stud n thi(i ys Proceedings volume).

85 Fig 1 . Fricke Dosimeter Units e spectrophotometeTh . r cell fits snugly inte polystyrenth o e blocke finisheth n i ; d assembly a ,styro - foam plug presses agains e stopperth t d n placekeepi ,an t i s.

ijj'O I

œ ul g 50

PERCENT ERROR

Fig 2 . Electron Dosimetry Performance, 1967 throug hdosee 1975Th s. assigne 8 percen 5 e dosimeter th o t df to s agreeS dNB wite th h dose interpretatio withio t n percent5 n 3 percen;2 e th f to dosimeters showed differences between 5 percent and 10 percent, an9 percen1 d t differe y betweeb d percen 0 1 0 npercent4 d an t . 86 Fig. 3 Schematic Diagram of the CaF2:Mn Bulb Dosimeter (center) and Polystyrene Halveo th f Tw o s e th e Holder (lef right)d an t .

too

eo Ul I z (T 60 ï y

u. o cr ImUJ -Mi-

n „-..-,i <-25" -20 -10 0 10 20 ' >25 PERCENT ERROR

Fig4 .Performanc f Participanteo s Involve Surveye th n i d. Shows i n the difference, in percent, between the dose to be delivered by the participants and the NBS dose interpretation from the averagresponsee th five f th eo e f sirradiateo d dosimeters. 87 F u in 90

tr.LU a j ABSOHBED »osr.

LÜ in o f! O LU

I 1/5 6 10 Cti DEPTHm c ,

"icj. 5 ; 'Co CalibraLion of TLD-IOO in a Ib-cin x Ib-an x 15-CM Poly- i-ethyl ."ethdcryldte (PMMA) lhanto:.i. 10-c::i x lO-cm field si/e

aL each depth. Solid lino: j absorbed dose to water; error bars: standard déviation (••- O./ ) for a single dosimeter readimj obtained fronaveratje th : o readin calibrate9 f o g d dosimeters at each depth. The average dosimeter data were M tied to the dhsorbed-dose curve at tic arrow (at a depth of 5.00 cm in P/'-'A, corrosuondincj ;.o :>.'// q cnr in wa'cer, deptc whic Lh n walei h s r i hwhic fo r e percenth h t depth dose ? s approximateli t e !>.0a n sd:;:ti PMMA) th yn s a 0;Ci .

88 REVIERESULTA E TH F WO S OBTAINEY DB NPL/PTE TH B FRICKE DOSEMETER CALIBRATION SERVICE IN GERMAN RADIOLOGICAL CENTRES

H. FEIST Physikalisch-Technische Bundesanstalt, Braunschweig, Federal Republi Germanf co y

In 1972 the Physikalisch-Technische Rundesanstalt (PTB), the national standardizing laboratory in the Federal Republic of Germany, decided to make the Fricke Dosemeter Calibration Service of the British National Physical Labora- tory (NPL) available to German radiological centres. This service has been establishe y Ellib d n 196i s 9 (1) e iraiTh .n feature f thio s s postal reference servics followsa e ar e : Fricke solutio sealen i n d pharmaceutical plass ampoules is made available by the NPL twice per year in May and November. The PTB dis- tributes the dosemeters to the participating institutions, collects them after e irradiationsth r evaluation fo d return an L , NP e s th theA .wate o t m r phantom and data sheet o protocot s l detaile irradiatioth f o s n condition e providear s d by the PTB. Moreover, the PTB offers general advice and assistance in analyz- ing the results. Apparently this activity is very similar to the manner in which inter-comparison IAEAe th e carrie.y b ar sEac t hou d participan dosemetea f to r issue can obtain a set of 10, 12 or 14 ampoules, 4 of which have to be left unirradiated as controls. Of course exceptions are possible and higher numbers of ampoules are conceded when an extensive calibration program is taking place y centerian n e perio.Th f timo d e that elapses between dispatchin e doseth g - e evaluatioth d meter averagen week5 an a s L n i nsso NP froe . th m

The dosemeters are offered for irradiations in the water phantom with cobalt-60, high energy electron MeV)8 > ( megavoltagsd ,an e photons partie .Th - cipant e aske sar o irradiat t d t depthea appld an s y conversion factors given by the corresponding ICRU Reports 14, 21 and 23. In order to secure identical irradiation condition eacn i s h institution phantome th , e suppliee ar s th y b d PTB e user eithereny wateo Th e . rma tth y rbu phantom watee Th . r containers themselve e ordinarar s y polystyrene fish tanks (Fig whic) 1 .e kep ar n hi t stock .A suitabl e lid e chemica ,holdea th r fo rl dosemeter d fitte,an d holders for the ionization chambers, according to specifications given by the user, are manufacture B workshopPT e th n .i d

With cobalt source e irradiationsth Fricke th f eo s dosemeter e doseth d - san metercalibratee b o t s e usuallar d y performed sequentiall beae th m n yo axi s e phantomith n r irradiation.Fo s with accelerator recommendes i t i s o irrat d - diate both dosemeters simultaneousl botn o y h beae sideth mo t f saxi o d san swop them several times during the irradiation in order to overcome beam in- stabilities.

89 Each dosemeter SLiOJU obtai n absorbea n r thidFo sdos . f aboucasGy o e e0 4 t a random uncertaint r cobal f aboufo o y L ttNP irradiate+0. e quotes i th 5 % y b d d % confidenc 5 9 ampoule e th et a sleve l wit degree8 h freedomf so determino .T e this uncertainty f ampouleo e samt th se e f a so batc, s irradiatei h d with cobalt in the NPL at about the same time as the irradiations take place in the centers. These ampoules are evaluated together with the returned dosemeters of the participants. Since 1977, further independent cobalt irradiations have been carried out in the PTB in order to rule out "travel effects". The differences resulting from the absorbed dose determinations by the PTB and the NPL have always been les. s% tha5 0. n

(Afte a pilor t stud n Novembei y r 197 e regula2th r Fricke dosemeter service r Germafo n hospital d othean s r interested irradiation centres startey Ma n i d 1973 e tabl.Th e illustrate e developmensth t till now.

Table. Number of participating centres and of dosemeters irradiated in Germany between 1973 and 1978.

Number Dosemeters irradiated with Dat f issuo e e f centreo s Co electrons photons

May 1973 9 41 19 10 November 1973 6 7 33 11 May 1974 9 25 40 16 November 1974 4 7 18 8 May 1975 7 23 21 13 November 1975 8 25 28 24 May 1976 7 25 26 10 November 1976 11 35 23 34 May 1977 7 26 27 12 November 1977 11 31 31 8 May 1978 9 25 27 18 November 1978 9 28 31 20 Total 97* 298 324 184

0 differen4 * t centres. Som f theo e m took part several times.

Fig show2 . s frequency distribution ratie th f absorbe o f o s d dose determined by the user to absorbed dose measured by means of the Fricke dosemeter r cobalfo s, electrons60 t megavoltagd ,an e photons. Additional- e frequenclth y y distributio e cobalth f o nt irradiated dosemeters (left side below) is split into two fractions- Intercomparisons made during the first period froy 197y 197Ma Ma m 63o t (left side above d thos)an e during tne second, period from November 19?6 to November 1978 (left side middle). e mosTh t striking featur f theso e e distribution e asymétrith s si e shape. Wherea e asymetrth s onls i y y slightly indicated durin e initiath g - pe l s morriodi et i ,marke d durin e lateth g r one explainee .b Thiy ma s s a d follows: In the beginning the users could not refer to reliable calibration factor f theiso r lomzation dosemeters. Henc distributioe th e s i n wide-spread. Later on some users adopted the calibration factor obtained

90 from a previous participation in the Fricke calibration service. Other institutions used calibration factors obtained froe manufacturerth m , the Physikalisch-Technische Werkstätten Freiburg (PTW). There are, however, some indications thae calibratioth t n factors that originate from this laboratory tend to be lower by 1.5 % than those originating from the NPL. The difference may eventually be due to the primary standardizing laboratory which is the PTB. Therefore the PTE is going now to investigate this phenomenon carefully.

The fact that it is possible to resolve such small effects, proves e precisioth n claime r measurementfo d s with Fricke dosemeters. This i s n essentiaa l advantag e Frickth f eo dosimetry, which shoul e takeb d n into consideration for intercomparisons, when a total uncertainty of less than 2 % is required.

The results of the electron irradiaticns are poorer. Several facts increas uncertainte th e f electroo y n interconparisons r instancefo , : a) Strong dependence of the absorbed dose conversion factors or. the electron e effectivenergth t a y e poin f measuremeno t t whic usualls i h y differen e ionizatioth r fo t n e chambeFrickth d ean r dosen:eter. Unknow) b n contaminatio e primarth f o ny electron bea y photonb ~ r strao s y electrons.

Furthermore one has to rc.i'.ize that rrost of zni chsnbers have not been designed for electron irradiations and nught have suffered from a "pola- rity effect" (2) t shoul.I d als mentionee b o d thanese th tt significant discrepancies occured whee electroth n n energ s belo e recommendewa y th w d lower ]im:t of 8 "eV. Allowing for all these sources of uncertainty, the results are quite satisfying.

Similar considerations are valid for the megavoltage photon irradiations. Of course the- asymétrie structure of the cobalt distribution is also reflecte e electroth y d photob d an n n distributions since many institutions carrie ; intercomparisonou d s usin e samth g e calibrated ionization chamber for HJ 1 three types of radiation.

Finally two outstanding results of this caiinration service are to be mentioned. The first result is that a discrepancy between absorbed dose determinations based on the C^ concept and on the measurements with Fricke solution respectivel V bremsstrahluns beerMe ha y ,2 & foun r fo d g already in 1973 (3). On an average, the absorbed dose determinations by means of Fricke solution usually give values that are about 3 % higher than the results of ionization chamber measurements for this radiation quality. This might arise fro a trum eabsorbee valuth f o e d dose conversion factor tha s highei t r thae valuth n e recommende e ICRUth n I y .b d 1974, a discussion on the discrepancy between the C and the C^ concept was launched, mainly by Greening (4). Now it is commonly agreed that the compositio e ionizatioth f o n n chamber wall affect conversioe th s n factor

91 and increase bren'Tt.rohe V recoir-endeth "r s 2 £- r fo 1.unp, c' " vajvi, y : e if iiri ior.izaLion chnr-jtsrr •*!•„;, a*, r '.:•;•; i v« .or:' *alls> :s •,.£•.>.;:! !L>;. Tp.vrs.Ti- j:atior.B c't. the ï'Tiî ccnf :.ri; ed î.ht-i'.e f .:r)!i:::p:: •: '.

The second cutslar.dir'.p rt-oi—:. .U; cr. c VI-KT. .n <.'. ^uri'.r::. university hcs- pjt,ai , happeneI' . d st/on aftrr Ir.o o>:c':.Er.~( t sourcerr : ; cobal ' i Ji c* - 1 t uni'^. In s-.pitc of h recul '. : rf-ti or. c:" thr :cr.'. ;'.rjv:io:-. dor,e:.-eter nei'ore the exchange procedur d -:•.an e s»pit f rt'ful^o e r cr.t.ck; f tric - e dore rn'oec tn , r.Cc.K'jre:nrr.-s h t Frick; *• : t cofic.Tic'.or ' ' , clc\-o

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:. I c--( '. y ff::.firre- d thr rcr-,;l;:; oo^oi:.« ri iv T.'-.o .'r:::K(! co".rn( *,.prs;. IL har, e r.-I.rb o :t i l.' tr.<-ie «r ,W:.Gh r t > affr.i r r..t.i":^ r I :-;i:.rT r rv.-s: erio;:£,. Any a y* 'vi.c1 Fricke col it/ration srrv. ce i.a£> vrever-tcd that ss^riojs; hc.rr1 A'JIS cajnec. '"iir ".otnor /-ratof i.Py ackr:oA'lrd,~t .•; r-r\:. v Ji:rf..'. r:i :•"'.:<• F:oriî: v::h "T. F. C. KJlis of the N;-i: ioîiFil rjysicc'.i L,;"j(.'i ûL": y 'i < i:<:. r.f.icin.

~~i'ri' er on fee:~~

(1) rljis, F>.C., 7r. ;:;;•;L rc - Ir.fil.icr f o Jjiisor'ije. d dos,o star.darri y chrii.icsb s i dosimetry nec::;ir K-I.i . i-.:-.c c /,-.. ^h jse. iv.f -o i ::cBC-ioter, Ion: /.inj', Radi;:- tion Xetroloci'i eti: '.' i; ;:y i: . Car.,",:1..! (197"! (2) Markus , lor.Ü. , i z;-,:, lor. cr.".-i."< ri >, fret f c polarit- y {.fie , rta intende d for electron dccir.ctry , IAEA-S"-"n')" '3'-

(3) y'o-.Rt. , ErfeL-r.'H. , . s f.;r>cDouco : a noTor-Vrrfli'ic'.'.i-dierictt's; cier J'T3 ;:r- .t tols cnerinohcr "or- ;,,;:: : i •..>:-, Mod inir-ch. :/ o F:.yr,: n Fcrachunfi k d un , Praxis, edited oy A. Kiiui 'I3'76; (^) Grecnint; , DOP. i : P . J converaic:, . fictcr. r electron:;fo s , Phys. Heo. 3 G (1974) 7/.6 (5) /• J-Tor.c: , F. 1?., Sverinr.cri , :-;., loniî'.fi! ior. c:.r. :.'•:.<.• r nosiiie'ry for phoron and electron bear u , Acta had:o:. Vnc.r. rhys. ;;-Ol. J^C >: (1Ü77) 177 i > (6) Feist, !!., Urr>.t ru'.:c. :.:r.f) des Konvcrn:or.r.f;:k'cort. >:ur P(:s~.:"..uri£> der F.nerp.i t'dosîis in 'J.a:;scr f'.:r !!r(;r::a Lr;.::lurip vor. ^-? "cV C.-rc'nzenc'rf ie , Vedizir.ischie . i'hysiü r- , eic D 7 kh l-.rr.p., iiUth;;- Vcrln;- Koidnibcrp, j.r Druck.

~~92 !Ul uM iUl~~

~~214~~

~~eCDn~~

~~230~~

~~polystyrene Sketc. Figl th . f ho e water phantom with holdechemia r rfo - cal dosemeter.~~

93 020- 60rCo (May!973-Moy!97GI 0 15- (130) 0 10- electrons 0 05- 0 20- (May 1973-Nov 1978) (316) 0- i ,,M,l | i | |I l 1 || , . Il 015. 10 025- 0 10- 50Co 020- (Nov 1976 -Hov 19781 ° °5" 015- 1136) o- /^H[- ^al - Il Ml h M -u 080 B11 092 5 0910 5 0 1. 010-

~~005- 1 r I 1 : o-i lit. ,1 I i f ,,,,,, megavollage photons 10 ; 025- 020- (Hay 1973-Nov 19781(187) \ 020- Co total fl]sj (Hay1973-Nov 19781 015- (266) 010-~~

~~010- 005- 1 1 1 1 0- i 005- -4J-1- v1—f- — n r l h - - • . 083 092 095 10 105 110 n- |.| l i , I.. 1 1 1 i . , t , 0 1 l 5 10~~

Fig. 2. Frequency distributions of the ratio R of absorbed dose determined by institutions to absorbed dose measured by NPL Fricke dosemeters for various radiation qualities. In brackets time period and number of ampoules.

~~94 FeSOF SOMO N THI E EUS PRACTICAL ASPECTF SO~~

~~HIGH-ENERG4 Y PHOTO ELECTROD NAN N DOSIMETRY A. WAMBERSIE, M. PRIGNOT, Cliniques universitaires St-Luc (U.C.L.), Bruxelles, Belgique A. DUTREIX Institut Gustave-Roussy, Villejuif, France~~

Abstract f FeSOo n e somi ,us e e practicaTh l aspect f high-energo s y photon and electron dosimetry. e advantageTh f FeSOo s e discussear , d with respecs it o t t applications in practical high-energy photon and electron dosimetry: (1) the calibration oE ionization chambers, (2) the evaluation of the importanc n recombinatioio f o e n chamberi n s expose o higt d h dose e determinatioratesth ) (3 , f absorbeo n d dos n radiobiologicai e l samples 'and (4) the use of FeSO, as a transfer dosetneter. The absorbed dose conversion factors, C or C\ of an ionization chambee determineb n ca r y comparisob d n with FeSO,.The response e FeSoth fO dos e G-valuee th mete a r functio e (o beas ra ) th m f o n 4 quality can be considered as constant for high-energy photons and electrons in the usual energy range.An FeSO, dose meter can also be use o evaluatt d e importancth e n recombinatioio f o e a chambe n i n r expose o higt d h dose-rate f electronso s , sinc s responsit e s i e independen. ) 0 Gy.1 s x f dose-rat2 o t o t p (u e Examples are given to illustrate the interest of FeSO^ for measurement f absorbeo s d dos n biologicai e l samples, mainl n depti y h in electron beams wher e dosth e e gradien s high.FeSOi t e b n ca , assume e insensitivb o t d o energt e y variatio o dose t n dept i nr -(o h rate variation); it does not introduce any heterogeneity and no dis- placemen e applieb t o factot s dfinally; ha r e dosth , e meter solution n occupca a volumy e identica e biologica th o that lf o t l systemo t s e irradiated.Fob r these applications e resultth , s obtained with FeSO are compared with those obtained with other dosimetric systems. r experiencOu e with FeSO, a transfeuse s a d r dosemete r interfo r - comparisons between center s reportedi s .

~~INTRODUCTION~~

Although ionization chambere dosemeterth e ar s s most commonly used for high-energy photon and electron dosimetry, the FeSO, chemical dose mete s propertieha r s which mak t particularli e y suitabl r severafo e l applications.The purpos f thio e s o papet s i r repor e maith tn r experiencpointou f o s e wite Frickth h e dosemeter in practical dosimetry of high-energy photon and electron beams.

95 The main advantages of the FeSO, dose meter can be summarized s followa s (Ref 1 ,2,3). : A hig ) h(1 degre f reproducibi1ito e y (l%).Foe applicationth l al r s considered in this paper we shall rely only upon the reproducibility of the FeSO,, and not upon its accuracy. r negligible(o o N ) (2 ) variatio e "responseth f e FeSOo nth f ,o " dose meter (optical density/ unit of absorbed dose or G-value) a functio e s radiatioa th f o n n qualite rangth f higho n ei y - energy electron o d abouphotont an 0 MeV p 4 - u ts - s. e respons Th e FeSO th ) .f (3 o e dose mete r G-value(o r s independeni ) t Ï — 6 of .the dose-rate up to 2 x 10 Gy. s (4) No ( or negligible) heterogeneity is introduced by the detector s containerit (an de irradiate th n i ) d medium.A a consequences , under usual conditions, there is no (or negligible) modification of the electron flux introduced by the detector. e dosTh e ) mete(5 r solutio e irradiateb n ca n n thii d n layers w millimetersfe a ( r radiobiologicafo , or ) l experimentse th , FeSO, solution can occupy different volumes and, in particular, volumes identica o thost l e occupie e biologicath y b d l systems to be irradiated.

e disadvantageTh e FeSOth f , o sdos e mete e alsar ro well known. Thee mainlyar y : w radiosensitivitLo ) (1 ) t leasGy a 0 r 5 t (o : dose yy G f abou o s0 10 t e needear r precisfo d e measurements; (2) The FeSO, solution has to be prepared and handled very carefully and kept in perfectly clean containers.

~~Taking into account these general properties of FeSO,, its interes n practicai t l dosimetr f high-energo y y photon d electronan s s wil e considereb l d with respec o fout t r application: s~~

e calibratioTh ) (1 f ionizatioo n n chambers; e evaluatioTh e ) importancth (2 n f recombinatioo nio f o e n i n ionization chambers expose o higt d h dose-rate f electronso s ; (3) The use of FeSO, for determination of absorbed dose in radiobiological samples; f FeSOa o transfe s e a ,us e r Th dosemeter ) (4 .

~~1.CALIBRATIO F IONI2ATIOO N N CHAMBER R HIGH-ENERGFO S Y PHOTONS~~

~~D ELECTRON——————————————————————————————————AN Y COMPARISOB S N WITH FeSO. 4~~

e measurinTh g instrument commonly a locause s a dl standarn i d a radiotherapy departmen s stili t n ionizatioa l n chamber.Foo C r (or 2 MV x-rays), calibration of an ionization dose meter can be obtained r checkefroo - - standarm y b d d laboratorie n termi s f exposuro s e

96 (röntgen) or absorbed dose (gray). In France,such facilities exist at the L.M.R.I. (Laboratoire de Mesure des Rayonnements Ionisants) at Saclay (Réf.4 ). However r high-energfo , y photon d electronsan s , calibration t easilfacilitieye t yno available.Fo e ar s r these conditions, direct comparison wite FeSOth h , dosemeter provide n acceptabla s e solution for calibration of the reference chamber in a radiotherapy department.Thi s beee methoha sth n r dCente ou user man n fo i rdy years (Ref.5,6). e chambeth s s beeA ha r n calibrate, calibratioCo r fo r d fo n high-energy photons and electrons is obtained by comparing, in Co,

photon and electron beams, the readings of the chamber and of the FeSO, dosemeter.We have checked that the FeSO. dosemeter does 4 4 not introduc y heterogeneitean e assumw d an ey thas responsit t s i e independent of beam quality (Ref 2,7). This beeha s n measured recentl n veri y y careful setf o s experiments carriey COTTENb t ou d S (Ref.3 r electrofo ) n energies rangin o g14.t fro5 5 3. MeV.m A G-valu f 1.60o e 0.030 _ 1 + 4 . 5 mol -kg . Gy was found for 7 to 14.5 MeV electrons and a G-value of 1.597. 10 mol.kg . Gy for 3.5 MeV electrons.Moreover a survey e G-valueth f o s obtained from calorimetric measurement s beeha s n published by SVENSSON and BRAHME (Ref.8).This survey indicated that the difference between the G-values could be partly related to inaccuracie e determination n i s a mea d n an sG-valu f 1.60o e 0.017_ 7+ , 10 mol.kg .Gy was calculated. s alreadA y mentione e FeSOus e , w d onl r relativfo y e measurements e applicationth n i s considere n thii d s paper. FeSO n easilca . e b y calibrated by measuring its "response" (optical density, 25°C,304my) to given doses of gamma-rays.Absolute calibration of each part of the Fricke dosemeter system (spectrophometer, solution) would normally require long and difficult experiments. Calibration obtained with this method is valid even if the beam energy is not known with great accuracy. Whe n ionizatioa n n chamber dose mete s exposei r o t d high-energy electrons e absorbeth , d a watedos n i er phantom e expresseb e y formulth ma y b da (Ref.2)

Dw=M.Nc.CE (1) where : = absorbe D d poine dose(in wate th i f measuremen o tt ) a r Gy n t whee chambeth n r syste s replacei m y waterb d . = instrumen M t reading correcte r temperaturefo d , pressure and humidity.

~~= exposur C N e calibration e chambefactoth f o rr dosemeter for Co garama-rays.~~

97 C - overall conversion factor to absorbed dose in water. C„b includes: a correctio- n facto r attenuatiofo r f photone o n th n i s chambe o radiatioC r walr fo ln during exposure calibration which is assumed to be 0.985 (Ref. 9); - the ratio of mass stopping powers for water and air, which is valid for the mean energy of the primary electrons at the point of measurement; - the perturbation correction factor. C values have been recommended r differen(Reffo ) .2 t E initial electron energies and different depths in water. Similary r high-energfo , y photons n particulai d an , r for the reference radiation quality ( Co), the absorbed dose e poinath tf measuremen o t a wate n i tr phantoe expresseb y ma m d by (Ref.!)

~~DW = where : D , M and N have the same meaning as in Eq. (1) C. = overall coconversatioi n factor to absorbed dose in water (in Gy/R). The recommended value of C, for Co is 0.95 (Ref,1)~~

Measured C values for a Nuclear Enterprises chamber are lj presented in Table I and compared with the C values recommended y ICRb U (Réf.2 d derivean ) d froe calculateth m d dat f BERGEo a R and SELTZER (Réf.10 d KESSARIan ) S (Réf.11).The irradiation technique e chemica th s wela ss a l l methods have already been published (Ref.6 ,12) A clos. e agreemen e s reachei tth r fo d conditions which have been studied: electron beams from 10 to 33 MeV (incident energy) produce y threb d e different type f generatorso s . e statisticaTh l e measurementerrorth n i s s (confidence leve f 95%o l ) are indicated in the Table.A set of six Nuclear Enterprises chambers 3 of the same type (vol. = 0.6 cm , diam.=6 mm) were compared. Although the N factors for Co were different (1.01,1.04,1.05, 1.06 and 1.08), the observed C value$ as a function of electron energy were the same for all the chambers, within the limits of reproducibility of the measurements.

~~EVALUATIOI I E IMPORTANCTH F N RECOMBINATIOO NIO F O E N IN IONIZATION CHAMBERS EXPOSE O HIGT D H DOSE-RATES~~

With the higher dose-rates actually available with modern electron beam generators, ion recombination needs te be taken into account for the usual ionization chambers.The main reaso s thae i dealn on t s with pulsed radiation; moreover, when a n electron bea s "scannedi m " ovee irradiatioth r n field e ratith , o is still higher betwee e "instantaneousth n " dose-rate th r (o e dose per pulse) and the "average" dose-rate(which is measured).

98 Correction factors for ion recombination can reach several per cent n treatmeni s t conditions d evean , n more durin» calibration procedures or biological irradiat ions.(We only consider hero conditions clos o thost e e encountere lit e t n therapyi no d o d P W , consider t lie "ver y high dose-rates" which can be obtained with r accelerators)a « n i l l a i tp »c s . e dose-raten Tabli th d , I e e nl e s e date s th r p usear F o d were low, so thai corrections for ion recombination in the chamber wore smal r coulo l e eenegb t A d maximu l . . lec o mt correctio d ha X I f o n applied (Ref .-Correc) .6 n n factorrecombinatioo ti io r fo s a n i n chambee determineb n ca r d theoreticall r experinontaly.Io y a n first sot of experiments, the correction factors were determined i'rom the variation of the dose meter reading associated with a variatio e voltagth f o n e appliee chambeth o t d r (DUJ'REId an . A X COHKN L . , unpublished dat a , 1 9 7 5 ) . The results were, in a good agreement wite theoreticath h l calculations derived froe th m formula propose y BOAb d (Kef.13G• • ). T.a f seconexperimentsno t se d e readingth , a commercial f o s - ly available Nuclear Enterprises chamber were compared with the. respons e KeSOth ,f o edos e meter,sinc s assumei t i e d thae resth t - ponse, of the latter is dose-rate independent up to 2 x 10 Cy.s"' (Ref.2). These measurements were performed wite Sagittairth h e linear accelerato e Instituth f o r t Gustave-Roussy.In this accelerator 100 pulses of 3-ys duration are emitted per second, and the irradiated field is "scanned" by the. electron bcani with a frequency Kecaus. e scanninth s f o e6 og0. f system e ratith , o betweee th n average dose-rate and the instantaneous dose-rate is complex and depends on electron energy, as the size of -the primary pencil beam varies with electron energy. r resultOu e presentear s n Tabli d whicT I e h shows that correction factors derived from comparison withn i FeSO e ar , »ood agreement with those obtaine e ionisatioth y variaf b do n iio n chamber vol tage . Figure 1 compares our experimental C,. values taken fro I witmT Tablea htheoreticad an I s l curve derived f Uof.2o 7 3. . frog Fi m A systematic study of recombination has been performed more recentl s wor s i ha Th ky MARINELT. b . y ) 4 1 . d Collf an e O (R . shown for example that in a 30 MeV electron beam produced by a linear accelerator Sagittaire, the ion recombination in a Nuclear Enterprises chambea mea t a s nabou wa , rdos 77 te rate of 1.7 Gy bu-t reached 16% at a mean dose rate of '3.8 Gy.

,9,9' E FeSOTH F .O DOSEMETEE US l R DETERMINATIO——————————————————4————————-———————————————————————————Il FO R F ABSORBEO N D — DOSE l'.î BIOLOGICAL SAMPLES

e previouTh s paragraphs dealt with absorbed dose measurements at the level of the maximum of the depth/dose curve, wher e depth/dosth e e curv s relativeli e y flat ("plateau region") .Déterminâ f absorbeo n tio d dos n depti e h raises several problems.Accurate depth/dose determinations are needed for studies of RBE as a function of electron spectrum in depth in a high-energy electron beam (Ref. 12). Firs f allo t e respons,th n ionizatioa f o e n chamber (esu/Gy) varies with depth since electron energy decreases. a consequenc s A a correctioe n relate o electrot d n energy e applied.Thib o t s ha s assumes thae electroth t n energy at the point of interest in known with accuracy., e seconTh d problem concern e poin th sf measuremen o t t e ionizatioth f o n chamber.On n admica e t n thatelectroa n i , n beam e poine referreb th , o whico t tt e dos th s hi d e lies betwee e anterioth n e e chambecenterth th walf d o rr an l o thas e uncertaintth t y abou s positio it t mostta , ,is n equal to the radius of the chamber.Us ing cylindrical chambers of various diameters (Fi, irradiate2) g d perpendicularl o theit y r axiSjDUTREIX and DUTREIX (Ref.15) found that in a 20-MeV electron beae pointh mf measuremen o t t liee n fronth i s f o t e radius.Howeverth centef o a distanc 3 t a r2/ f o e , this distance may vary with the electron energy, the depth and the typ f chambeo e r (diamete f r centracavito ai d f an o yrl electrode etc.).HETTINGE . (Ref.18al t e R )e th foun f o a distancd 4 3/ f o e radiu e centen fronth i s n f electroi o rt n beams produced'ia n 35-MeV Brown Boveri betatron. Whee dos th s nrathei e r unifore "plateath n i m u region" f littlo thi s i s e importance t whe e dosbu , th n e gradiens i t high thin introducca s e considerable errors.For example, at the 30% isodose level in a 20-MeV electron beam, a change m correspond n dept1m i f o he a changth o n t si f abou o e% 10 t absorbed dose.

~~A FeSO, dosemeter doet presenno s t such disadvantages:~~

~~(1) It can be assumed to be insensitive to energy variation in dept r dose-rat(o h e variation) t doeI t introduc no s) (2 y heterogeneitan e o displacemenn d an y t e appliedb o factot s ;ha r~~

100 (3) The dosemeter solution can be used in thin layers (a few mm) n occupca r a o volumy e identica e biologica th o tha t lf o t l system o irradiateb o t s d (for example suspension f bacteriao s , yeast, etc.) in order to avoid any "geometrical" error (see Figs 3,4,5 and 6).

However, a practical problem arises when the dosemeter solution is used in thin layers, for example in Perspex cells: s importanii t o avoit t d chemical reactions wite wallth hf o s s.Therl l thee e e fore cellth e s mus e cleaneb t d very carefulld an y must be pre-irradiated at a high dose (a 1000 Gy).Ac cording r experiencetou o a ,reproducibilit f betteo ye b n r ca tha % 1 n achieved with these precautions (Ref.12).

~~F FeSOO A TRANSFE E S A ,US E RITH V DOSIMETER.~~

e mosth tf o interestin e On g application e Frickth f eo s dosemete s usea transfeit s . a s i r r dosimete r comparisonfo r s between different radiotherapy centres.The advantage f suco s h comparisons in maintaining consistency are generally recognised and it is for this type of application that IAF.A is indeed mainly interested in the FeSO,. r experiencou s a r fa e s witA h intercomparison s concernedi s , e performew n 197i d 3 (Ref.21 a compariso) e dosimeteth f o n r calibration for Co. Twenty centres ( from France, Belgium and Switzerland) too e kstudy.Eac th par o t t h centre receive 6 FeSOd , samples to irradiate at doses ranging from 70 to 150 Gy.The mean of the standard errors observed for each centre was about 0.57 which indicate e higth s h leve f reproducibio e lmethod th f o .y t li This reproducibilit t leasa s tr bette wa yo equa , to rl than, that achieved by other groups with FeSO, or with other techniques (Ref.22 , 23 ) . As already reported in detail, 2/3 of the centres were withi % fro2 e mean.Thre_ + th nm e d centrean % 5 so t diffe 3 y b r five centers differ by more than 5%.Our solution samples have not been mailed, but have been distributed taking opportunity of meeting r travelo s f somo s e membere differenth f o s t centres. a secon n I d serie f experimento s s (Ref,24), FeSOs wa . use o compart d r dosimetrou e y with Edinburgh.Furthermore,as the two centres were using FeSO,, this opportunity was taken to compare the responses of the solutions and the spec trophoto- meter (value of c) . The observed agreement was better than 1% for each compared parameter: absorbed dose, e, and G.

~~101 CONÇU i ON :s .~~

Tu conclusion, I' lie I'd SO, close1 i:>ot. or has certainly boon l.ho only available-: 1:10. Clio <1 for h i ;>, h-o. no r j;y photon ;!ii(l electron dosi- d no . i H o Un a r t foie ) c öl K1 1 y : checkinu ap s r o r o ( o ch • n li ROtr r e th n gi y s L n n o chamber; o i i ' : i ; (. ; i a . v timf . i f r a 1 o ;e0: o : : vit: c i.o. 1 uhe:n ; a r b ii l .h-ene . 'P (for .r ;» y electro d photoan n n beamsy an ) error arisHng fron an inaccurate, evaluation oC beam energy of the si>ej!:run is avoided. The same remark applies when recombinations in i o n i •/. a t ion c h a PI b e r s a re b p c o m i n f, i m p o r f. ;-i n l. . When an ?eSO, dostür.e t e r is no_t _ ava_i_labl_£ in a laboratory o a;>rew (and e that »real: s (-ari needee d with t'eSO^ o t obtai, n

reproducible moa suroT.en t s) , l.''eSO/ can be used as a "transfer" dose •noter and p r e p a r e d a n d re a d by n a t ion a l a n c! i n 1: e r n a C i o n a l I a b orator i e s . i-'injilly, in hi. gii-ener gy electron r a d i o b i o l o K y , KeSO^ is probabl e mosth y te absorben suitabli m r er . t systec e di d er t cioo e t mm si . i no s t s y s 1 a c i g o l o i b n d i oso.

~~S K C l-R N E K E R~~

) tI.CIU(1 i .h w ;s Repory , ra : Radiatiomi( a X-ray - Ç y r e n.' a .r l ni td i an s o D n Maximum Photon Energies between 0.6 ai:cl ">() Me.V, International Commission on Radiation Units and Measurements, Washington, i). (1969) .C . (2) ICKU Report 21, Radiation Dosimetry: Electrons with Initial Energies, 15c.twe.en 1 and 50 Me V , ! n te rna t i onal Commission or; Radial: ion Units and Measuromen !: s , Washington, D.O.(1972). (3) COTTMNS , F.. : Ueabsorbeo rc.l e dosis k al or inie t r i c by hoge énergie e 1 ok tronenbunde 1 a en onder i-.oek van de L j zer sul f aat dosimeter Cent 1979. (-'i ) (Hi 1 HO , J . P . , Structure de 1 ;: rr:é 11 c 1 og i.e en Franc.e, Laboratoire de Metrologie des Rayonnements Ionisants, C.K.A . -C.M . N./Sac 1ay , (1974) (r)) IMJTKF. IX, J., UKTRRIX, A., WAMBKRSIL1., A., Etalons secondaires en dos imctric , .T.Belge. Radiol./ij) (1966) 157. ) KAMBiCRSlïï(6 , DUTREIXA. , , VR1GNOÏA. , , DUTREIXM. , , Calibratio . J , n of an ionisation chamber by comparison with FeSO, for 'nigh en?rgv electron beam:; t.u i.ophS 6 ,R (19712 d. . 7 ys 16 )

102 (7) ELLIS, S.C., "The dissemination of absorbed dose standards by chemical dosimetry - mechanism and use of the Fricke dosemeter", in Proc. International Cours n Ionizino e g Radiation Metrology, Villa Monastera, Varenna, Lake Gomo, Italy 3 Sept 1972 , Oc -4 (National Physical Laboratory, Teddington, Great Britain, Rep.Radiât.Sei.30, Dec.1974). (8) SVENSSON, H., BRAHME, A.: Réévaluation of ferrous sulphate dosimetr r electrons.Internationafo y l Symposiu n Nationao m d an l International Standardization of Radiation Dosimetry.Atlanta, c 1977De 9 USA.5- . (9) SVENSSO^, H., PETTERSON, S.,Absorbed dose calibration of thimble chambers with high energy electrons at different phantom depth, Arkiv Fysi ^ (19673 k 7 37 ) (10) BERGER,M.J., SELTZER, S.M.,Quality of radiation in a water medium irradiated with high energy electro n Booi n 7 beamsk 12 . p , of Abstracts, 12th Int. Congr.Radiology, Tokyo, 1969. (11) KESSARIS, N.D., Absorbed dosd cavitan e y ionizatio r highfo n - energy electron beams, Radiât.Res. 4_3 (1970) 288. (12) WAMBERSIE , ContributioA. , à l'étudn e l'efficacitd e é biologique relative des faisceaux de photons et d'électrons de 20 MeV du betatron, J.Belge Radiol.,Monographi l (1967)n° e .

(13) BOAG, J.W., Ionization Chamber Radiatio' 4, h C , n Dosimetry (HINE, G.J., BROWNELL, G.L.,Eds) Academic Press w YorNe , k (1956) 153. (14) MARINELLO, G., DUTREIX, A., CHAPUIS, G.: Etude de l'efficacité de collection des chambres d'ionisation cylindriques irradiées dans faisceaule s e rayonnemend x t puisé d'un accélérateur linéaire,J.Radiol. Electrol. 1976, 55, 789-800. (15) DUTREIX , DUTREIXJ. , , EtudA. , e comparée d'une série d e chambres d'ionisation dans les faisceaux d'électrons de 0 MeV,Biophysi1 t e 0 2 (1966_ _3 k ) 249. (16) HARDER, D., "Energiespektron schneller Elektronen in verschiedenen Tiefen", in Symp.High-Energy Electrons, Montreux, 1964 (ZUPPINGER , PORETTI,A. , EdsG. , ) Springer Verlag, Berlin, Heidelberg w YorNe , k (1965. 26 ) (17) WAMBERSIE , DUTREIXA. , , PRIGNOTA. , : ExpériencM. , e f FeSOo n e somi ,us ee practicath n i l aspect f higho s - energy electron dosimetry n Proc.Symp.Biomédica^i l Dosimetry, Vienna, 10-14 March 1975, IAEA (1975).563. (18) HETTINGER PETTERSSON, . G , , SVENSSONC. , Dis, ,H. p lacement effect of thimble chambers exposed to a photon or electron beam fro betatrona m , Acta Radiologica 6 _1967( . 1 ) 6 ( 19) WAMBERSIE, A., DUTREIX, A., "RBE as a function of depth n higi h energy electro d photoan n n beams",Frontierf o s Radiation Therap d Oncologyan y , (VAETH, J.M. ,Ed) 2_Karger. ,S , Basel Yorw 1968Ne /( k ) 104,

103 C/ÎO) MNTIITFIJ , J. IJI.ANC, , I)., CASANOVAS , . DUTRKTX J , , WA. A, MUIRS, K I A., l'R1.0NOT,M , "N?suro . a l répartitio e d . a l dos o ed n :i ô \o öt e l n Plexigla n f , é i ln i un r r s i n s a d r u o d i : o f o r p n e c ô ; .- o p . àê par un faisceau d ' o l PC t rons monnc i né t iques de 10, 13, 20 t res S ., n y 0 , . r.io3 Mr i u(Tt.-ily) Le>d t n s V" Sy.ii l'ro o 2n d ö p. . r M r r i , 20-24 Oc.l-, 1969 o (1970- F , - F.urnlor,d )? ) " 437 i ' i ' ! . (.M) '.vAMBULiSlïî , OU'RK A. , ,j'RlOJOT A. , X T : . ResultatV , d s comparaiso l omiag a ' G L J s dosimotre e do rcenlo ed nt i s n ro . s n nioyoa o o 1'oSO . d Kiid. f. nF.lc . l J l o pouo r i , c t e l r 1973, _5£ , 835- 839. (22) AI. MOND, P . K . , I.AW, J., S Vïï.NS SON , II . : Comparisons of radiation dosiuiotry between Houston (U.S.A.), r j>u Eol hb n i(U.K. ) , P>i , . ) M? . y3 1972en l d .inec . 1 o e 5i v :, S 64-70 ( ,U17 ra oa . (23 Ol'I ) V TN Q^R, PFAT.ZNF. . R , R, P.M., KTSF.NT.OH , . MAT.Oi l R, , S.A., SAM KT.HVICI , A., NA CL , J . : The TARA program in medical radiation dos i 1=10 t ry , Aim . N.Y. Aca

~~104 TABLE I. Cb_ AND C,A VALUES FOR DIFFERENT ELECTRON AND PHOTON ENERGIES DETERMINED BY COMPARISON WITH FeSO,~~

~~Type of electron e Energth f o y e poinDeptth f to h C measured for a C h E generator incident electron of measurement (d) beam (E /MeV) Nuclear Enterprises recommended values (d/g.cm~2)(a) chamber~~

~~Allis-Chalmers (c) betatron 10.0 2. 0.881 + 0.008 0.895~~

~~"Sagittaire" linear accelerator 10.0 2.0 0.888 + 0.019 0.893~~