VITAL GUIDE

VITAL GUIDE SERIES Vital guide to radiography and radiation protection 16

● How is dental radiography used?

● How can radiation risks be minimised?

● What are the recommended techniques?

VITAL GUIDE TO Radiography and radiation protection

Stuart Grange* explains some of the key features of safe and effective dental radiography, and the legal requirements.

Dental radiography The fundamental aim of radiation protection Radiation effects In the dental setting, techniques exist for is to reduce risk of harm by ensuring that any imaging the teeth, mandible, maxilla, tempo- dose received is justifi ed and ‘as low as reason- Deterministic effects – the severity of romandibular joints and the oral and labial ably practicable’ (ALARP). the effect is related to the amount soft tissues. Virtually all dental practices will We may consider harmful effects from of exposure, and only occurs after a have one or more intra-oral units for peri- x-rays to fall into two types, determinis- certain threshold is exceeded. 1 apical, bitewing and occlusal radiography. tic or stochastic. For deterministic effects, Stochastic effects – the risk of the Many will have units for extra-oral radiog- the subject must be exposed to consider- effect is related to the amount of raphy such as dental panoramic tomography able amounts of radiation before any damage exposure. Theoretically, there is no and lateral cephalometry. A few centres may becomes apparent. Skin burns and cataracts maximum limit below which stochastic have cone beam computed tomography units, in the lens of the eye fall into this category. We effects, such as cancer induction, particularly where complex orthodontic and should never expect to observe these effects may occur. implant work is performed. from dental radiography due to the small We should never see deterministic Due to the risk of radiation induced injury amount of radiation used. Stochastic effects effects from dental radiography and or misdiagnosis from incorrectly produced include the development of cancer – a known we must seek to minimise the risk of images, radiography should only be under- potential outcome of exposure to ionising stochastic effects. taken by appropriately trained personnel and radiation. Increasing exposure is believed under well-designed systems of work. Max- to be associated with increasing risk, and imising diagnostic benefi t and minimising therefore there is no unequivocally safe radiation or from short-haul air fl ights. Per- radiation risk requires that practitioners are maximum dose. sons requesting and conducting radiographic judicious in their selection of techniques for Patients may ask about the risk from expo- investigations should be familiar with the each patient. sure to x-rays. Dental professionals physically size of doses from specifi c examination types. directing exposures should be able to give Table 1 shows typical dose from common Radiation protection information to the patient that helps them dental exposures. Radiation protection refers to the imple- set any risk from the exposure in context. mentation of practices to reduce radiation The risk of adverse effects from dental radi- Legislation governing exposure to patients, workers and the public. ography is very small, but it is inaccurate to medical radiography state that it is non-existent. It is helpful to There are two pieces of legislation which * Senior Lecturer in Diagnostic Imaging compare the risk from radiography to other embody the legal requirements for use of at the University of the West readily understood and accepted risks from ionising radiations in the UK: The Ionising of England, Bristol everyday life, for example, the amount of Radiation Regulations 1999 (IRR 99),3 and Email: [email protected] radiation received from natural background The Ionising Radiation (Medical Exposure) www.nature.com/vital vital 43 VITAL GUIDE

Table 1 Typical doses from dental radiography2,13 IR(ME)R 2000 key principles

Typical effective Equivalent period of natural Justification doses (mSv) background radiation Medical exposure to x-rays should always be justified. The person Teeth (single authorising (practitioner or operator) bitewing or 0.002 A few hours the exposure should anticipate periapical) a significant benefit to treatment decision-making from having Teeth (panoramic) 0.01 <1.5 days the information that the radiograph provides.

Optimisation Chest 0.02 3 days Where justification is present, the (single PA fi lm) amount of x-ray exposure used should be the smallest necessary to achieve Return fl ight 0.02 3 days a diagnostic image. IRR99 and IR(ME) to Spain R 2000 use the words ‘As low as reasonably practicable’ to express UK average background radiation = 2.2 mSv per year this concept.

Regulations 2000 (IR[ME]R 2000).4 Together that restrict exposure 1. Justification of exposure and they provide the legal framework to ensure • Regular maintenance. optimum selection of technique that risks from the use of ionising radiation An x-ray should only be taken where it is are minimised. IR(ME)R 20004 is primarily concerned likely to affect the patient’s dental man- The Regulations are of course written in the with protection of the patient. The princi- agement. General radiographic screening kind of legalese that is inaccessible for many ples of justifi cation and optimisation are core of new patients prior to clinical examina- people, and for that reason are accompanied to these regulations. IR(ME)R also identi- tion is not justifi ed.7 The radiograph taken by Approved Codes of Practice5 that help to fi es a number of roles of people involved should include only that which is required interpret the relevant features and legal obli- in exposing a patient to radiation. These to answer the diagnostic question. Selection gations. For dental radiography, the National help to ensure that an appropriate chain of of bitewings or periapical fi lms in preference Radiological Protection Board produced the responsibility exists when referring for and to panoramic fi lms is recommended where Guidance Notes for Dental Practitioners in undertaking radiography. these are likely to adequately demonstrate 2001.6 They are primarily intended to be used • Referrer – the registered medical or the problem. Dental radiography of pregnant as guidance by dental practitioners outside dental practitioner referring the patient patients is permissible so long as the exposure of the hospital sector, where access to medi- for radiography is justifi ed, and the dose kept to the practical cal physics experts is less readily available. • Practitioner – the registered medical minimum. Foetal doses from dental radiogra- All staff involved in radiography would ben- or dental practitioner that justifi es the phy are very small, and correspondingly, risk efi t from familiarity with these. They may exposure to x-rays as having suffi cient of foetal harm is extremely low.14 be downloaded from the Health Protection net benefi t Agency website. • Operator – the adequately trained person 2. Optimised equipment IRR 993 relates to the responsibilities of the permitted to undertake practical aspects Doses from dental radiography have come employer in ensuring safe working environ- of radiography. This may include direct down as equipment design and features have ments for employees and the general public. involvement with the x-ray exposure, improved.8 However, there is some evidence This is achieved by: processing the fi lm or carrying out quality that dental practices do not always take full • Appropriate restriction of personnel and assurance procedures. advantage of all the opportunities that exist to the public from areas where radiation is reduce dose.9 used by designation of ‘controlled areas’; In general dental practice, the dentist may practically in dental radiography this means undertake all three roles or may delegate the Rectangular collimation and outside of the primary x-ray beam and 1.5 role of operator to another adequately trained film holders metres away from the x-ray tube or patient dental care practitioner such as a nurse, A rectangular collimator reduces the beam in any other direction6 hygienist or therapist. dimensions in periapical and bitewing • Local rules which identify the controlled radiography (Fig. 1). The fi xed collimation area, persons entitled to operate Practical dose reduction of older intra-oral units is often circular the equipment and a summary of Doses to patients may be minimised in the giving a larger beam area than necessary for operating instructions following ways: rectangular fi lms. • Having a radiation protection supervisor; 1. Justifi cation of exposure and optimum A greater degree of accuracy is required a suitably trained member of staff who is selection of technique when using the rectangular collimator to suffi ciently senior that they have authority 2. Optimised equipment avoid ‘coning’, that is, missing part of the fi lm to ensure compliance with the local rules 3. Careful execution of technique with the beam. Accurate beam alignment • Presence of safety features on equipment 4. Quality assurance programme. with the fi lm is facilitated by the use of beam

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expressed in increasing numbers eg 100, 200, 400, 800 and so on. It is recommended that intensifying screens utilise rare earth tech- nology rather than older calcium tungstate to take advantage of the higher intensifying factor and thus reducing the dose required.

Digital radiography Digital radiography is able to accept a greater range of exposures and still produce Fig. 1 Rectangular collimator on an intra-oral Fig. 2 Film holder and film showing beam x-ray unit aiming ring a diagnostically acceptable radiograph. The operator may electronically manipulate the image with post-processing software to adjust contrast and brightness for optimum viewing. With fi lm radiography a signifi cant under or over exposure will probably result in a useless radiograph. Nevertheless, it is important that expo- sure times are adjusted to give only enough radiation to obtain a diagnostic image. Over- exposure of a digital detector is unlikely to result in an unacceptable radiograph, but gives an unacceptable dose since it is not as low as reasonably practicable. Manufacturers should be able to advise on the necessary level of exposure for adequate image formation.

3. Careful technique Careful technique includes: • Good communication with patient to let them know what is expected • Head immobilisation using head rest for intra-orals or chin rest and head clamp for panoramic fi lms • Correct positioning of fi lm and angulation of tubehead for intra-orals • Correct set up of anatomical planes for panoramic radiographs • Use of fi lm holders to help achieve the correct relationship of teeth, fi lm and beam • Correct exposure selection Fig. 3 Examples of exposure restriction in panoramic tomography • Removal of radiopaque objects prior to exposure. Earrings, necklaces, braces, spectacles will all cause obvious artefacts aiming devices such as fi lm holders (Fig. 2). be given to the limitation of the exposed area on the image, and may obscure They also confer image quality advantages: to only that portion of the dentition consid- important features. a) The fi lm is more parallel to the tooth ered relevant to the clinical problem under and allows a more reproducible and less investigation eg one quadrant, the anterior 4. Quality assurance programme distorted image to be taken. Periodontal teeth, the TMJs etc (Fig. 3). Quality assurance (QA) is an essential part of bone levels are far more accurately assessed dental radiography. The purpose of QA is to using paralleling as opposed to bisecting Film speed set standards according to the available evi- angle techniques The current recommendations are that an dence for best practice, to regularly audit that b) Most fi lm holders incorporate a stalk which intra-oral fi lm of at least E speed is used.6 If these standards are being met and to record is outside the mouth that allows accurate all other exposure factors are equal the use compliance. Implementation of QA pro- location of the x-ray beam to cover the fi lm of E or F speed fi lm results in a dose reduc- cedures allows identifi cation of equipment c) Used properly the fi lm is less likely to move tion relative to D speed fi lm of 45% and 60% problems, or working practices that are not than if held by the patient. respectively. The slight increase in image up to standard. These can then be corrected. graininess that results is not likely to affect the Beam limitation in diagnostic effi cacy of the image. a) Image quality panoramic tomography For extraoral radiographs using intensify- Every radiograph should be rated for qual- Where the facility exists consideration must ing screens, increasing speed of the system is ity and the rating recorded in patient notes to www.nature.com/vital vital 45 VITAL GUIDE

Image evaluation schools within the UK. The National Exam- that the risk to all from x-rays is kept as low ining Board for Dental Nurses administrates as possible. 1 Excellent . No errors of patient the nationally recognised exam leading to the preparation, exposure, positioning, Certifi cate in Dental Radiography entitling 1. Whaites E. Radiography and radiology processing or film handling. them to take radiographs unsupervised.11 for dental nurses. Edinburgh: Churchill It is expected that all dental professionals Livingstone, 2005. 2 Diagnostically acceptable. Some errors of patient preparation, involved in requesting or taking radiographs 2. Patient Dose information http://www.hpa. exposure, positioning, processing should be updated every fi ve years on the org.uk/web/HPAweb&HPAwebStandard/ 6 or film handling, but which do not use of ionising radiation. A QA programme HPAweb_C/1195733826941 detract from the diagnostic utility of should note the date of the last update and 3. The Ionising Radiation Regulations. the radiograph. when another is due. As well as reiterating London: HMSO, 1999. important principles in radiation protection, 4. The Ionising Radiation (Medical 3 Unacceptable . Errors of patient preparation, exposure, positioning, updates should expose practitioners to up- Exposure) Regulations. London: The processing, or film handling, which to-date guidance that helps ensure they are Stationery Offi ce, 2000. render the radiograph diagnostically using the best practice as it is understood at 5. Ionising Radiation Regulations 1999. unacceptable. Errors should be the time. Approved code of practice L121. Sudbury: identified and film retaken. Adequate training on individual pieces HSE Books, 1999. of equipment is essential since it cannot be 6. NRPB. Guidance notes for dental assumed that an understanding of one sort of practitioners on the safe use of X-ray identify if there are consistent problems. A 1-3 equipment will transfer to the use of another. equipment. Chilton: National Radiological scale has been suggested for this purpose.6 Dental panoramic tomography is particularly Protection Board, 2001. susceptible to compromise of image quality http://www.hpa.org.uk/web/ b) Patient dose and x-ray equipment due to machine-based variations. Practition- HPAweb&HPAwebStandard/ Typical doses (diagnostic reference levels) ers should be trained in the use of equipment HPAweb_C/1195733764370 for particular examinations should not be by an experienced and suitably qualifi ed 7. FGDP (UK). Selection criteria for dental exceeded. Regular maintenance and testing of member of staff, or by the manufacturer; radiography. London: Royal College of equipment to ensure correct functioning of most will provide staff training as part of Surgeons of England, 1998. warning lights and audible alarms, and stable the sales package negotiated at the time 8. Gulson A D, Knapp T A, Ramsden P G. radiation output should help to ensure this. of purchase. Doses to patients arising from dental The HPA offers a Radiation Protection Service None of the training described above is x-ray examinations in the UK, 2002-2004. for dentists that will assist in complying with deemed suffi cient to enable practitioners Chilton: Health Protection Agency, 2007. the Regulations.10 to operate cone beam CT equipment. The 9. Davies C, Grange S, Trevor M M. Health Protection Agency recommends at Radiation protection practices and c) Darkroom, films and processing least half a day’s training from the manufac- related continuing professional education Poor quality fi lm handling and processing will turer or other well qualifi ed person such in dental radiography: a survey of negate any advantages from good technique as dento-maxillofacial radiologist or practitioners in the North-east of England. if the resultant image quality is compro- specialist radiographer.12 Radiography 2005; 11: 255-261. mised. Processing is one of the most obvious 10. Radiation Protection Service for Dentists. areas that will benefi t from a well thought e) Audit www.hpa.org.uk/radiation/services/dxps out QA programme. Processors must be reg- Audit is the basis on which the effectiveness of 11. NEBDN Certifi cate in Dental Radiography. ularly serviced, checked for light tightness a QA programme is verifi ed. The date of audit http://www.nebdn.org/dental_ and undergo regular cleaning of rollers and and its outcome should be recorded within an radiography.html chemical tanks. Solutions should be tested, audit record. Regular assessment of how well 12. Holroyd J R, Gulson A D. The radiation to ensure the correct strength of developer an establishment matches up to its own stand- protection implications of cone beam and fi xer, and be changed when necessary. ards will allow defi ciencies to be identifi ed computed tomography in dentistry. Chilton: Film should be stored in a cool, dry place and and remedial action to be taken. Frequency of Health Protection Agency, 2009. rotated to ensure that older stock is used fi rst. individual aspects of QA must be established 13. Langland O E, Langlais R P, Preece J locally based on accepted norms, but over- W. Principles of dental imaging, 2nd ed. d) Training all review of the QA programme as a whole Baltimore: Williams and Wilkins, 2002. IR(ME)R 20004 stipulates that all practi- should be conducted not less than annually 14. Documents of the Health Protection tioners and operators involved in exposing to ensure that it continues to be effective and Agency. Protection of pregnant patients patients to x-rays must be ‘adequately trained’. includes up-to-date practices. during diagnostic medical exposures to Schedule 2 of these regulations details aspects ionising radiation. Health Protection of radiation science and practice as are Conclusion Agency, The Royal College of Radiologists, deemed relevant for safe radiography. Radiography is an essential tool in clinical The College of Radiographers, 2009. Qualifi ed dentists receive their training diagnosis and treatment decision-making. in dental radiography as part of their BDS Extensive legislation exists to protect the Radiography and radiation protection is a qualifi cation. Dental nurses, hygienists and patient, public and workers. Careful applica- core CPD topic. To take part in Vital verifi able therapists may access approved training tion of the Ionising Radiation Regulations CPD and complete the questions based on this courses provided by the British Dental Asso- together with the employment of best prac- article, turn to page 56 for instructions on how ciation, and certain dental and radiography tices in radiation protection help to ensure to subscribe.

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