CRITERIA FOR ACCEPTABILITY OF RADIOLOGICAL, NUCLEAR MEDICINE AND RADIOTHERAPY EQUIPMENT
FINAL DRAFT AMENDED-V1.4-091001
EUROPEAN COMMISSION CONTRACT NO. TREN/07 /NUCL/S07.70464
Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
FOREWORD (TO BE WRITTEN BY THE CEC)
Notes that may be useful aide memoir for Foreword:
Background to directives
Key points to be mentioned by the Commission
Key changes
More detailed report, extended in length from about 20 to over 100 pages.
Much more explicit attention to Radiotherapy and Nuclear Medicine.
Definition creep. Use of Suspension Levels (redefined) as key component of definition. Evidence base for criteria, and their classification according to evidence base. Some areas not as developed as we would have liked and evidence base for criteria in short supply.
Inclusion of process for dealing with exceptions including rapidly changing technology.
Harmonisation with requirements of MDD.
New: More explicit statements of process to be used for application of Criteria in practice.
The Commission is grateful to Dr Keith Faulkner who coordinated the overall project and to Professor Jim Malone (Introduction and Diagnostic Radiology Lead), Dr Stelios Christofides (Nuclear Medicine Lead) and Professor Stephen Lillicrap (Radiotherapy Lead), who coordinated the work in the specialist areas indicated.
Page 2 of 104 FOREWORD TO ORIGINAL DOCUMENT
The work of the European Commission in the field of radiation protection is governed by the Euratom Treaty and the Council Directives made under it.
The most prominent is the Basic Safety Standards Directive (BSS) on the protection of exposed workers and the public (80/836/Euratom) revised in 1996 (96/29/Euratom).
In 1984 Council issued a complementary Directive to the BSS on the protection of persons undergoing medical exposures (84/466/Euratom) revised in 1997 (97/43/Euratom).
Both Directives require the establishment by the Member States of criteria of acceptability of radiological (including radiotherapy) installations and nuclear medicine installations.
Experience showed that drawing up such criteria, especially as regards the technical parameters of the equipment, sometimes created difficulties.
Therefore in 1990, the Commission took the initiative to develop examples of criteria of acceptability (Bland, N.R.P.B.).
Following two constructive meetings with competent authorities of the Member States (18/9/1992 and 30/3/1994) a need for extension to specific radiological and nuclear medicine installations was forwarded. In 1995 an inquiry among competent authorities was made (Kal & Zoetelief) to make an evaluation of the existing situation resulting in a new report suggesting additional criteria for these installations.
This report, amended with data from other sources, was discussed with competent authorities in Luxembourg on 4 and 5 September 1996.
The result is a flavour of criteria of acceptability applicable to facilities in use for radiology, radiotherapy and nuclear medicine. These criteria are not binding to the Member States but were prepared to assist competent authorities in their task to establish or to review criteria of acceptability, also called minimum criteria. They should not be confused with the requirements for design and construction of radiological and nuclear medicine equipment as mentioned in annex I, part 2, § 11,5 of the Council Directive on medical devices (93/42/EEC).
This report will be reviewed on a regular basis in order to take into account new scientific and technical data as appropriate.
It forms part of a series of technical guides on different subjects developed to facilitate the implementation of the Directive on medical exposures. It is my hope that the document will help to ensure continuing improvement in radiation protection in the medical field.
Suzanne FRIGREN Director Nuclear Safety and Civil Protection
Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
CONTENTS
FOREWORD (To be written by the CEC) ______2 FOREWORD TO ORIGINAL DOCUMENT ______3 CONTENTS ______4 1. INTRODUCTION ______6 1.1. Purpose and Background ______6 1.2. Basis for Criteria of Acceptability in European Directives ______8 1.2.1. Requirements of the Medical Exposure Directive ______8 1.2.2. Wider context, the MDD Directive and Equipment Standards ______10 1.3. To whom this document is addressed ______12 1.4. Criteria of Acceptability ______13 1.4.1. Approaches to Criteria ______13 1.4.2. Suspension Levels ______14 1.4.3. Identifying and Selecting Criteria ______16 1.5. Special Considerations, Exceptions and Exclusions ______18 1.5.1. Special Considerations ______18 1.5.2. Exceptions ______19 1.5.3. rapidly evolving technologies ______19 1.5.4. Exclusions ______20 1.6. Establishing criteria of acceptability have been met ______20 2. DIAGNOSTIC RADIOLOGY ______23 2.1. Introduction ______23 2.2. X-Ray Generators and equipment for General Radiography ______24 2.2.1. Introduction ______24 2.2.2. Criteria for X-Ray Generators, and General Radiography ______27 2.3. Radiographic Image Receptors and Viewing Facilities ______30 2.3.1. Introduction ______30 2.3.2. Criteria for Image Receptors and Viewing Facilities ______32 2.4. Mammography ______38 2.4.1. Introduction ______38 2.4.2. Measurements ______39 2.5. Dental Radiography ______42 2.5.1. Introduction ______42 2.5.2. Intra-Oral Systems ______42 2.5.3. Criteria for Dental Radiography ______43 2.5.4. Panoramic radiography ______44 2.5.5. Cephalometry ______44 2.6. Fluoroscopic Systems ______45 2.6.1. Introduction ______45 2.6.2. Criteria for Acceptability of Fluoroscopy Equipment ______46 2.7. Computed Tomography ______47 2.7.1. Introduction ______47 2.7.2. Criteria for Acceptability of CT Systems ______49 2.8. Dual Energy X-ray Absorptiometry ______50 2.8.1. Introduction ______50 2.8.2. Acceptability Criteria for DXA Systems ______50 3. NUCLEAR MEDICINE EQUIPMENT ______51
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3.1. Introduction ______51 3.2. Nuclear Medicine Therapeutic Procedures ______53 3.2.1. Introduction ______53 3.2.2. Activity Measurement Instruments ______54 3.2.3. Contamination Monitors ______54 3.2.4. Patient Dose Rate Measuring Instruments ______55 3.2.5. Radiopharmacy Quality Assurance Programme ______56 3.3. Radiopharmacy for Gamma Camera based Diagnostic Procedures ______57 3.3.1. Introduction ______57 3.3.2. Activity Measurement Instruments ______58 3.3.3. Gamma Counters ______58 3.3.4. Thin Layer Chromatography Scanners ______59 3.3.5. Contamination monitors ______59 3.4. Radiopharmacy for Positron Emission Based Diagnostic Procedures ______60 3.3 Gamma Camera based Diagnostic Procedures ______60 3.3.1 Introduction ______60 3.4.1. Planar Gamma Camera ______61 3.4.2. Whole Body IMAGING System ______62 3.4.3. SPECT System ______63 3.4.4. Gamma Cameras used for Coincidence Imaging ______64 3.5. Positron Emission Diagnostic Procedures ______65 3.5.1. Introduction ______65 3.5.2. Positron Emission Tomography System ______66 3.5.3. Hybrid Diagnostic Systems ______67 3.4 Intra-Operative Probes ______68 4 RADIOTHERAPY ______70 3.6. Introduction ______70 3.3 Linear accelerators ______71 3.7. Simulators ______74 3.8. CT Simulators ______77 3.9. Cobalt-60 units ______80 3.10. Kilovoltage Units ______82 3.11. Brachytherapy ______83 3.12. Treatment Planning Systems ______84 3.13. Dosimetry Equipment ______85 3.14. Radiotherapy Networks ______86 APPENDIX 1 INFORMATIVE NOTE ON IMAGING PERFORMANCE ______89 APPENDIX 2 AUTOMATIC EXPOSURE CONTROL ______90 APPENDIX 3 EQUIPMENT ______91 REFERENCES & SELECTED BIBLIOGRAPHY ______93 ACKNOWLEDGEMENTS ______104
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1. INTRODUCTION
1.1. PURPOSE AND BACKGROUND
The purpose of this publication is to specify minimum performance standards for radiological, nuclear medicine and radiotherapy equipment. The criteria of acceptability presented here are based on levels of performance that prompt intervention and will result in the use of the equipment being curtailed or terminated, if not corrected. The criteria are produced in response to Directive 97/43/Euratom, which requires that medical exposures be justified and carried out in an optimized fashion. To give effect to this Directive, Article 8.3 stipulates that Member States shall adopt criteria of acceptability for radiological equipment in order to indicate when action is necessary, including, if appropriate, taking the equipment out of service. In 1997, the Commission published Radiation Protection 91: Criteria for acceptability of radiological (including radiotherapy) and nuclear medicine installations (EC, 1997), in pursuit of this objective. This specified minimum criteria for acceptability and has been used to this effect in legislation, codes of practice and by individual professionals throughout the member states and elsewhere in the world.
RP 91 considered diagnostic radiological installations including conventional and computed tomography, dental radiography, and mammography, radiotherapy installations and nuclear medicine installations. However, development of new radiological systems and technologies, improvements in traditional technologies and changing clinical/social needs have created circumstances where the criteria of acceptability need to be reviewed to ensure the principles of justification and optimization are upheld. To give effect to this, the Commission, on the advice of the Article 31 Group of Experts, initiated a study aimed at reviewing and updating RP 91 (EC, 1997), which in due course has led to this publication.
This revised publication is, among other features, intended to:
1. Update existing acceptability criteria.
2. Update and extend acceptability criteria to new types of installations. In diagnostic radiology, the range and scope of the systems available has been greatly
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extended (e.g. computed radiography, digital radiography, digital fluoroscopy, multislice computed tomography (CT) and dual energy x-ray absorptiometry (DXA)). In nuclear medicine, there are Positron Emission Tomography (PET) systems and hybrid scanners. In radiotherapy, there are linear accelerators with multileaf collimators capable of intensity modulated radiotherapy (IMRT).
3. Identify an updated and more explicit range of techniques employed to assess criteria of acceptability,
4. Provide criteria that have a reasonable opportunity of being accepted, and that are achievable throughout the member states.
5. Deal, where practical, with the implications for screening techniques, paediatrics, high dose techniques and other special issues noted in the 1997 Directive.
6. Promote approaches based on an understanding of and that attempt to achieve consistency with those employed by the Medical Devices Directive (MDD) (Council Directive 93/42/EEC), industry, standards organizations and professional bodies.
7. Make practical suggestions on implementation and verification.
To achieve this, the development and review process has involved a wide range of individuals and organizations, including experts from relevant professions, professional bodies, industry, standards organizations and relevant international organizations. It was easier to achieve the last objective with radiotherapy than with diagnostic radiology. This is because of a long tradition of close working relationships between the medical physics and international standards communities, which has facilitated the development and adoption of common standards in radiotherapy. An attempt has been made, with the cooperation of the International Electrotechnical Commission (IEC), to import this approach to the deliberations on diagnostic radiology and to extend it, where it already exists, in nuclear medicine.
The intent has been to define parameters essential to the assessment of the performance of radiological medical installations and set up tolerances within which the technical quality and equipment safety standards for medical procedures are
Page 7 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment ensured. The methods for performance assessment recommended generally rely on non-invasive measurements open to the end user. This publication will benefit the holder of radiological installations, bodies responsible for technical surveillance and authorities charged with verifying compliance of installations with regulations on grounds of technical safety. However, it is important to bear in mind that the present publication follows the precedent established in RP 91, is limited to the equipment and does not address wider issues such as those associated with, for example, the requirements for buildings and installations, information technology (IT) systems such as picture archiving and communication systems (PACS) and/or radiological information systems (RIS).
1.2. BASIS FOR CRITERIA OF ACCEPTABILITY IN EUROPEAN DIRECTIVES
1.2.1. REQUIREMENTS OF THE MEDICAL EXPOSURE DIRECTIVE
The work of the European Commission in the field of radiation protection is governed by the Euratom Treaty and the Council Directives made under it. The most prominent is the Basic Safety Standards Directive (BSS) on the protection of exposed workers and the public (Council Directive 80/836/Euratom), revised in 1996 (Council Directive 96/29/Euratom). Radiation protection of persons undergoing medical examination was first addressed in Council Directive 84/466/Euratom. This was replaced in 1997 by Council Directive 97/43/EURATOM (MED) on health protection of patients against the dangers of ionizing radiation in relation to medical exposure. This prescribes a number of measures to ensure medical exposures are delivered under appropriate conditions. It makes necessary the establishment of quality assurance programmes and criteria of acceptability for equipment and installations. These criteria apply to all installed radiological equipment used with patients.
The directive also deals with the monitoring, evaluation and maintenance of the required characteristics of performance of equipment that can be defined, measured and controlled. In particular, it requires that all doses arising from medical exposure of patients for medical diagnosis or health screening programmes shall be kept as low as reasonably achievable consistent with obtaining the required diagnostic
Page 8 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment information, taking into account economic and social factors (ALARA). Specifically, the requirements in respect of criteria of acceptability are stated as follows:
“Competent authorities shall take steps to ensure that necessary measures are taken by the holder of the radiological installation to improve inadequate or defective features of the equipment. They shall also adopt specific criteria of acceptability for equipment in order to indicate when appropriate remedial action is necessary, including, if appropriate, taking the equipment out of service.”
Additional requirements in respect of image intensification and dose monitoring systems are explicitly specified. These extend to all new equipment which:
“shall have, where practicable, a device informing the practitioner of the quantity of radiation produced by the equipment during the radiological procedure.”
Finally Article 9 requires that:
“Appropriate radiological equipment ----- and ancillary equipment are used for the medical exposure
of children,
as part of a health screening programme,
involving high doses to the patient, such as interventional radiology, computed tomography or radiotherapy.”
And that:
“Special attention shall be given to the quality assurance programmes, including quality control measures and patient dose or administered activity assessment, as mentioned in Article 8, for these practices.”
Practical consequences of these requirements are that:
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1. Acceptance testing must be carried out before the first use of the equipment for clinical purposes to ensure it complies with its performance specification and to provide reference values for future performance testing.
2. Further performance testing must be undertaken on a regular basis, and after any major maintenance procedure.
3. Necessary measures must be taken by the holder of the radiological installation to improve inadequate or defective features of the equipment.
4. Competent authorities must adopt specific criteria of acceptability for equipment in order to indicate when appropriate action is necessary, including taking the equipment out of service.
5. Appropriate quality assurance programmes including quality control measures must be implemented by the holder of the radiological installation.
This publication deals with the first four points and will be germane to some aspects of the fifth. It updates and extends the advice provided in 1997 in RP 91 (EC, 1997). However, this document is not intended to act as a guide to quality assurance or quality control programmes, which are comprehensively dealt with elsewhere (CEC 2006; APPM 2006a, b; IPEM 2005a, b; AAPM 2002; BIR 2001; Seibert 1999; IPEM, 1997a, b, c).
1.2.2. WIDER CONTEXT, THE MDD DIRECTIVE AND EQUIPMENT STANDARDS
Since 1993, safety aspects of design, manufacturing and placing on the market of medical devices are dealt with by MDD. It is managed by the European Directorate General Enterprise; its main goal is to define and list the Essential Requirements, which must be fulfilled by Medical Devices. When such a device is in compliance with the Essential Requirements of the MDD, it can be “CE marked”, which opens the full European market to the product.
There are a number of ways with which manufacturers can demonstrate that their products meet the Essential Requirements of the MDD; the one of most interest here involves international standards. Further, demonstration of conformity with the
Page 10 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment essential requirements must include a clinical evaluation. Any undesirable side- effects must constitute an acceptable risk when weighted against the performance intended. For the types of system that are the subject of this publication, demonstration of the essential requirements can be achieved by the procedures described in the directive annexes. Conformity of all or part of these requirements can be demonstrated or verified through compliance with harmonised international standards. These are standards that specify essential requirements for the basic safety and essential performance of the device, such as those issued by the IEC or Comité Européen de Normalisation Electrotechnique (CENELEC).
Although the MDD includes requirements for devices emitting ionising radiation, this does not affect the authorisations required by the directives adopted under the Euratom treaty when the device is brought into use. In this regard, the Euratom Treaty directives have precedence over the MDD. Conformity with an IEC or CENELEC standard will frequently be included as part of the suppliers‟ specification and will be confirmed during contractual acceptance (acceptance testing) of the equipment by the purchaser. On the other hand the acceptability criteria in this publication must be met during the useful life of the equipment and its compliance with them will generally be regularly assessed.
The MDD was substantially amended by Directive 2007/47/EC. The amendments include an undertaking by the manufacturer to institute and keep up to date a systematic procedure to review experience gained from devices in the post- production phase and to implement appropriate means to apply any necessary corrective action. Furthermore, the clinical evaluation and its documentation must be actively updated with data obtained from the post-market surveillance. Where post-market clinical follow-up as part of the post-market surveillance plan for the device is not deemed necessary, this must be duly justified and documented.
In transposing these European directives into national law, the acceptability criteria required by the MED may be transposed into national law using country specific criteria and approaches. It is clear that this may undermine the applicability essential performance standards as required by the MDD or through compliance with the international standardisation system. Such an approach conflicts with the concept of free circulation and suppression of barriers to trade, which is one of the goals of the
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EU in general and the MDD in particular. To avoid these difficulties there is an urgent and clear need for harmonisation between the requirements of the two directives (MDD and MED). Thus it is desirable that all EU countries both transpose the MED requirement for criteria of acceptability in a consistent fashion that will not harm the efforts under the MDD, the standards and CE marking systems, to ensure free circulation of goods and suppress trade barriers. The approach advocated in this publication is consistent with this objective.
Thus, care must be exercised transposing the requirements of the MED based on either partial or inappropriate adoption of this publication as national legislation. Where this is envisaged, some caution is necessary and due discretion must be allowed in respect of the clinical situations envisaged in this introduction and the associated technology specific sections. Furthermore, adopting a regulation based solely on national radiation protection considerations without due regard for the issues arising from the MDD is likely to prove counterproductive for both suppliers and end users. At a national level, the solution adopted should ensure patient safety while fostering a cooperative framework between industry, standards, end users and regulators. Internationally, there is a clear need for harmonization and a level of uniformity between countries in recognition of the global nature of the equipment supply industry. It is further necessary that there be harmonization between industry and users, at least in terms of the methodologies employed.
1.3. TO WHOM THIS DOCUMENT IS ADDRESSED
Regulatory documents and standards, with respect to equipment performance, can be addressed to or focused primarily on the needs or obligations of a particular group. For example, the standards produced by IEC and CENELEC are primarily aimed at manufacturers and suppliers. Many of the tests they specify are type tests that could not be done in the field.
However, the possible audiences for this publication include holders, end users, regulators, industry and standards organizations. It is recognized that each of these has a necessary interest in this publication and its application. It was recognized that the primary audience for the publication is the holders and end-users of the equipment (specifically, the health agencies, hospitals, other institutions,
Page 12 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment practitioners, medical physicists and other staff and agents, who deploy the equipment for use with patients). In addition, it was recognized that it must reflect the requirements of regulators when they are acting in the medical area in the interests of end users and/or patients. This is in keeping with the precedent implicitly established through the scope and format adopted for RP 91. This publication addresses the needs of these groups while taking due account of the reality of globalization of the industry, standards and the harmonization objectives viz a viz the MDD noted elsewhere. The technical parts of Sections 2, 3, and 4 assume those reading and using them are familiar with this introduction and have a good working knowledge of the relevant types of equipment and appropriate testing regimes.
1.4. CRITERIA OF ACCEPTABILITY
1.4.1. APPROACHES TO CRITERIA
Approaches to describing the acceptability and performance of equipment have varied. They inevitably include requirements specifically prescribed in the directive, such as:
“In the case of fluoroscopy, examinations without an image intensification or equivalent techniques are not justified and shall therefore be prohibited”, or,
“Fluoroscopic examinations without devices to control the dose rate shall be limited to justified circumstances.”
With respect to other areas, they range from provision of hard numerical values for performance indices to detailed specification of measurement methodologies without indicating the performance level to be accepted. The latter approach has come to be favoured in many of the standards issued by bodies like IEC or CENELEC and by some professional bodies.1 While this approach has the advantage that it is
1 The IEC is the world's leading organization that prepares and publishes International Standards for all electrical, electronic and related technologies. IEC standards cover a vast range of technologies, including power generation, transmission and distribution to home appliances and office equipment, semiconductors, fibre optics, batteries, and medical devices to mention just a few. Many, if not all, of the markets involved are global. Within the EU CENELEC is the parallel standards organization and in practice adopts many IEC standards as its own aligning them within the European context.
Page 13 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment easier/possible to get consensus on it among the manufacturers, professions and other interests involved, it also has some disadvantages. These include an evident lack of transparency, associated limitations on accountability and risks of misapplication in the hands of inexperienced users.
A comprehensive, consistent suite of approaches to performance and safety assessment of radiological equipment has been proposed by the UK Institute of Physics and Engineering in Medicine (IPEM, 2005a, b; IPEM, 1997a, b, c]. The American Association of Physics in Medicine (AAPM,, 2006a, b, 2005, 2002) and British Institute of Radiology (BIR, 2001) have also, among other professional organizations, published much useful material. The IPEM system is based on the assumption that deviations from the baseline performance of equipment on installation will provide an adequate means of detecting unsafe or inadequately performing equipment. This approach is questionable within the meaning of criteria of acceptability in the MED; if the baseline is, for one reason or another, unsatisfactory, there are no criteria on which it can be rejected. In light of this issue, the approach more recently favoured by IPEM and many standards organizations has not been adopted in most instances. Where possible, the emphasis has been to propose firm suspension levels. This is consistent with the approach adopted in many countries, including, for example, France, Germany, Belgium, Spain, Italy, Luxembourg and others which have adopted hard limits for performance values based on RP 91 or other sources.
1.4.2. SUSPENSION LEVELS
A critical reading of the directive, RP 91 and the professional literature reveals some shift or “creep” in the meaning of the terms remedial and suspension level since they came into widespread use in the mid 1990s. In the interest of clarity, we have redefined them in a way that is consistent with both their usage in the Directive and their current usage, as follows:
Definition of Suspension Levels:
A level of performance that requires the immediate removal of the equipment from use.
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Following a documented risk assessment involving the Medical Physics Expert (MPE) and the practitioner, the suspended equipment may be considered for use in limited circumstances. The holder and the operators must be advised in writing of the suspension and/or the related limitation(s) in use. 2
A suspension level not being met requires that the equipment is taken out of service immediately. Not meeting the level makes the equipment unsafe, or performance so poor, that it would be unacceptable to society. The level is based on minimum standards of safety and performance that would be acceptable in the EU and represent the expert judgement of the working group and reviewers based on their knowledge of what is acceptable among their peers and informed by the social, legal and political circumstances that prevail in the EU. When suspension levels are reached the equipment must be removed from use (or restricted in use) with patients, either indefinitely or until it is repaired and again satisfies the criteria.
It is also possible that the equipment will pass an evaluation based on suspension levels but be unsatisfactory in some other way. This may be because we have mainly considered suspension levels as performance tolerances (particularly in radiotherapy) whereas equipment may very well fail on safety issues which are covered by the IEC general standards 60601-1 (IEC, 2003b) and associated collateral and particular standards. Many quality assurance manuals refer to the levels triggering such actions as remedial levels. In line with the precedent established in RP 91 (EC, 1997), the main thrust of this publication is concerned with suspension levels. Remedial levels are, on the other hand, well described in numerous quality assurance publications detailing them (AAPM, 2005; IPEM, 2005a, b; AAPM, 2002; EC, 1997, IPEM, 1997a, b, c; et al).
Suspension levels are taken as the criteria of acceptability. They must be clearly distinguished from the levels set for acceptance tests. The latter are used to establish that the equipment meets the supplier‟s specification or to verify some other contractual issue; they may be quite different from the criteria of acceptability
2 Examples of how this might arise include the following: 1.In radiotherapy, a megavoltage unit with poor isocentric accuracy could be restricted to palliative treatment until the unit could be replaced. 2. In nuclear medicine, a rotational gamma camera with inferior isocentric accuracy could be restricted to static examinations. 3. In diagnostic radiology, an x-ray set with the beam limiting device locked in the maximum field of view position might be used to expose films requiring that format in specific circumstances.
Page 15 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment envisaged in the directive. However, it is entirely possible that equipment meeting the requirements of the acceptance test will automatically pass the criteria of acceptability. This is because the acceptance test for modern equipment will often be more demanding than the criterion of acceptability. Tests based on the criteria of acceptability should be performed on installation and thereafter regularly or after major maintenance.
In practice, acceptability testing should assure the equipment tested is serviceable and provides acceptable clinical image quality using acceptable patient radiation doses. QA testing may involve additional elements beyond the acceptability and will inevitably involve reporting many remedial levels. It is presumed that by the time acceptability is considered, acceptance tests, compliance with manufacturer‟s specifications and commissioning tests have been successfully performed. Equipment may be significantly reconfigured during its useful life arising from updating, major maintenance or changes in its intended use. If this is done, appropriate new acceptability tests will be required.
1.4.3. IDENTIFYING AND SELECTING CRITERIA
It was not possible to devise a single acceptable approach to proposing values or levels for the criteria selected. Instead a number of approaches, with varying degrees of authority and consensus attaching to them, have been adopted and grouped under headings A to D as follows:
Type A Criterion
This type of criterion is based on a formal national/international regulation or an international standard.
A reasonable case can sometimes be made for using a manufacturer‟s specification as a criterion of acceptability. For example, all CE marked equipment, which meets specification, will either meet or exceed the essential safety standards with which the equipment complies. Thus, testing to the manufacturer‟s specification could be taken as a means of ensuring the criteria of acceptability are met or exceeded in the area they address.
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A case can also be made that compliance with the relevant IEC, CENELEC or national standards might be taken as compliance with criteria that the industry has deemed to be essential for safety. In practice, this approach may be limited in value as the tests required may not be within the competence of end users or service engineers in the field. Thus different agreed approaches to verification will be required. Development in this area is essential to the harmonization referred to above. In particular, agreed methodology is essential in any system of equipment testing. Standards organizations provide a useful role model in this regard, which this publication has tried to emulate.3
Type B Criterion
This type of criterion is based on formal recommendations of scientific, medical or professional bodies.
Where industrial standards are not available or are out of date, advice is often available from professional bodies, notably IPEM, AAPM, NEMA, BIR, ENMS, ACR et al. More detailed advice on testing individual systems is available from the AAPM, earlier IPEM publications and a wide range of material published by many professional bodies and public service organizations. Much of the material is peer reviewed and has been a valuable source where suitable standards are not available.
Type C Criterion
This type of criterion is based on material published in well established scientific, medical or professional journals.
Where neither standards nor material issued by professional bodies are available, the published scientific literature has been consulted and a recommendation from the drafting group has been proposed and submitted to expert review by referees. Where this process led to a consensus, the value has been adopted and is recommended below.
3 When equipment standards are developed so that their recommendations can be addressed to and accepted by both “manufacturers and users”, the question of establishing criteria of acceptability becomes much simplified. Highly developed initiatives in this regard have been undertaken in radiotherapy (see IEC 60976 and IEC 60977). These “provide guidance to manufacturers on the needs of radiotherapists in respect of the performance of MEDICAL ELECTRON ACCELERATORS and they provide guidance to USERS wishing to check the manufacturer‟s declared performance characteristics, to carry out (footnote continued)
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Type D Criterion
The Type D situation arises where it has not been possible to make a recommendation. In a small residue of areas it has not been possible to make recommendations for a variety of reasons. For example, where the technology involved is evolving rapidly, listing a value could be counterproductive. It could become out of date very rapidly or it could act as an inhibitor of development. In such situations we feel the criterion of acceptability should be determined by the institution holding the equipment based on the advice of the MPE or Radiation Protection Adviser (RPA) as appropriate.
The criteria of acceptability proposed are identified as belonging to one or another of these categories. In addition, at least one reference to the primary source for the value and the method recommended is provided. Some expansion on the approach and the rationale for the choice is provided, where deemed necessary in an Appendix. Test methods are only fully described if they cannot be referred to in a high quality accessible reference.
1.5. SPECIAL CONSIDERATIONS, EXCEPTIONS AND EXCLUSIONS
1.5.1. SPECIAL CONSIDERATIONS
The directive requires that special consideration be given to equipment in the following categories:
Equipment for screening,
Equipment for paediatrics and
High dose equipment, such as that used for CT, interventional radiology, or radiotherapy.
acceptance tests and to check periodically the performance throughout the life of the equipment”. This approach has much to offer other areas.
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The chapters and sections in the attached volumes dealing with the high dose group (CT, interventional radiology or radiotherapy), deal comprehensively with this requirement.
Equipment used for paediatrics and in screening programmes is often similar or possibly identical to general purpose equipment. Where this is the case, additional guidance for the special problems of paediatrics, such as the requirement for a removable grid in general radiology or fluoroscopy and the special needs with regard to CT exposure programmes are noted in the technology specific sections. The special requirements for mammography are based on those appropriate to screening programmes.
1.5.2. EXCEPTIONS
Exceptions to the recommended criteria may arise in various circumstances. These include the cases cited in Section 1.2 above, where equipment compliant with safety and performance standards that predate the criteria for acceptability has to be assessed. In such cases, the MPE should make a recommendation to the end user or holder, on whether or not this level of compliance is sufficient to meet the intentions of the directive. These recommendations must take a balanced view of the overall situation, including the economic/social circumstances, older technology etc.; they may be nuanced in that the RPA/MPE may recommend that the equipment be accepted subject to restrictions on its use. Likewise it is always well to remember that acceptability criteria, as already outlined, may depend on the use(s) for which equipment is deployed.
1.5.3. RAPIDLY EVOLVING TECHNOLOGIES
Medical imaging is an area in which many new developments are occurring. Encouragement of development in such an environment is not well served by the imposition of rigid criteria of acceptability. Such criteria, when rigorously enforced, could become obstacles to development and thereby undermine the functionality and safety they were designed to protect. In such circumstances, the MPE should recommend to the end-user a set of criteria that are framed to be effective with the new technology and that takes account of related longer established technologies,
Page 19 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment any IEC/CEN/CENELEC standards available, the manufacturer‟s recommendations, the related scientific and professional opinion/published literature and the maxim that the new technology should aspire to be at least as safe as existing technology it is replacing.
1.5.4. EXCLUSIONS
Within this publication, the term “equipment” has been interpreted to mean the main types of equipment used in diagnostic radiology, nuclear medicine and radiotherapy. This follows the precedent established in RP 91 (EC, 1997). It is important to be aware that the full installation is not treated. Thus, the requirements for an acceptable physical building and shielding that will adequately protect staff, the public and, on occasions, patients; power supplies and ventilation have not been addressed. However, this is an area of growing concern and one in which the requirements have changed considerably as both equipment and legislation have changed. In addition the acceptable solutions to the new problems, arising from both equipment development and legislation, in different parts of the world, are different. Consequently, this area is now in need of focused attention in its own right.
Likewise, the contribution of IT networks to improving or compromising equipment functionality can bear on both justification and optimization. This can apply to either PACS or RIS networks in diagnostic radiology and imaging, planning and treatment networks in radiotherapy centres. The requirements for acceptability of such networks are generally beyond the scope of this publication, although they have been included occasionally, for example in radiotherapy, where they are integral to the treatment.
As already mentioned elsewhere, the publication focuses on criteria of acceptability and it does not offer advice intended for use in routine Quality Assurance programmes.
1.6. ESTABLISHING CRITERIA OF ACCEPTABILITY HAVE BEEN MET
The criteria of acceptability will be applied by the competent authorities in each member state. The authorities for the MED are generally not the same as those for
Page 20 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment the MDD. In addition the criteria will be introduced and applied in the context of the unfolding requirements for clinical audit in healthcare in general and in the radiological world in particular. This is accompanied by a general increase in the requirements for individual and institutional accreditation. Thus the holder of radiological equipment should appoint a competent person to establish that the criteria of acceptability have been met. The person appointed should be an MPE or a person of similar standing. Who performs the tests to verify compliance is a matter for local arrangements. Thus the MPE may choose to perform the tests themselves, write them up, report on them and sign them off. Alternatively, he/she may accept results provided by the manufacturer‟s team. These may have been acquired, for example, during acceptance testing or commissioning. Results for tests performed to agreed methodology will be satisfactory in many cases. They provide the information on which the MPE can make a judgement on whether or not the equipment meets the criteria. These two approaches represent the extremes. Most institutions will establish a local practice somewhere between that allows the criteria to be verified with confidence by a suitably qualified agent acting on behalf of the end user. In radiotherapy, joint acceptance testing by the manufacturer‟s team and the holder‟s MPE is commonplace. Whichever approach is taken, where a suspension level is not met, the outcome and any associated recommendations from the MPE and/or the practitioner must be communicated promptly, in writing, to both the holder and the operators/users of the equipment.
In situations where the formally recommended criteria of acceptability are incomplete, lack precision, or where the equipment is very old, subject to exception, special arrangements or exemptions, the judgement and advice of the MPE becomes even more important. Additional, more complete, measurements may be needed to determine the cause of the change in performance. When equipment fails to meet the criteria, agreement must be established on how it will be withdrawn from use with patients. This must be done in association with the MPE whose advice must be obtained. The options, in practice, include those mentioned above and include the possibility of immediate withdrawal, where the failure of compliance is serious enough to warrant it. Alternatively a phased withdrawal or limitations on the range of use of the equipment may be considered. In the latter case, the specific circumstances under which the equipment may continue to be used must be carefully
Page 21 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment defined and documented. In addition, the advice of the MPE to the practitioner and/or the holder or the holder‟s representative must be made available in a prompt and timely way, consistent with the recommendations for action.
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2. DIAGNOSTIC RADIOLOGY
The technical parts of Sections 2, 3, and 4 assume those reading and using them are familiar with the introduction and have a good working knowledge of the relevant types of equipment and appropriate testing regimes.
2.1. INTRODUCTION
Since RP 91 (EC, 1997), there have been a number of major developments in diagnostic radiology. Perhaps the key new developments are the introduction of direct digital detectors (e.g. large area flat panel detectors) for use in radiology and fluoroscopy, as well as multiple slice computed tomography scanners. Both these new developments have implications for acceptability criteria, but suspension levels in these areas are less mature.
Manufacturers have also incorporated information technology and other developments into medical imaging systems which have resulted in radiological imaging equipment being more stable. For instance, the stability of the applied tube potential produced by high frequency generators has been much improved when compared with previous x-ray generator designs (e.g. single phase). As equipment performance evolves, so do acceptability criteria.
With the implementation of the quality culture within radiology departments and the evolution of quality assurance programmes, criteria have also changed. In part the availability of instrumentation for determination of radiation exposure in radiology linked to computers has also impacted on measurement approaches and quality assurance.
However, in rapidly evolving areas of radiology, such as CT scanning, acceptability criteria have not kept pace with technological developments. There is a deficit in consensus based acceptability criteria for these areas of practice which will need to be addressed in the future. Acceptability criteria for all types of diagnostic radiology equipment are summarised in the following sections.
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2.2. X-RAY GENERATORS AND EQUIPMENT FOR GENERAL RADIOGRAPHY
2.2.1. INTRODUCTION
General radiographic systems still provide the great majority of X-Ray examinations. They may be subdivided in practice into a number of subsidiary specialist types of system. This section deals with the Suspension Levels applicable to X-Ray generators, and general radiographic equipment. It also includes or is applicable to mobile systems, traditional conventional tomography and tomosynthesis systems, system subcomponents/devices such as automatic exposure control (AEC), and grids. Much of what is presented here is also applicable to generators for fluoroscopic equipment. However, the criteria have not been developed with specialized X-ray equipment in mind: dental, mammographic, CT and DXA units are mentioned in sections 2.4, 2.5, 2.7, and 2.8.
The criteria here refer to X-ray tube and generator, output, filtration and half value layer (HVL), beam alignment, collimation, the grid, AEC, leakage radiation and dosimetry. Suspension/tolerance levels are specified in the Tables below. Before presenting them a few aspects of half value layer and filtration, image quality, paediatric concerns, AEC, mobile devices, and spatial resolution must be mentioned to ensure that the approach and the Tables are interpreted correctly.
HVL/filtration
Total filtration in general radiography should not normally be less than 2.5 mm Al. The half value layer (HVL) is an important metric used as a surrogate measurement for filtration. It shall not be less than the values given in Table 2.1.
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Table 2.1 Minimum half-value layer (HVL) requirements Application Values of x-ray tube Minimum permissible (HVL) in mm Al voltage. (kV) (IEC 60601-1-3 (IEC, 2008a) and see Notes 1 and 2) General <50 See note 3 radiography x- 50 1.8 ray equipment 60 2.2 70 2.5 80 2.9 90 3.2 100 3.6 110 3.9 120 4.3 >120 see note 3 Note 1: These HVLs correspond to a total filtration of 2.5 mm Al for equipment operating at constant potential in tungsten anode. Note 2: Linear extrapolation to be used here. Note 3: Test methods differ for different modalities.
Paediatric Issues
Requirements for radiography of paediatric patients differ from those of adults, partly related to differences in size and immobilization during examination (see notes in Tables throughout Section 2). Beam alignment and collimation are particularly important in paediatric radiology, where the whole body, individual organs and their separation distance are smaller. The x-ray generator and tube must have sufficient power to make short exposure times possible. In addition the option to remove the grid from a radiography table/image receptor is essential in a system for paediatric use, as is the capacity to disable the AEC and use manual factors. Systems used with manual exposures (like dedicated mobile units for bedside examinations) should have exposure charts for paediatric patients.
Image Quality and Spatial Resolution
There are unresolved difficulties in determining objective measures of image quality that are both reproducible and reflect clinical performance. Measurements here are limited to high
Page 25 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment contrast bar patterns, and may be augmented by subjective or semi subjective assessments at the discretion of the MPE and the Practitioner. (Appendix 1)
Automatic exposure control for any radiographic detector
The AEC should provide limitation of under- and overexposure of the receptor and exposure time. Digital generators also require that pre-programmed exposure systems be assessed to ensure acceptability based on the suppliers‟ specification and the MPE‟s evaluation. It may also, at the discretion of the MPE, and subject to its being an agreed part of the equipment specification with the supplier, include assessment of Ka,e for a specific type of examination (see Table 2.2 below for radiographic detectors (method in
Appendix 2). This should be such that the Ka,e for the patient phantom is below an agreed diagnostic reference level (DRL). In addition, the optical density of the film should be between 1.0 and 1.5 OD (SBHP-BVZF, 2008).
Table 2.2 Examples of image receptor Ka,e for various examinations for some specific conditions see note 1 Examination Image receptor entrance air PMMA Tube kerma (incl. back scatter) thickness (cm) voltage
Ka,e (μGy) (kVp) Abdomen radiograph adult) 5 20 80 Chest radiograph (adult) 5 11 120 Chest radiograph (child) 5 8 80
Note 1: For method see Appendix 2; this also includes some information on CR and DDR.
Mobile devices
For mobile devices the criteria for equipment for general radiography are applicable except the requirements for alignment, which cannot be met in practice.
Conventional tomography
The parameters for conventional tomography equipment include cut height level, cut plane incrementation, exposure angle, cut height uniformity and spatial resolution.
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2.2.2. CRITERIA FOR X-RAY GENERATORS, AND GENERAL RADIOGRAPHY
Table 2.3: Criteria for Acceptability of General Radiography Systems Physical Parameter Suspension Level Reference Type Notes (Paediatrics) Mechanical and If defects pose an IEC 60601 A Mechanical and electrical safety immediate mechanical Series electrical safety or obvious electrical failures can be the hazard to patients or source of accidents staff X-RAY SYSTEM x-ray tube and generator tube voltage A Lower kVp often used accuracy in paediatrics (EC, 1996c) Dial calibration Maximum deviation: > EC (1997) A ± 10% or ± 10 kV IPEM (2005a) B Variation with tube Maximum variation: > EC (1997) B current ± 10% Precision of tube Deviation > ± 5% from EC (1997) A voltage mean x-ray tube output Magnitude of output Y(1m) > 25 μGy/mAs EC (1997) A at 80 kV and 2.5 mm Al Consistency of output Y within ± 20% of EC (1997 ) B mean IPEM (2005a) Consistency of output Y within ± 20% of IPEM (2005a) B for range of qualities mean Half-value layer (HVL ) /total filtration HVL or sufficient total HVL in excess for IEC (2008) A Additional Cu filtration filtration values in Table 8.1 0.1 or 0.2 mm (EC, 1996c) (A) Exposure time Consistency of Actual exposure time EC (1997) A Consistency and exposure time > IPEM (2005a) B absolute values ± 20% of indicated required for shorter value for values > exposures, 100ms particularly in paediatrics (EC, 1996c) Alignment x-ray/light beam Sum of misalignment IPEM (2005a) B alignment in principle directions
> 3% of dFID
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Orthogonality of x-ray The angle between EC (1997) A beam and image central beam axis and receptor (IR) IR ≤ 1.5º from 90º Collimation Collimation of x-ray x-ray beam within EC (1997) A beam borders of image receptor Automatic collimation X-ray beam shall not EC (1997) A differ by more than
2% of dFID at any side of image receptor Borders within IR Grid A Grids preferably not to be used with children (EC, 1996c) Grid artefacts No artefacts should be EC (1997) A visible Moving grid Lamellae should not EC (1997) A be visible on image AEC verification See also Appendix 2 Focal spot (FS) size A Smaller sizes may be through assessment required for various of spatial resolution applications including paediatrics (EC, 1996c) Spatial resolution Spatial resolution ≥ JORF (2007a) B DIN standard (limited by FS size 1.6 lp/mm and detector characteristics) Limitation of Maximal focal spot EC (1997) A Much equipment is overexposure charge < 600 mAs non compliant in practice.Should this be modified. Limitation of exposure Maximum exposure EC (1997) A time time: 6s
Consistency of AEC Ka may not differ by SBPH-BVZ B See also Appendix 2 unit more than 10% from (2008) mean value
Verification of Ka,e at See table 2.2. SBPH-BVZ B See also Appendix 2 image receptor for 1.0 < OD >1.5 (2008) reference examination Verification of sensors Film density for each SBPH-BVZ B For chest of AEC sensor may not differ (2008) examinations sensors by more than 0.2 OD are different on from mean value purpose. See also Appendix 2 Verification of AEC at Film density for a SBPH-BVZ B See also Appendix 2 Page 28 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment various phantom phantom thickness (2008) thicknesses differs by more than 0.3 OD from mean value for all thicknesses Verification of AEC at Film density at a tube SBPH-BVZ B See also Appendix 2 various tube voltages voltage may not differ (2008) by more than 0.2 OD from mean value for all tube voltages Dose to plate in CR ≥ 10 μGy/plate Walsh et al C NOTE: This is double and DDR Systems (2008.) the max normally under AEC encountered (3-5 uGy/plate). Grid in position for this measurement. AEC performance in > 50%* Walsh et al C * >50% variation CR and DDR (2008) allowed for 5 cm Systems: PMMA. Leakage radiation
Leakage radiation Ka(1m) < 1mGy in one EC (1997) A hour at maximum rating Dosimetry For KAP meters see 2.6 Image quality Spatial better than 2.8 DIN 6868-58 B Use phantom lp/mm for dose < 10 (2001) described in the μGy. standard And better than 2.4 lp/mm for dose < 5 μGy. Contrast All seven steps are DIN 6868-58 B Use phantom not visible (2001) described in the standard
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Table 2.4: Criteria for Acceptability of Conventional Tomography Systems
Physical Parameter Suspension Level Reference Type
Cut height level Difference between indicated and measured EC (1997) A value < 5 mm
Cut plane incrementation Reproducibility cut height < 2 mm EC (1997) A
Exposure angle Indicated and measured angle should agree EC (1997) A within 5° for angles more than 30°. Agreement better for smaller angles
Cut height uniformity Image should reveal no overlaps, EC (1997) A inconsistencies of exposures, or asymmetries in motion
Spatial resolution Resolution < 1.6 lp/mm EC (1997) A
2.3. RADIOGRAPHIC IMAGE RECEPTORS AND VIEWING FACILITIES
2.3.1. INTRODUCTION
The Criteria of Acceptability and the related suspension/tolerance levels for X-Ray Films, Screens, Cassettes, CR, DR, Automatic Film Processors, the Dark Room, Light Boxes and the Environment for general radiography are presented in Tables 2.5 to 2.12 below. They do not deal with the requirements for mammography or dental radiography.
A wider approach to Quality Assurance of film, film processing and image receptors of all types is a critical part of an overall day to day quality system (IPEM, 2005a; BIR, 2001, IPEM, 1997a; Papp, 1998). Such a system includes commissioning. Detailed commissioning tests are covered in other publications (IPEM, 1997a).
There are some fundamental differences between CR and film/screen systems. Proper installation and calibration of a CR system in a radiology department is extremely important. It is also important to note that the x-ray system needs to be properly set up so that it may
Page 30 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment be used with CR plates. In particular, the AEC needs to be appropriately set up (Section 2.2).
Details on desirable specifications and features of CR systems as well as their proper installation can be found in AAPM Report No 93 (2006a). These guidelines should be followed prior to the acceptability testing of CR systems. To date, unlike film systems, there is little guidance on the performance of CR systems, and the suspension/tolerance levels identified will almost inevitably need adjustment in line with future evidence and guidance (Section 1.4).
Likewise, with DDR systems, the tube and generator, workstation and /or laser printer must be known to be working properly. When undertaking the QA of the tube and generator, it is advisable to keep the detector out of the beam or protected by lead. As with CR little guidance is available on Suspension/Tolerance levels and the advice given above for CR prevails. Suspension/ tolerance levels suitable for application at the present time are provided in Table 2.7.
Display monitors and hardcopy images have a crucial role in the diagnostic process. IPEM notes that inadequacies in the imaging viewing area may serve to negate the benefits of other efforts made to maintain quality and consistency. Modern radiology departments require digital images from many modalities and from PACS systems to be viewed in many locations. Two classes of display are used: diagnostic (systems used for the interpretation of medical images) and review (viewing medical images for purposes other than for providing a medical interpretation). The requirements for each are different.
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2.3.2. CRITERIA FOR IMAGE RECEPTORS AND VIEWING FACILITIES
Table 2.5 Criteria of Acceptability for Automatic Film Processors, Films, Screens, Darkrooms and Illuminators (mammography excluded) Physical Parameter Suspension Reference Type Notes Level Automatic Film Processor: Base plus Fog OD > 0.3 IPEM (2005a) B See also IEC 61223- IPEM (1997a) 2-1 (1993c), Papp (1988) and EC (1997) Speed Index 1.2 ± 0.3 IPEM (2005a) B See also IEC 61223- BIR (2001) 2-1 (1993c) and IPEM (1997a) Papp (1988). Contrast Index 1.0 ± 0.3 IPEM (2005a) B See also IEC 61223- BIR (2001) 2-1 (1993c) and IPEM (1997a) Papp (1988). Films, Screens, Darkroom and Illuminators: Screens and Visible artefacts. IPEM (2005a) B See also IEC 61223- Cassettes BIR (2001) 2-2 (1993d) and EC IPEM (1997a) (1997). Relative Speed of > 10% or IPEM (2005a) B See also EC (1997). Intensifying Screens > 0.3 OD across IPEM (1997a) film. Film Screen Contact Non-uniform IPEM (1997a) B See also IEC 61223- density or loss of 2-2 (1993d) and EC sharpness. (1997). Dark Room Safe Evidence of film IPEM (2005a) B See also IEC 61223- Lights and Film fogging after twice BIR (2001) 2-3 (1993e). fogging the normal Film AAPM (2002) Handling Time. Ambient Lighting > 100 Lux. IPEM (1997a) B See also Papp (1988), EC (1997).
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Table 2.6 Criteria for Acceptability of Cassettes and Image Plates: Physical Parameter Suspension Level Reference Type Notes Condition of Damage to plate IPEM (2005a) B Suppliers‟ cassettes and image recommendations for plates method Uniformity Gross non-uniformity IPEM (2005a) B 70kV, 1.0 mm copper Mean ± 20% at tube head, an exposure for 10µGy, read plate under linear algorithm.
Table 2.7 Criteria for Acceptability of CR readers see notes 1 and 2 Physical Parameter Suspension Level Reference Type Notes Dark Noise Agfa SAL>130 AAPM (2006a) B Erase plates, leave Fuji pixel value > 280 plates 5 minutes, read
Kodak EIGP > 80 under standard
Kodak EIHR > 380 conditions. Konica pixel value < Repeat for all plate 3975 sizes. Linearity and system Manufacturer‟s KCARE (2005a) B KCARE CR QA. transfer properties specification Establish system transfer properties equation (STP) Dose=f(pixel value) Erasure cycle Blocker visible in IPEM (2005a) B High attenuation efficiency second image material Exposure index Indicated exposure KCARE (2005a) B Record detector dose consistency does not agree with indicator and calculate measured exposure indicated exposure within 20% using the STP equation for all plates Detector dose The variation in the KCARE (2005a) B indicator consistency calculated indicated exposures differs by greater than 20% between plates for a same exposure Scaling errors > 2% IPEM (2005a) B Blurring Blurring present KCARE (2005a) B Use contact mesh Image quality High Spatial resolution DIN 6868-58 A,C Use phantom described Contrast Resolution better than 2.8 lp/mm (2001) in the standard. Also (Limiting Spatial for dose < 10 μGy. note AAPM, 2006a & Resolution) ≥ 2.4 lp/mm for dose < Walsh et al. 2008 5 μGy. Contrast All seven steps visible DIN 6868-58 A,C Use phantom described (2001) in the standard
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Low-Contrast Manufacturers AAPM (2006a) B Low contrast resolution Resolution specifications test object Laser beam function Edge not continuous AAPM (2006a) B Steel ruler the full length of the image Moiré Patterns Moiré Patterns visible KCARE (2005a) B 70kV, 1.0mm of copper at tube head, grid in place, plate in the bucky at 150cm from the focus
1. The suspension values quoted for Dark Noise were valid at the time of Publication of this document. However as CR is an evolving technology they are subject to change. 2. This is a test that has to be done during the acceptance testing of the CR Reader in order to establish the relationship between receptor dose and pixel value. It tests whether the X-ray generator and the CR reader have been properly set up in order to work together correctly.
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Table 2.8 Criteria of Acceptability for DDR systems see notes 1, 2 Physical Suspension Level Reference Type Notes Parameter Dark Noise Excessive noise in the IPEM (2005a ) B Image without system exposure or very low exposure Linearity Manufacturers KCARE (2005b) C Establish system recommendation transfer properties equation (STP) Dose=f(pixel value) Image retention Ghosting present KCARE (2005b) C Low exposure with closed collimators and detector covered with lead apron. Exposure Index Indicated sensitivity KCARE (2005b) C 70kV, 1.0 mm copper indices differ by greater at tube head, at least than 20% of equivalent three times for 10 exposure sets. µGy. Repeat for 1 µGy and 12 µGy
Uniformity Mean ± 5% IPEM (2005a) B 70kV, 1.0 mm copper at tube head, 10 µGy. Scaling errors >2% IPEM (2005a) B Grid, attenuating object of known dimensions or lead ruler Uniformity of Blurring present IPEM (2005a) B Use fine wire mesh resolution Image quality High Spatial resolution better DIN 6868-58 A,C Use phantom Contrast than 2.8 lp/mm for dose (2001) described in the Resolution < 10 μGy. standard. Also note (Limiting Spatial ≥ 2.4 lp/mm for dose < AAPM (2006a) & Resolution) 5 μGy. Walsh et al. (2008) Contrast All seven steps are DIN 6868-58 A,C Use phantom visible (2001) described in the standard
1. This test should be done at the acceptance testing of the DDR system in order to establish the relationship between receptor dose and pixel value. This is the relationship between the generator and the detector.
2. It should be noted that a number of manufacturers have installed on their DDR equipment automatic QA software in order to carry out a number of QA tests.
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Table 2.9 Criteria of Acceptability for Diagnostic Monitors Physical Parameter Suspension Level Reference Type luminance ratio <200 IPEM (2005a) B AAPM (2006a) luminance ratio Black baseline ±35% IPEM (2005a) B White baseline ±30% AAPM (2006a)
Distance and angle calibration – 10% IPEM (2005a) B distortion (for CRT) RCR (2002) SEFM-SEPR (2002) Resolution Visual inspection low IPEM (2005a) B and high contrast AAPM (2006a) resolution different from baseline DICOM greyscale GSDF ±15% IPEM (2005a) B (GSDF= DICOM Grayscale AAPM (2006a) Standard Display Function) Uniformity >40% IPEM (2005a) B AAPM (2006a) Variation between adjacent >40% IPEM (2005a) B monitors AAPM (2006a) RCR (2002) Room illumination >25 lux IPEM (2005a) B AAPM (2006a)
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Table 2.10 Criteria of Acceptability for Printers Physical Parameter Suspension Level Reference Type Notes Optical density Baseline ±0.30 IPEM (2005a) B Note also AAPM consistency BIR (2001) (2006a) IEC (1994a) Image uniformity >10% IPEM (2005a) B Note also AAPM (2006a)
Table 2.11 Criteria of Acceptability for Film Scanners Physical Parameter Suspension Level Reference Type Grayscale >10% Halpern (1995) C Lim (1996) Meeder et al (1995) Seibert (1999) Trueblood (1993) SEFM-SEPR (2002) Image uniformity >10% Halpern (1995) C Lim (1996) Meeder et al (1995) Seibert (1999) Trueblood (1993) SEFM-SEPR (2002) Distortion >10% Halpern (1995) C Lim (1996) Meeder et al (1995) Seibert (1999) Trueblood (1993) SEFM-SEPR (2002) Spatial resolution Visual inspection low and Halpern (1995) C high contrast spatial Lim (1996) resolution different from Meeder et al (1995) baseline Seibert (1999) SEFM-SEPR (2002)
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Table 2.12 Criteria of Acceptability for Viewing Boxes Physical Parameter Suspension Level Reference Type Notes Luminance < 1000 cd/m2 IPEM (2005a) B IEC (1993f) Mammography < 3,000 cd/m2 > 6,000 cd/m2 Uniformity >30% IPEM (2005a) B IEC (1993f) Mammography < 30% Variation between adjacent >30% IPEM (2005a) B IEC (1993f) viewing boxes Mammography < 15% Room illumination (general >150 lux IPEM (2005a) B IEC (1993f) radiography) Room illumination >50 lux CEC (2006) A IEC (1993f) (mammography)
2.4. MAMMOGRAPHY
2.4.1. INTRODUCTION
Mammography involves the radiological examination of the breast using x-rays. Mammography is primarily used for the detection of breast cancer at an early stage and is widely used in screening programmes involving healthy populations. It is also used with symptomatic patients. Early detection of breast cancer in a healthy population places particular demands on the radiological equipment as high quality images are required at a low dose. Perhaps because of the exacting demands of mammography, acceptability criteria are particularly well developed (IPEM, 2005b; CEC, 2006).
Mammography should be performed on equipment designed and dedicated specifically for imaging breast tissue. Either film/screen or digital detectors may be used. The minimum features of a mammography unit are described in table 2.13. Table 2.14 summarises the acceptability criteria for conventional mammography equipment and 2.15 those for digital units.
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Table 2.13 Minimum Specification of an X-ray Unit Designed for mammography Aspect Specification Broad focus 0.3 (IEC, 2003a) X-ray Tube Nominal Focal Spot Small focus 0.15 Adjustable or automatically adjusted position AEC (Analogue Equipment) Fine control of optical density Motorized Compression Readout of compression thickness Grid Moving (dedicated mammography) Focus Film Distance ≥ 60cm
2.4.2. MEASUREMENTS
Measurements to assess the performance of mammography units should be performed using a series of test equipment, some of which are specifically designed for the purpose.
Specific Tests are outlined in the tables below. The purpose of the test and a recommended protocol are cited, together with alternative acceptable protocols. These should form part of a quality system (BSI, 1994).
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Table 2.14 Film Screen Mammography
Physical Parameter Suspension Level Reference Type Notes Not correctable Target Film Density OD<1.3 or >2.1 IPEM (2005a) B by AEC fine control mAs > ±5% Variation in mAs AEC Consistency CEC (2006) A < Maximum deviation in OD ≥ CEC (2006) AEC Thickness 0.15 from value at 4cm of A AFFSAPS Compensation PMMA or range of ODs > B (2007) 0.35 Film/Screen Contact >1 cm² poor contact CEC (2006) A High Contrast < 12lp/mm CEC (2006) A Resolution Threshold Contrast > 1.5% 5-6mm CEC (2006) A
X-ray/Film Alignment > 5mm CEC (2006) A Maximum Force > 300N 200N not achievable by Compression CEC (2006) adjustment of manual A control. > 2kV difference from set Tube Potential IPEM (2005a) B value. HVL See Table 2.16 CEC (2006) A Compression Force > 20N CEC (2006) A In 30S Consistency
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Table 2.15 Digital Mammography Systems Physical Suspension Level Reference Type Notes Parameter AEC Consistency mAs>±5% baseline CEC (2006) A CNR/PMMA Thickness, with the value at 5cm being used as reference, values at AEC Thickness other thicknesses are 2.0cm >115% CEC (2006) A Compensation 4.5cm >103% 3.0cm >110% 5.0cm > 100% 4.0cm >105% 6.0cm > 95% 7.0cm > 90% > 0.85% 5-6mm > 2.35% Threshold Contrast CEC (2006) A 0.5mm > 5.45% 0.25mm X-ray/Film >5mm CEC (2006) A Alignment Maximum Force > 300N and IPEM (2005a) B Compression 200N not reachable. CEC (2006) A Tube Potential > 2kV difference from set value. IPEM (2005a) B Accuracy HVL See Table 2.16 CEC (2006) B Compression > 20N CEC (2006) A In 30S Force Consistency
Table 2.16 Typical HVL measurements for different tube voltage and target filter combinations. (Data includes the effect on measured HVL of attenuation by a PMMA compression plate*) (CEC, 2006) HVL (MM Al) for target filter combination kV Mo +30 m Mo Mo +25 m RH RH +25 m RH W +50 m RH W +0.45 m Al 25 0.33 ± 0.2 0.40 ± .02 0.38 ± .02 0.52 ± .03 0.31 ±.03 28 0.36 ± .02 0.42 ± .02 0.43 ± .02 0.54 ± .03 0.37 ±.03 31 0.39 ± .02 0.44 ± .02 0.48 ± .02 0.56 ± .03 0.42 ± .03 34 0.47 ± .02 0.59 ± .03 0.47 ± .03 37 0.50 ± .02 0.51 ± .03
* Some compression paddles are made of Lexan, the HVL values with this type of compression plate are 0.01 mm Al lower compared with the values in the table.
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2.5. DENTAL RADIOGRAPHY
2.5.1. INTRODUCTION
Dental radiography, though often delivering a low dose, is the most frequently conducted type of x- ray examination. This section is applicable to radiographic systems for intra oral radiography using both film and digital detectors.
2.5.2. INTRA-ORAL SYSTEMS
The following are not acceptable for dental imaging:
- Nominal or actual tube voltage < 60kVp for DC and 65-70Kvp for AC equipment
- Mechanical timers
- Film class lower than E
- Focus skin distance for intra oral equipment < 20cm.
- Non-rectangular collimators
- Systems without audible exposure indication.
Material and results of testing dental equipment are available in Gallagher et al. (2008), EC (1997), IEC standards, and the criteria for dental equipment adopted by EU member states (Belsuit van het FANC, 2008; IPEM, 2008; Luxembourg Annexe 7, 2008; JORF, 2007; IEC, 2000a; IPEM, 2005a; Directive R-08-05, 2005; SEFM-SEPR, 2002).
Where exposure settings or pre-programmed exposure protocols are provided with the equipment, their appropriateness should be checked as part of the confirmation that the equipment is acceptable. A distinction should be made between exposure settings for adults and children.
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2.5.3. CRITERIA FOR DENTAL RADIOGRAPHY
Table 2.17 Criteria of Acceptability for Intra-Oral Dental Equipment
Physical parameter Suspension level Reference (type) Type Notes Film development Developer temperature <18°C and > 40°C IPEM (2005a) B Use Luxembourg Thermometer Annexe 7 (2008) Dark room (or desktop Gross fog > 0.3 OD IPEM (2005a) B Densitometer day light processor) light proof Reproducibility of gross Gross fog > 0.3 OD; IPEM (2005a) B Densitometer; fog, speed and contrast X-ray tube and generator Tube voltage accuracy Maximum deviation JORF (2007) A kV meter, ± 10% Indication of exposure Difference between IPEM (2005a) A, B Dosimeter time measured exposure EC (1997) time and baseline > 50% Consistency of EC (1997) A Dosimeter??? exposure time Dosimetry
Incident air kerma for Ka > 4mGy JORF (2007) A Measurement upper molar tooth Luxembourg of incident air Annexe 7 (2008) kerma at the tip of the collimator
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2.5.4. PANORAMIC RADIOGRAPHY
This section is applicable to radiographic systems for panoramic dental radiography.
Table 2.18 Criteria for Acceptability of OPG Systems
Physical Parameter Suspension Level Reference Type Notes Image quality Characteristics of the Outside manufacturer‟s D Follow panoramic image specification manufacturer‟s specifications and test object Dosimetry Kerma area product of a Deviation > 35% of JORF A KAP meter or typical clinical exposure indicated PKA value. (2007) equivalent or calculated kerma dosimeter. area product from dose width product or equivalent
2.5.5. CEPHALOMETRY
This section is applicable to radiographic systems for cephalometry. In addition, cephalometric systems should:
- have X-ray beams collimated to the detector and not larger than 24cmx30cm - have at least a distance of 150cm between focus and skin
Table 2.19 Criteria for Acceptability of Cephalometry Systems Physical parameter Suspension level Reference Type Notes Dosimetry 2 Kerma area product of a typical PKA > 80 mGycm JORF (2007) A PKA meter or clinical exposure Luxembourg equivalent Annexe 7 (2008)
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2.6. FLUOROSCOPIC SYSTEMS
2.6.1. INTRODUCTION
Fluoroscopic systems can be highly flexible and are open to a wide range of applications. They may offer a multiplicity of modes (and sub-modes) of operation. A representative subset of the most probable intended uses of the equipment should be identified for acceptability testing. For example, the main “cardiac mode(s)” and associated sub-modes might be tested in a unit whose intended application will be in the area of cardiac imaging. If the unit is later deployed for different purposes the need for a new acceptability test will have to be considered by the practitioner and the MPE.
In many cases fluoroscopic systems are supplied as dedicated units suitable for cardiac, vascular, gastrointestinal or other specific applications. Powerful mobile units are available and are generally flexible. In all cases the MPE will have to consider the intended application of the unit and the environment in which it will be installed and used. With respect to the X-Ray generator, many of the criteria of acceptability are similar to those prevailing for general radiographic systems.
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2.6.2. CRITERIA FOR ACCEPTABILITY OF FLUOROSCOPY EQUIPMENT
Table 2.18 Criteria of Acceptability for Fluoroscopy and Fluorography Equipment Physical Suspension Level Reference Type Notes Parameter Mechanical – If defects pose an IEC (2003b) A 38 cm for fixed Safety immediate mechanical CRCPD (2002) fluoro or obvious electrical- 30 cm for mobile shock (hazard to fluoro patients or staff) 20 cm for special surgical fluoro Collimation Limits Irradiated area > 1.15 × IEC (2000b) A Use radiography imaged area Half-value layer Table 2.1 applies IEC (2000b) A Test methods are modality specific Patient Air Kerma The four rows BELOW IPEM (2005a, 2002) C The four rows Rates, and Image are SENTINEL Martin et al (1998) BELOW are receptor input Air VALUES offered for Dowling et al (2008) SENTINEL Kerma Rates consideration O‟Connor et al VALUES offered for (2008) consideration
“Patient” Entrance > 50 mGy/min O‟Connor et al C Normal mode Dose Rate, Fluoro (2008) smallest field size. Mode: (Image Dowling et al (2008) 20 cm water or Intensifier and FPD equivalent. Systems.) > 100 mGy/min Normal mode, any field size. Maximum (lead) “Patient” Entrance > 2mGy/exposure. O‟Connor et al C IPEM and Martin Dose/exposure (2008) protocols. Largest Digital Acquisition Dowling et al (2008) field size. 20 cm Mode (Image Cardiac Systems: > water or equivalent. Intensifier and FPD 0.2mGy/exposure Normal from survey Systems.) is 0.03 – 0.12 mGy/exposure) Detector Entrance > 1 μGy/sec in O‟Connor et al C 2 μGy/sec quoted Dose Rate, Fluoro continuous fluoroscopy (2008) in IPEM but not mode :(Image mode. Dowling et al (2008) seen in practice. Intensifier and FPD IPEM protocols. Systems). Cardiac Systems: > Largest field size. 1μGy/sec in continuous Normal mode. fluoroscopy mode. Detector Entrance > 5μGy/exposure. O‟Connor et al C Normal from survey Dose/exposure (2008) 0.06 – 0.2 Digital Acquisition Dowling et al (2008) μGy/exposure
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Mode :(Image Cardiac Systems: IPEM protocols. Intensifier and FPD >0.5μGy/exposure. Largest field size. Systems.) Integrated “dose If absolute accuracy IEC (2000b) A meter” calibration > ±35 % High contrast Spatial Resolution: < 1 IPEM (2005a) B Largest Field Size. resolution and lp/mm. focal-spot For Cardiac Systems: < 1.2 lp/mm Low contrast Threshold Contrast: > IPEM (2005a) B Largest Field Size. detectability 4% Systems or modes Radiographic generator See also Section 2.2 A of operation output conditions. controlled by As above for High manually setting X- Contrast resolution and ray factors low-contrast detectability. Fluoroscopic Timer Acoustic alert is not See also Section 2.2 A functional or not continuous until reset.
2.7. COMPUTED TOMOGRAPHY
2.7.1. INTRODUCTION
CT examinations are among the highest dose procedures encountered routinely in diagnostic radiology and account for up to 70 percent of diagnostic medical irradiation. Thus it is important both in terms of individual examinations and population effects. The design and proper functioning, and particularly the optimal use of equipment can substantially influence CT dose. This can be particularly important when pregnant patients or children are involved. CT scanners are under continual technical development resulting in increasing clinical application (Nagel, 2002). In the last two decades the development of helical and multidetector scanning modes allowed greatly enhanced technical abilities and clinical application (Kalender, 2000).
CT scanners may be replaced for reasons that, in theory, include poor equipment performance as demonstrated by failure to meet acceptability criteria. In practice it is also likely that replacement may frequently be with a view to meeting increased demands on the service, or to take advantage of new developments which enable improved diagnostics,
Page 47 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment faster throughput or other clinical benefits. In practice there are few (if any) examples of CT scanners being removed from use on the basis of their failure to meet currently accepted criteria of acceptability. This suggests that these criteria are ineffective or that obsolescence due to rapid technological development can be an overwhelming consideration in equipment replacement. Arising from these observations it is possible that the available criteria, including those which follow, should be viewed with caution. A review of the dose parameters or dose to patients for certain key procedures, and their comparison to accepted diagnostic reference levels, is a more meaningful measure of the acceptability of the practice using the CT scanner, but this is outside of the scope of the current document.
CT scanners are increasingly utilised in radiotherapy in support of treatment planning (Mutic, 2003; IPEM, 1999). They are also a component of PET-CT systems and CT acceptability criteria can be applied to the CT component.
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2.7.2. CRITERIA FOR ACCEPTABILITY OF CT SYSTEMS
Table 2.19 Criteria of acceptability for CT Equipment see notes 1-3 Physical Parameter Suspension Level Reference Type Notes Accessible protocols4 Dose ± 20% of should be CTDI, DLP /C , VOL manufacturer's IEC (2004a) A consistent with C , P , W K.L CT specifications; good practice5 ESPECIALLY for paediatrics. Accuracy of indicated Dose ± 20% A dose parameters indicated dose Noise ± 25 % of Image noise IPEM (2005a) B baseline. Value ±8 HU CEC (2006) recommended in Uniformity B IEC (2004a) is ±4 HU CT number ± 20 HU (French (water); ± 30 HU standards are ±4 CT number accuracy (other material) IPEM (2005a) A HU nominal or compared to baseline baseline) values Any artefact likely to impact Artefact D on clinical diagnosis Image Display and See section 2.3 Printing + 0.5 mm for <1 mm ; ±50% for 1 to Image slice width IEC (2004a) A 2 mm; ± 1mm above 2 mm. 1 Protocols either programmed in lookup table or in written form. 2 MPE should compare procedure dose levels with appropriate DRLs 3 applicable for equipment manufactured after 2001
4 Protocols are programmed in lookup table or in written form 5 MPE should compare procedure dose levels with appropriate diagnostic reference levels
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2.8. DUAL ENERGY X-RAY ABSORPTIOMETRY
2.8.1. INTRODUCTION
Dual-energy X-ray Absorptiometry (DXA) is primarily used in determination of bone mineral density; however its application has more recently been extended to include estimates of body fat content. It is performed on equipment specifically designed for and dedicated to these purposes. Similar examinations are performed on CT with much higher doses (Kalender, 1995).
For comparison of scanner results and longitudinal studies the accuracy of calibration is critical. The effect of software updates also needs to be monitored. However there are well documented discrepancies between the results obtained on the scanners of major manufacturers (Kelly, Slovik and Neer, 1989). Further work in this area is essential.
2.8.2. ACCEPTABILITY CRITERIA FOR DXA SYSTEMS
Table 2.20 Criteria of Acceptability for DXA Equipment Physical Parameter Suspension Level Reference Type Notes Patient Entrance Less than 500 μGv for Larkin et al (2008) C Normal from Dose spine examination. Njeh et al (1999) survey is 20 – Sheahan (2005) 200 μGv) Clinical Protocol – Outside +/- 50% standard. deviation from Worst case 35% manufacturers from Larkin paper specified nominal and 40% from patient dose Sheahan paper. Repeatability of See Section 2.2 Exposures BMD accuracy Outside 3% of Larkin et al (2008) C Standard protocol manufacturer‟s Sheahan (2005) with supplier‟s specified BMD BIR (2001) phantom. IAEA (2009) Sheahan et al (2005)
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3. NUCLEAR MEDICINE EQUIPMENT
The technical parts of Sections 2, 3, and 4 assume those reading and using them are familiar with the introduction and have a good working knowledge of the relevant types of equipment and appropriate testing regimes.
3.1. INTRODUCTION
The safe, efficient and efficacious practice of nuclear medicine involves the integration of a number of processes. The quality of each process will have an impact on the overall quality of the clinical procedure and ultimately on the benefit to the patient. It is important, therefore, that each process be conducted within the framework of a quality assurance programme that, if followed, can be shown to achieve the desired objectives with the desired accuracy.
The levels of activity in radiopharmaceuticals to be administered clinically are governed primarily by the need to balance the effectiveness and the safety of the medical procedure by choosing the minimum absorbed dose delivered to the patient to achieve the required objective i.e. diagnostic image quality or therapeutic outcome. To realize this goal, it is important to keep in mind that a nuclear medicine procedure consists of several components, all of which must be controlled in order to have an optimal outcome.
Although the quality assurance of radiopharmaceuticals is an important process (IAEA, 2006), it is not an objective of this section. However, the performance testing of the equipment needed to carry out the quality assurance of radiopharmaceuticals is an objective, both for therapeutic and diagnostic procedures. Devices are included for the determination of administered dose and radiochemical purity such as activity measurement instruments (activity meter or dose calibrator), gamma counter, thin layer chromatography scanner and high performance liquid chromatography radioactivity detector.
More specifically the objective of this section is to specify acceptable performance tolerance levels (suspension levels) for the equipment used in Nuclear Medicine procedures, both for gamma camera and positron emission based procedures. In-vitro Nuclear Medicine
Page 51 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment diagnostic equipment and instruments are not covered since these do not contribute to the patient exposure.
Some Positron Emission Tomography Installations have in-house production of the radiopharmaceuticals they use (e.g. FDG labelled with 18F), utilising either self-shielded cyclotrons or cyclotrons placed in specially designed bunkers. This activity is regarded as a radiopharmaceutical manufacturing activity and therefore is outside the scope of this report.
This section also covers the instruments needed for therapeutic procedures and intra- operative probes, since these are used directly on the patient to trace the administered radioactivity.
When equipment no longer meets the required performance specifications (suspension levels), it should be withdrawn from use, may be disposed of, and replaced (Article 8 (3) of Council Directive 97/43/Euratom). Alternatively, following a documented risk assessment involving the MPE and the Physician, equipment may be used for less demanding tasks for which a lower specification of performance is acceptable. The operator must be advised of the circumstances.
The suspension levels stated are intended to assist in the decision making process regarding the need for recalibration, maintenance or removal from use of the equipment considered.
This section considers equipment used for:
1 Nuclear medicine therapeutic procedures
2 Radiopharmacy quality assurance programme
3 Gamma camera based diagnostic procedures
4 Positron emission diagnostic procedures
5 Hybrid diagnostic systems
6 Intra-operative probes
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Each part of this section is comprised of a brief introduction and a list of relevant equipment. For each piece of equipment, a brief introduction, a table with the critical performance parameters and the suspension levels are given. References to recommended test methods for each parameter are also given.
3.2. NUCLEAR MEDICINE THERAPEUTIC PROCEDURES
3.2.1. INTRODUCTION
Unsealed radioactive sources are administered to patients orally, intravenously or injected into various parts of the body for curative or palliation purposes. The management of the patient depends on the activity and radionuclide used to give the prescribed absorbed dose. It may be necessary for the patient to be confined into a specially designed room for a few days before being released from the hospital to provide radiation protection to hospital staff and members of the public.
When working with unsealed radioactive sources, contamination always presents a potential hazard. Such contamination may come from persons working with the radioactive sources or from patients who have been treated with these substances. Such contamination presents a hazard to anybody coming into contact with it and should be avoided if at all possible, monitored and controlled if it occurs.
The patient undergoing treatment with unsealed radioactive sources must also be checked before he/she is released from hospital to determine that the dose rate from his/her body is down to acceptable levels for members of the public.
Three types of equipment that are used in Nuclear Medicine therapeutic procedures are considered in this part. These are:
Activity measurement instruments
Contamination monitors
Patient dose rate measuring instruments
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3.2.2. ACTIVITY MEASUREMENT INSTRUMENTS
Many different radionuclides are used for Nuclear Medicine therapeutic procedures. The amount of activity to be administered to the patient must be determined accurately. Activity measurement instruments, commonly known as Isotope Calibrators or Dose Calibrators, must be capable of measuring the activity of a particular radionuclide (gamma or beta emitting) accurately over a wide range of energies for correct determination of the patient dose. They must also be capable of measuring accurately over a wide range of activities.
The performance of activity measurement instruments must be assured through a quality assurance programme conforming to international standards (IEC, 1994c; IEC, 2006). The suspension levels are given in Table 3.1 for each critical parameter together with the type of criterion used and a reference to a recommended test method.
Table 3.1 Suspension Levels for Activity Measurement Instruments Physical Parameter Suspension Level Reference Type Background response > 1.5 X Usual IEC (2006) (section 4.1) C Background IEC (1994c) (section 8) Constancy of instrument ± 10% IEC (2006) (section 4.2) C response Instrument Accuracy ± 10% IEC (1994c) (section 3) C Instrument Linearity ± 10% IEC (2006) (section 4.3) C IEC (1994c) (section 4) System reproducibility ± 10% IEC (1994c) (section 5) C Sample volume characteristics ± 15% IEC (1994c) (section 7) C Long-term reproducibility ± 10% IEC (1994c) (section 9) C
The suspension levels given in the above table are for instruments used for the measurement of the activity of gamma emitting sources with energies above 100keV. If these instruments are calibrated to measure low gamma ray energies (below 100 keV), beta or alpha emitting sources (Siegel et al, 2004) and the instrument is suspected of malfunctioning then a test with a relevant source needs to be carried out to confirm the suspicion using the values in the above table.
3.2.3. CONTAMINATION MONITORS
The contamination monitor (also called area survey meter) is designed for the detection and measurement of radioactivity (alpha, beta and gamma) on the surface of objects, clothing, Page 54 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment persons etc. It is used wherever contamination by radioactive substances may be encountered and has to be monitored routinely.
The determination of a monitor‟s (instrument‟s) performance can be at different levels of complexity (ICRU, 1992). A more detailed level is required for the evaluation or type testing of a particular monitor design. Once the monitor has been type tested, less extensive procedures can be used to establish either that a given monitor has maintained its calibration or that it has the same characteristics as the original type tested monitor (IEMA, 2004; IPSM, 1994). The complexity of the procedure depends on what information is required and is generally intermediate between that required by a full type test and a simple reproducibility check.
The suspension levels are given in Table 3.2 for each critical parameter of contamination monitors together with the type of criterion used and the reference to a recommended test method.
Table 3.2 Suspension Levels for Contamination Monitors Physical Parameter Suspension Level Reference Type Sensitivity > 1.2 X Usual Background IEC (2001a) (section 4.2) B Monitor Linearity ± 20% IPSM (1994) (section 3.3) B IEC (2006) (section 4.3) IEC (1994c) (section 4) Statistical Fluctuation of ± 20% IPSM (1994) (section 3.4) B Reading Monitor Response Time ± 10% IPSM (1994) (section 3.5) B Energy Dependence of ± 20% IPSM (1994) (section 3.6) B Monitor
There is a large variation between the different types of contamination monitors. The above suspension levels are a compromise and in some cases may be considered as too conservative.
3.2.4. PATIENT DOSE RATE MEASURING INSTRUMENTS
A patient who has been administered with a therapeutic amount of activity of a radionuclide becomes a radioactive source and may need to be confined in a specially designed room for a few days before being safe to be released from hospital. The monitoring of the patient
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dose rate is very important when gamma radiation is being emitted that can irradiate other persons at a distance from the patient. Therefore, the gamma dose rate of the patient is measured at a standard distance and should be below the acceptable level before the patient is released from hospital.
The performance of a patient dose rate measuring instrument must be assured through a continuous quality assurance programme conforming to international standards (IEMA, 2004) and other commonly acceptable reports (ICRU, 1992; IPSM, 1994). The suspension levels are given in Table 3.3 for each critical parameter.
Table 3.3 Suspension Levels for Patient Dose Rate Measuring Instruments Physical Parameter Suspension Level Reference Type Instrument Dose Rate ± 20% IPSM (1994) (section 3.3) C Linearity IEC (2006) (section 4.3) IEC (1994c) (section 4) Statistical Fluctuation of ± 20% IPSM (1994) (section 3.4) C Reading Instrument Dose Rate ± 10% IPSM (1994) (section 3.5) C Response Time Energy Dependence of ± 20% IPSM (1994) (section 3.6) C Instrument
There is a large variation between the different types of patient dose rate measuring instruments. The above suspension levels are a compromise and in some cases may be considered as too conservative.
3.2.5. RADIOPHARMACY QUALITY ASSURANCE PROGRAMME
The quality of the radiopharmaceutical administered to the patient has to be such that it will not cause adverse effects to the patient, expose the patient to unnecessary radiation and at the same time be specific for the organ of interest. As the injected radiopharmaceutical circulates in the blood system before it is absorbed and preferentially concentrated in the target organ/tissue, other organs/tissues of the body absorb some of the radiopharmaceutical and therefore receive an absorbed dose related to the amount of radiopharmaceutical. Penetrating radiation from the target organ/tissue also irradiate other organs/tissues. Therefore, the maximum amount administered should not exceed the
Page 56 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment recommended local Derived Reference Levels (DRLs). Poor radiochemical purity will also result in radioactivity going to non-target organs and irradiate them unnecessarily.
Also different radiopharmaceuticals are used depending on the imaging modality used (PET or SPECT). Furthermore, for a specific examination there may be more than one radiopharmaceutical that can be used to acquire the final image.
Taking the above into consideration the administered activity to the patient must be prepared in a specially designed room, the radiopharmacy (also called the Hot Laboratory), under a strictly controlled written procedure. The performance of the instruments used in the preparation must be assured under a quality control programme.
The type and number of instruments required in a radiopharmacy will depend on the number of modalities available in a Nuclear Medicine Department and the variety of radiopharmaceuticals and procedures used. For simplicity these are divided into two categories:
1. Radiopharmacy for gamma camera based diagnostic procedures
2. Radiopharmacy for positron emission based diagnostic procedures
In cases were both gamma camera based and positron emission modalities are available, the radiopharmacy will need to have instruments capable for accommodating both types of radiopharmaceuticals, either in a single instrument or different instruments for each type.
3.3. RADIOPHARMACY FOR GAMMA CAMERA BASED DIAGNOSTIC PROCEDURES
3.3.1. INTRODUCTION
The objective of this part is to define suspension levels for the performance parameters of the equipment needed to carry out the quality assurance programme for radiopharmaceuticals used with gamma camera based modalities. These include devices used for radiochemical purity determination such as the activity measurement instrument, the gamma counter and the thin layer chromatography scanner.
The availability of the above equipment in a radiopharmacy depends on the level and sophistication of its activities. Page 57 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
For the protection of the personnel working in a radiopharmacy, instruments such as contamination monitors are also essential. Therefore this part considers the following instruments:
Activity Measurement Instruments
Gamma Counters
Thin Layer Chromatography Scanners
Contamination Monitors
3.3.2. ACTIVITY MEASUREMENT INSTRUMENTS
The activity measurement instruments that are used for gamma camera based diagnostic procedures need to cover the energy range and activity range of the radiopharmaceuticals that are used in the particular department. The quality assurance programme that must be followed to assure their performance, as well as the suspension levels are the same as those described in section 3.2.2, under “Activity measurement instruments”.
3.3.3. GAMMA COUNTERS
These are single “well type” gamma counters used in the radiopharmacy to measure the activity (number of counts per second) on the paper chromatography strips used for the radiochemical purity testing of radiopharmaceuticals. These are similar to gamma counters for in-vitro diagnostic investigations and are used to compare the number of counts of the different sections of the paper chromatography strips.
The performance of a gamma counter must be assured through a continuous quality assurance programme conforming to international standards (IEC, 2009) and other commonly accepted reports (ICRU, 1992; IPSM, 1994). The suspension levels are given in Table 3.4 for each critical parameter of a well type gamma counter.
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Table 3.4 Suspension Levels for Well Type Gamma Counters Physical Parameter Suspension Level Reference Type Sensitivity > 1.5 X Usual IEC (2001a) (section 4.2) C Background Instrument Dose Rate ± 20% IPSM (1994) (section 3.3) C Linearity IEC (2006) (section 4.3) IEC (1994c) (section 4) Statistical Fluctuation of ± 20% IPSM (1994) (section 3.4) C Reading Instrument Dose Rate ± 10% IPSM (1994) (section 3.5) C Response Time Energy Dependence of ± 20% IPSM (1994) (section 3.6) C Instrument Sample Volume ± 15% IEC (1994c) (section 7) C Characteristics
The above suspension levels are a compromise and in some cases may be considered as too conservative.
Test methods that can be used to monitor a gamma counter are similar to those of patient dose rate measuring instruments. The test method for sensitivity is similar to that of contamination monitors. The test method for volume dependence of the well type gamma counters is similar to that of the activity measurement instruments.
3.3.4. THIN LAYER CHROMATOGRAPHY SCANNERS
A thin layer chromatography scanner is a gamma counter that simultaneously measures or scans the length of the paper chromatography strip and calculates automatically the count ratio as a measure of radiochemical purity.
The suspension levels of each critical parameter of a thin layer chromatography scanner are similar to those of a gamma counter (Table 3.4).
3.3.5. CONTAMINATION MONITORS
The contamination monitors usually encountered in a radiopharmacy take the form of continuous room monitors for air borne contamination and for the contamination of hands and clothes of the personnel working in the radiopharmacy. The quality assurance
Page 59 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment programme that must be followed to assure their performance is the same as that described for contamination monitors (see section 3.2.3).
3.4. RADIOPHARMACY FOR POSITRON EMISSION BASED DIAGNOSTIC PROCEDURES
The specific radioactivity of the radiopharmaceutical is an important factor to consider in guaranteeing the quality of a PET study (Nakao et al, 2006). Chemical impurities in radiopharmaceuticals, such as precursors and analogues contained in the preparation, may interfere with the PET study (and may cause adverse reactions in the patient). Therefore it is necessary to measure the specific activity and chemical impurities accurately before administration.
Due to the very short half-lives of PET radionuclides, quality control is carried out by their producer and they are delivered to the hospital ready for patient administration.
The instruments usually found in a hospital PET radiopharmacy are the same as those for gamma camera based diagnostic procedure radiopharmacy (Section 3.3.1), calibrated for the specific PET radionuclides used in a particular hospital. Additionally, in hospital research departments, one may find instruments such as High Performance Liquid Chromatography (HPLC), Gas Chromatography (GC) and Thin Layer Chromatography (TLC) that are used to verify the specific activity, the radiochemical and chemical purity of the radiopharmaceutical used (Dietzel, 2003). There are also all-in-one instrument that perform these analyses at the same time. These analysers need to meet Good Manufacturing Practice (GMP) and Good Laboratory Practice (GLP) regulation criteria (OECD, FDA) (Dietzel, 2003).
Currently there are no commonly acceptable suspension levels for such instruments and therefore the manufacturer‟s recommendations for each specific instrument should be used.
3.3 GAMMA CAMERA BASED DIAGNOSTIC PROCEDURES
3.3.1 INTRODUCTION
The gamma camera is currently available in a number of configurations capable not only of performing simple Planar Imaging (Section 3.4.2) but also of Whole Body Imaging (Section Page 60 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
3.4.3) and Single Photon Emission Computed Tomography (SPECT) (Section 3.4.4). Some dual headed Gamma Cameras with appropriate coincidence circuits and software are also capable of performing Positron Emission Tomography (Section 3.4.5). However, the PET Scanner dealt with in section 3.5 is rapidly replacing such systems.
The IEC (IEC, 2005c; IEC, 2004b, 1998b, c) and the National Electrical Manufacturers Association (NEMA) (NEMA, 2007a, b) in the USA have published relevant standards. These are almost identical with respect to many test procedures, test objects and radioactive sources and have been used extensively. The IEC and NEMA standards were aimed primarily at manufacturers but are now more orientated towards user application than previous publications making it easier to test for compliance in the field. The NEMA Standard also includes directions for the testing of Gamma Cameras with discrete Pixel Detectors. In this section the suspension levels are mainly related to manufacturer‟s specifications, Type A Criteria. The NEMA standards require that the system “meet or exceed” the manufacturer‟s specification unless the specification is considered “typical performance”. “Typical” specifications are used when the measurement is sufficiently time- consuming that measuring large numbers of units is difficult. For these tests greater suspension levels have been proposed.
In addition to the standards, there are a number of publications on quality control that provide a wealth of useful background material and detailed accounts of test methods and phantoms for routine assessment which must be undertaken on a regular basis according to national protocols (IPEM, 2003b; AAPM, 1995).
3.4.1. PLANAR GAMMA CAMERA
Gamma cameras are normally operated with collimators appropriate to the study being performed. Tests performed with collimators in situ are termed „system‟ tests. Tests performed without collimators are „intrinsic‟ tests. Since there is a large range of different types of collimator in use and their characteristics vary from type to type and from manufacturer to manufacturer, professional judgement may have to be called on with respect to system tests for a particular collimator. It is important to perform system non- uniformity tests on all collimators in clinical use in order to detect collimator damage at the earliest opportunity (IEC, 2005b)
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Table 3.5 Suspension Levels for Planar Gamma Systems Physical Parameter Suspension Level Reference Type Intrinsic Spatial >1.05 times the IEC (2005a), Section 4.5 A Resolution manufacturer‟s NEMA (2007a), Sections 2.1 and 2.7 specification Intrinsic Spatial Non- >1.05 times the IEC (2005a), Section 4.4 A Linearity manufacturer‟s NEMA (2007a) Sections 2.2 and 2.7 specification Intrinsic Non-uniformity >1.05 times the IEC (2005a), Section 4.3 A manufacturer‟s NEMA (2007a), Sections 2.4 and 2.8 specification Intrinsic energy >1.05 times the IEC (2005a), Section 4.6 A resolution manufacturer‟s NEMA (2007a), Section 2.3 specification Multiple window spatial >1.05 times the IEC (2005a), Section 2.5 A registration manufacturer‟s NEMA (2007a), Section 4.7 specification Intrinsic count rate <0.9 times the NEMA (2007a), Section 2.6 A performance in air manufacturer‟s specification System Spatial >1.05 times the IEC (2005a), Section 4.3 A Resolution with scatter manufacturer‟s NEMA (2007a), Section 3.2 specification System Non-uniformity >1.05 times the IEC (2005a), Section 4.5 A manufacturer‟s specification
3.4.2. WHOLE BODY IMAGING SYSTEM
The IEC 61675-3 standard (IEC, 1998c) and the NEMA Standard NU-1 (NEMA, 2007a) contain a limited number of tests for Whole Body Systems. Before performing these specific tests, it is advisable that the basic tests for the Planar Gamma Camera are performed for each detector head used for whole body imaging (Table 3.5).
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Table 3.6 Suspension Levels for Whole Body Imaging Systems Physical Parameter Suspension Level Reference Type Whole body non- >10% difference between this IPEM (2003b) Section 4.2.1 B uniformity and planar system uniformity Whole Body Spatial >1.05 times the IEC (1998c), Section 3.2 A Resolution Without manufacturer‟s specification NEMA (2007a), Section 5.1 Scatter Scanning constancy Any deviation in mean count IEC (1998c), Section 3.1 A rate greater than expected from Poisson statistics
3.4.3. SPECT SYSTEM
The IEC 61675-3 standard (IEC, 1998c) and the NEMA Standard NU-1 (NEMA, 2007a) both contain a section devoted to SPECT systems. The basic tests for Planar Gamma Camera systems should be performed on each detector head used for SPECT before commencing with the tests specific for SPECT.
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Table 3.7 Suspension Levels for SPECT Systems Physical Parameter Suspension Level Reference Type Centre of Rotation COR X axis offset: IEC (2004d), (1998b), Sections 3.1.1 A (COR) and Detector >1.05 times the and 3.1.2 Head Tilt manufacturer‟s NEMA (2007a), Section 4.1 specification IAEA (2007c) Section 4.3.3 For Multiple head IPEM (2003b) Section 5.3.2 systems offsets >5% Mismatch Y axis >5% between detectors Collimator Hole >1.05 times the IEC (2004d), (1998b), Section 3.2 A Misalignment manufacturer‟s IAEA (2007c), Section 3.3.6 specification IPEM (2003b) Section 5.3.3 SPECT System Spatial >1.05 times the IEC (2004d), (1998b), Section 3.6 A Resolution manufacturer‟s NEMA (2007a), Section 4.3 specification Detector to Detector >1.1 times the NEMA (2007a), Section 4.5 A Sensitivity Variation manufacturer‟s specification Variation of Response ≥1.5% AAPM (1995), Section III.A.1 A with Detector Rotation IPEM (2003b) Section 5.3.7
3.4.4. GAMMA CAMERAS USED FOR COINCIDENCE IMAGING
The basic tests for Planar Gamma Camera Systems should be performed on each detector (Table 3.5). However, the thicker crystals required for these cameras do not perform as well with respect to intrinsic spatial resolution as the thinner crystals intended mainly for use with technetium-99m based radiopharmaceuticals (Table 3.8). Tolerances for the other tests are the same as those in Table 3.6.
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Table 3.8 Suspension Levels for Coincidence Gamma Camera Systems Physical Parameter Suspension Level Reference Type Intrinsic Spatial >1.05 times the IEC (2005a), Section 4.5 A Resolution manufacturer‟s NEMA (2007a), Sections 2.1 and 2.7 specification [A] System Spatial >1.05 times the IEC (2005a), Section 4.3 A Resolution manufacturer‟s NEMA (2007), Section 3.2 specification [A]
3.5. POSITRON EMISSION DIAGNOSTIC PROCEDURES
3.5.1. INTRODUCTION
Positron Emission Tomography (PET) is a nuclear medicine imaging technique that utilises positron-emitting radionuclides, normally produced in a cyclotron. The most frequent clinical indication for a PET scan today is in the diagnosis, staging, and monitoring of malignant tumours. Other indications include assessment of neurological and cardiological disorders.
The PET technology has evolved rapidly in the past decade. Two significant advances have greatly improved the accuracy of PET imaging:
(i) the introduction of faster scintillation crystals and electronics which permit higher data acquisition rates, and,
(ii) the combination, in a single unit, of PET and CT scanners (“hybrid” scanners, see section 3.6).
It is expected that the utilisation of PET will increase dramatically in the future. In some cases it may substitute for current nuclear medicine investigations but, in general, PET will be complementary to the use of single photon imaging with the gamma camera.
The purpose of this section is to specify Suspension levels for PET scanners to be used in clinical imaging. Note that these technical requirements relate to clinical facilities and are not intended to apply to research installations.
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3.5.2. POSITRON EMISSION TOMOGRAPHY SYSTEM
PET is based on the coincidence detection of two oppositely directed 511 keV photons emitted from the annihilation of a positron with an atomic electron in vivo. The detection of such events, known as true coincidences, is used for the reconstruction of an image describing the in vivo distribution of a positron emitting radiopharmaceutical. Apart from these events, there are also other types of erroneous coincidences that may be detected, namely scattered and random coincidences. Scattered coincidences are events formed by detection of two annihilation photons, where at least one has undergone Compton scattering before detection (but still are detected in the energy window), while random coincidences are formed when two photons originating from two different annihilation sites are detected within the system‟s coincidence time window.
The performance of PET systems must be assured through a continuous quality assurance programme conforming to international standards (IEC, 2008c; NEMA, 2007b; IEC, 2005) and other commonly accepted reports (IAEA, 2009). The suspension levels are based on Type A Criteria. These are given in Table 3.9 for each critical parameter of PET systems.
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Table 3.9 Suspension Levels for PET Systems Physical Parameter Suspension Level Reference Type
Spatial Resolution FWHMobserved NEMA (2007b) (section 3.3) A
>1.05*FWHMexpected Sensitivity NEMA (2007b) (section 5.3) A
STOT observed < 0.95*STOT expected IEC (2008d) (section 3.3) IEC (2005b) (section 4.2)
Energy resolution REobserved > 1.05*REexpected IAEA (2007c) (section A 4.1.4)
Scatter fraction, count NECobserved
Uniformity %NUobserved > NEMA (2007b) (section 7.3) A
1.05*%NUexpected Image quality and Unacceptable visual IAEA (2007c) (section A accuracy of attenuation assessment 5.1.4) and scatter correction
Coincidence timing RTobserved > 1.05*RTexpected IAEA (2007c) (section A resolution (TOF) 4.1.6) Mechanical Tests If any mechanical part is C found to compromise the safety of operation * Expected and recommended values are the values for each parameter measured or agreed during the acceptance testing. FWHM = Full Width at Half Maximum
3.5.3. HYBRID DIAGNOSTIC SYSTEMS
A hybrid diagnostic system is defined as the combination of two diagnostic modalities into one system. Examples of such systems are PET-CT, SPECT-CT, PET-MRI, etc. Usually one modality presents functional (molecular) images and the other anatomic images. The fusion (combination) of their images gives a higher diagnostic value than the individual images alone.
The quality control procedures of each individual modality comprising the hybrid system are well established and if followed as recommended, the hybrid system will operate optimally. The suspension levels for the individual modalities are valid for the hybrid systems as well. The only concern with hybrid systems even today, is the alignment of the imaging modalities of the hybrid system. Here it is recommended that an independent alignment
Page 67 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment test, using a phantom in the place of a patient, be used at regular intervals to assure the alignment of the modalities comprising the hybrid system (NEMA, 2007b; Nookala, 2001).
The suspension level is based on Type C Criteria and is given in Table 3.10 for the alignment of a hybrid system.
Table 3.10 Suspension Level for the Alignment of Hybrid Systems Physical Parameter Suspension Level Reference Type Alignment Test of a > ± 1 pixel or ± 1 Nookala (2001) C Hybrid System mm, whichever is bigger
3.4 INTRA-OPERATIVE PROBES
Radiotracer techniques using intra-operative gamma probes are procedures that surgeons can use to more easily localise small tumours or lymph nodes to be removed in a surgical procedure. Use of intra-operative probes decreases operating time, decreases patient morbidity and improves staging accuracy. All of these can lead to improved treatment, improved quality of life and higher long-term survival rates (Halkar and Aarsvold, 1999).
The most established type of intra-operative probe is the non-imaging gamma probe. Other types such as imaging intra-operative probes and beta probes are less well established or are still under development and therefore their performance parameters are less rigorously defined. Furthermore a wide range of gamma probe systems are commercially available with different detector material, detector sizes and collimator abilities. Various methods of evaluation of such equipment have been proposed (NEMA, 2004; IEC, 2001a). For these reasons suspension levels to cover all the types of intra-operative probes do not exist.
For the most common application, that of the detection of the sentinel lymph node (SLN), minimum requirements of a gamma probe system has been recommended (Wengenmair and Kopp, 2005; Yu et al, 2005). These were derived mainly from comparison studies of commercially available probe systems and are presented in Table 3.11. It is recommended that the user of a particular probe system establish a quality assurance system for the probe system in use and establish suspension levels taking into account the manufacturer‟s recommendations.
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Table 3.11 Suspension Levels for a SLN intra-operative gamma probe system Physical Suspension Level Reference Type Parameter Radial Sensitivity FWHM > 40o Wengenmair and Kopp (2005) C (far field) NEMA (2004) (section 3.9) Spatial Resolution FWHM >15mm for Wengenmair and Kopp (2005) C lymph nodes in head, NEMA (2004) (section 3.5) neck and supraclavicular region FWHM > 20mm for lymph nodes in extremities, axilla and groin Sensitivity < 5.5 cps/kBq Wengenmair and Kopp (2005) C NEMA (2004) (section 3.1 – 3.4) Shielding > 0,1 of minimum Wengenmair and Kopp (2005) C system sensitivity
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4 RADIOTHERAPY
The technical parts of Sections 2, 3, and 4 assume those reading and using them are familiar with the introduction and have a good working knowledge of the relevant types of equipment and appropriate testing regimes.
3.6. INTRODUCTION
The purpose of this document is to list performance parameters and their tolerances. Specific reference is not made to safety requirements, but these need to be checked at acceptance and after maintenance and upgrades and may result in suspension of the equipment during operation, if not met.
These functional performance tolerances reflect the need for precision in radiotherapy and the knowledge of what can be reliably achieved with radiotherapy equipment. The tolerances presented must be used as suspension levels at which investigation must be initiated, according to the definition in section 1.4.2. Where possible, it will be necessary to adjust the equipment to bring the performance back within tolerance limits. If adjustment is not possible, e.g. loss of isocentric accuracy, it may still be justified to use the equipment clinically for less demanding treatments. Such a decision can only be taken after careful consideration by the clinical team (responsible medical physics expert and radiation oncologist) and must be documented as part of an agreed hospital policy. Alternatively it should be suspended from use until performance is restored. Suspension from use can also be required if the safety requirements in the relevant safety standards are not met.
In the following clauses these levels are referred to as performance tolerance levels, as this is the terminology used in the quoted IEC standards. However, in the tables these levels are listed as tolerance/suspension levels as they correspond also with the definition of suspension level in section 1.4.2 and used in the other sections of this document.
The performance tolerance/suspension levels quoted in this section have been extracted mostly from international and national standards (category type A), supplemented by guidance from national professional bodies (category type B) (see section 1.4.3). Tolerances are expressed in the same format (e.g. ± or maximum deviation) as originally given in the quoted standards and guidance documents. Page 70 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
All test equipment used in measuring functional performance must be well maintained, regularly calibrated and traceable (where appropriate) to national standard laboratories.
3.3 LINEAR ACCELERATORS
IEC 60601-2-1 (1998a) is the standard which identifies those features of design that are regarded as essential for the safe operation of the equipment and places limits on the degradation on the performance beyond which a fault condition exists. These include protection against electrical and mechanical hazards and unwanted and excessive radiation hazards (i.e. dose monitoring systems, selection and display of treatment related parameters, leakage radiation and stray radiation).
IEC 60976 (2007) and IEC 60977 (2008c) are closely related to this standard. The former specifies test methods and reporting formats for performance tests of medical electron accelerators for use in radiotherapy, with the aim of providing uniform methods of doing so. The latter is not a standard per se but suggests performance values, measured by the methods specified in IEC 60976 (2007) that are achievable with present technology.
The values given in Table 4.1 are a summary of the tolerance values in IEC 60977 (2008c) and are based on the methodology in IEC 60976 (2007). These values are broadly consistent with the tolerances previously specified in IPEM 81 (1999), AAPM Report 46 (1994) and CAPCA standards (2005a). For a detailed description of test methods and conditions, please refer to the IEC and IPEM documents. A list of suggested test equipment is included in IEC 60977 (2008c). The table is intended to include the performance parameters of all treatment devices incorporating a linear accelerator. All tests form part of acceptance testing. Where tests are performed routinely for quality control, suggested frequencies of testing are given in IEC 60977 (2008c), IPEM 81 (1999), AAPM Report 46 (1994), CAPCA standards (2005a) and other national QA protocols.
In the table, “IEC” refers to IEC 60976 (2007) and 60977 (2008c) and the numbers in the Reference column refer to the clauses in these publications. “IPEM (1999)” refers to tables in its section 5.2.
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Table 4.1 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of a medical electron accelerator Physical Parameter Tolerance/ Reference Type Suspension (IEC (2007, Level 2008c) unless stated) Uniformity of radiation fields 9 X-ray beams Beam flatness in flattened area 1.06 A (max/min ratio) (see also IEC) Beam symmetry (max/min ratio) 1.03 A Dependence on gantry and collimator See IEC A angle
Beam flatness at dmax See IEC A Wedge fields Maximum deviation of wedge 2 % IPEM (1999) B factor Maximum deviation of wedge 3 % IPEM (1999) B factor with gantry angle Maximum deviation of wedge 2° A angle IMRT See IEC A Electron beams Beam flatness See IEC A Dependence of flatness on gantry 3 % A and collimator angle Beam symmetry (max/min ratio) 1.05 A Maximum surface dose (max/min 1.09 See IEC A ratio) Dose monitoring system 7 Calibration check 2 % A Reproducibility 0.5 % Proportionality 2 % IPEM (1999) 1% A, B Dependence on angular position 2 % IPEM (1999) B Dependence on gantry rotation 2 % A Stability of calibration within day 2 % A Stability in moving beam radiotherapy See IEC A Depth dose characteristics See IEC 8 A X-ray beams Penetrative quality 2 % IPEM (1999) B Depth dose and profile 2 % IPEM (1999) B Electron beams A
Minimum depth of dmax 1 mm A Practical range to 80% ratio 1.6 A Penetrative quality 3 % or 2 mm A Page 72 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
Maximum relative surface dose 100 % A Stability of penetrative quality 1 % or 2 mm Indication of radiation fields 10 X-ray beams A Numerical field indication 3 mm or 1.5 % A See also IEC For MLCs 3 mm or 1.5 % A See IEC Light field indication 2 mm or 1 % A See also IEC Centres of radiation field and 2 mm or 1 % A light field See also IEC For MLCs 2 mm or 1 % A See also IEC For SRS/SRT 0.5 mm A See also IEC Reproducibility 2 mm SRS alignments 0.5 mm See also IPEM A, B See IEC (1999) Electron beams Light field indication 2 mm A Collimator geometry Parallelism of opposing edges 0.5° A Orthogonality of adjacent edges 0.5° A Beam centring with beam limiting 2 mm A system rotation Light field Field size (10*10 cm2) 2 mm IPEM (1999) B Illuminance (minimum) 25 lux A Edge contrast ratio (minimum) 4.0 A Indication of the radiation beam axis 11 On entry X-rays 2 mm A Electrons 4 mm A SRS 0.5 mm A On exit X-rays 3 mm A SRS 0.5 mm A Isocentre 12 Radiation beam axis 2 mm IPEM (1999) 1 A, B mm Mechanical isocentre 1 mm IPEM (1999) B Indication 2 mm SRS 0.5 mm IPEM (1999) B Distance indication 13 Isocentric equipment 2 mm IPEM (1999) A, B Page 73 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
3mm Non-isocentric equipment 5 mm A Zero position of rotational scales 14 Gantry rotation 0.5° IPEM (1999) B Roll and pitch of radiation head 0.1° A Rotation of beam limiting system 0.5° IPEM (1999) B Isocentric rotation of the patient support 0.5° A Table top rotation, pitch and roll 0.5° A Accuracy of rotation scales 1° IPEM (1999) B Congruence of opposed radiation fields 1 mm 15 Movements of patient support 16 Vertical movements 2 mm A Longitudinal and lateral movements 2 mm IPEM (1999) B Isocentric rotation axis 1 mm A Parallelism of rotational axes 0.5° A Longitudinal rigidity 5 mm A Lateral rigidity 0.5° and 5 mm A Electronic imaging devices 17 Minimum detector frame time 0.5 s A Corresponding maximum frame rate 2 / s A Minimum signal-to-noise ratio 50 A Maximum imager lag Second to first frame 5 % A Or fifth to first frame 0.3 % A Minimum spatial resolution 0.6 lp/mm IPEM (1999) B
Detachable devices can be attached to either the treatment head or the couch. The former include shadow trays and micro-MLCs, and the latter include devices such as stereotactic frames, head shells, bite-blocks, etc. Where reproducible immobilisation and positioning of the patient is required, the positional tolerance of these devices should be 2 mm in general use and 0.5 mm for SRS.
3.7. SIMULATORS
IEC 60601-2-29 (2008b) is the standard which identifies those features of design that are regarded as essential for the safe operation of the equipment and places limits on the degradation on the performance beyond which a fault condition exists. These include protection against electrical and mechanical hazards and unwanted and excessive radiation hazards. In a similar way to IEC 60976 (2007) and 60977 (2008c) for linear accelerators, IEC 61168 (1993a) and IEC 61170 (1993b) specify test methods and functional
Page 74 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment performance values for radiotherapy simulators. The functional performance requirements of radiotherapy simulators are directly related to the radiotherapy equipment being simulated. The performance tolerances must therefore be at least equal to those considered appropriate for the radiotherapy equipment and in many instances must be better in order not to add to the total positioning errors. There are some differences from recommendations published by national physicists‟ associations (IPEM (1999), AAPM (1994) and CAPCA standards (2005b). Where recommendations from these bodies are adopted they are indicated in the table
The values given in Table 4.2 are a summary of the tolerance values in IEC 61170 (1993b) and are based on the methodology in IEC 61168 (1993a). Where additional tolerances (e.g. for MLC and SRS/SRT simulation) have been suggested in the more recent linear accelerator standards IEC 60976 (2007) and 60977 (2008c) and IPEM (1999), these are indicated in the table. For a detailed description of test methods and conditions, please refer to the IEC and IPEM documents.
All tests form part of acceptance testing. Where tests are performed routinely for quality control, suggested frequencies of testing are given in IEC 61170 (1993b), IPEM (1999), AAPM (1994), CAPCA (2005b) standards and other national QA protocols.
In the table, “IEC” refers to IEC 61168 (1993a) and 61170 (1993b).
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Table 4.2 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of a radiotherapy simulator Physical Parameter Tolerance/ Reference Type Suspension (IEC (1993a,b) Level unless stated) Indication of radiation fields Numerical field indication 2 mm or 1.0 % IPEM (1999) A, B See also IEC For MLCs 2 mm or 1.0 % IEC (2008c, A 2007) Light field indication 1 mm or 0.5 % A See also IEC Centres of radiation field and light 1 mm or 0.5 % IPEM (1999) A, B field See also IEC For MLCs 1 mm or 0.5 % IEC (2008c, A 2007) For SRS/SRT 0.5 mm IEC (2008c, A 2007) Reproducibility 1 mm A SRS alignments 0.5 mm IEC (2008c, A, B 2007) IPEM (1999) Delineator geometry Parallelism of opposing edges 0.5° A Orthogonality of adjacent edges 0.5° A Beam centring with beam limiting 2 mm IEC (2008c, A system rotation 2007) Light field Field size (10*10 cm2) 1 mm A Minimum illuminance 50 lux A Minimum edge contrast ratio 4.0 A Indication of the radiation beam axis On entry 1 mm IPEM (1999) B SRS 0.5 mm IEC (2008c, A 2007) On exit 2 mm A SRS 0.5 mm IEC (2008c, A 2007) Isocentre Radiation beam axis 1 mm IPEM (1999) A, B See also IEC Mechanical isocentre 1 mm IPEM (1999) B Indication 1 mm IPEM (1999) B SRS 0.5 mm IPEM (1999) B Distance indication From isocentre 1 mm A Page 76 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
From radiation source 2 mm A Image receptor to isocentre 2 mm A Zero position of rotational scales Gantry rotation 0.5° IPEM (1999) B Roll and pitch of radiation head 0.1° IEC (2008c) A Rotation of delineator 0.5° IPEM (1999) B Isocentric rotation of the patient support 0.5° IEC (2008c) A Table top rotation, pitch and roll 0.5° IEC(2008c) A Accuracy of rotation scales 1° IPEM (1999) B Congruence of opposed radiation fields 1 mm Movements of patient support Vertical movements 2 mm A Longitudinal and lateral movements 2 mm IPEM (1999) B Isocentric rotation axis 1 mm A Parallelism of rotational axes 0.5° A Longitudinal rigidity 5 mm A Lateral rigidity 0.5° and 5 mm A Electronic imaging devices Minimum detector frame time 0.5 s IEC (2008c, A 2007) Corresponding maximum frame rate 2 / s IEC (2008c, A 2007) Minimum signal-to-noise ratio 50 IEC (2008c, A 2007) Maximum imager lag Second to first frame 5 % IEC (2008c, A 2007) Or fifth to first frame 0.3 % IEC (2008c, A 2007) Minimum spatial resolution 0.6 lp/mm IPEM (1999) B 10.2.6 Radiographic QC Alignment of broad and fine foci images 0.5 mm IPEM (1999) B Fluoroscopic QC Full radiographic and fluoroscopic tests IPEM (1999) B Alignment of Shadow Trays 1 mm IPEM (1999) B
3.8. CT SIMULATORS
CT simulators usually comprise a wide bore CT scanner, together with an external patient positioning and marking mechanism using projected laser lines to indicate the treatment isocentre. This is often termed “virtual simulation”. Since this is an application of CT scanning, there is no international standard. However quality assurance of the scanner and Page 77 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment alignment system is essential to ensure that the isocentre is accurately located in the treatment volume for subsequent treatment planning and treatment. The established standards for CT scanners (see section 2.7) for good image quality and optimum patient radiation dose apply. Acceptable quality assurance regimes are therefore based upon good clinical practice. The most recent work is “Quality assurance for computed-tomography simulators and the computed-tomography-simulation process”: (AAPM, 2003). The tolerance limits in this report are designed to satisfy the accuracy requirements for conformal radiotherapy and have been shown to be achievable in a routine clinical setting. Further guidance is contained in IPEM Report 81 published in 1999. The guidance in Table 4.3 is based on these two reports. IPEM Report 81 suggests that the tests are done under the same scanning conditions as those used clinically. Checks on image quality should also be done after software upgrades in case they affect the calibration of the Hounsfield Units. All tests form part of acceptance testing. Where tests are performed routinely for quality control, suggested frequencies of testing are given in AAPM Report 83 (2003), IPEM (1999), CAPCA (2007b) standards and other national QA protocols.
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Table 4.3 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of CT simulators Physical Parameter Tolerance/ Reference Type Suspension (AAPM,2003) Level unless stated) Alignment of CT Gantry Lasers
With centre of the imaging plane ± 2 mm B
Parallel & orthogonal over length of laser ± 2 mm B projection
Alignment of Wall Lasers
Distance to scan plane ± 2 mm B
With imaging plane over length of laser ± 2 mm IPEM (1999) 1° B projection
Alignment of Ceiling Laser
Orthogonal with imaging plane ± 2 mm B
Orientation of Scanner Table Top
Orthogonal to imaging plane ± 2 mm B
Scales and Movements
Readout of longitudinal position of table ± 1 mm IPEM (1999) 1 mm B top
Table top indexing under scanner control ± 1 mm B
Readout of gantry tilt accuracy ± 1° B
Gantry tilt position accuracy ± 1° B
Scan Position
Scan position from pilot images ± 1 mm IPEM (1999) 1 mm B
Image Quality
Left & right registration None IPEM (1999) B
Image scaling 2 mm IPEM (1999) B
CT number/electron density verification ± 5 HU water B
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± 10 HU air ± 20 HU lung, bone
3.9. COBALT-60 UNITS
IEC 60601-2-11 (2004b) is the standard which identifies those features of design that are regarded as essential for the safe operation of the equipment and places limits on the degradation on the performance beyond which a fault condition exists. These include protection against electrical and mechanical hazards and unwanted and excessive radiation hazards (i.e. controlling timer, selection and display of treatment related parameters, leakage radiation and stray radiation). IEC 60601-2-11 (2004b) also includes requirements for multi-source stereotactic radiotherapy equipment.
The IEC has not published performance tolerances for cobalt-60 units. The functional performance characteristics and tolerance values in Table 4.4 are based on those for linear accelerators in IEC 60976/7 (2008c, 2007) with some changes for cobalt-60 units. The table does not address multi-source stereotactic radiotherapy equipment. There are some differences from recommendations published by national physicists‟ associations (IPEM (1999), AAPM (1994) and CAPCA (2006a) standards). Where recommendations from these bodies are adopted, they are indicated in the table. For a detailed description of test methods and conditions, please refer to the documents indicated.
All tests form part of acceptance testing. Where tests are performed routinely for quality control, suggested frequencies of testing are given in IPEM (1999), AAPM (1994), CAPCA (2006a) standards and other national QA protocols.
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Table 4.4 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of cobalt-60 units Physical Parameter Tolerance/ Reference Type Suspension Level (IEC (2008c) unless stated) Uniformity of radiation fields Beam flatness ± 3 % A Beam symmetry ± 2 % IPEM (1999) B Dependence on gantry and collimator See IEC 60976/7 A angle Wedge fields Maximum deviation of wedge 2 % IPEM (1999) B factor Maximum deviation of wedge 2° A angle Source position (when applicable) 3 mm AAPM (1994) B Controlling Timer and Output Checks Timer check on dual timer difference 1 s IPEM (1999) B Calibration check 2 % A Reproducibility 0.5 % A Proportionality 2 % A Dependence on gantry rotation 1 % IPEM (1999) B Stability in moving beam radiotherapy See IEC 60976/7 IEC 2007, 2008C, Timer linearity 1 % AAPM (1994) B Stability of timer ± 0.01 min A Output vs field size 2 % IPEM (1999) B AAPM (1994) Shutter correction 2 % IPEM (1999) B Depth dose characteristics Penetrative quality 1 % IPEM (1999) B Depth dose and profile 2 % IPEM (1999) B Indication of radiation fields Numerical field indication 3 mm or 1.5 % IPEM (1999) 2 mm A, B Light field indication 2 mm or 1 % Centres of radiation field and light field 2 mm or 1 % AAPM (1994) 3 A, B mm Reproducibility 2 mm A Collimator geometry Parallelism of opposing edges 0.5° A Orthogonality of adjacent edges 0.5° A Beam centring with beam 2 mm A limiting system rotation Light field Field size (10*10 cm2) 2 mm IPEM (1999) B
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Minimum illuminance 25 lux A
Minimum edge contrast ratio 4.0 A Indication of the radiation beam axis On entry 2 mm A On exit 3 mm A Isocentre Radiation beam axis 2 mm IPEM (1999) 1 mm A, B AAPM (1994) 2 mm Mechanical isocentre 1 mm IPEM (1999) B Indication 2 mm A Distance indication Isocentric equipment 2 mm IPEM (1999) 3 mm A, B AAPM (1994) 2 mm Non-isocentric equipment 5 mm A Zero position of rotational scales Gantry rotation 0.5° IPEM (1999) B Roll and pitch of radiation head 0.1° A Rotation of beam limiting system 0.5° IPEM (1999) B Isocentric rotation of the patient support 0.5° A Table top rotation, pitch and roll 0.5° A Accuracy of rotation scales 1° IPEM (1999) B Congruence of opposed radiation 1 mm A fields Movements of patient support Vertical movements 2 mm A Longitudinal and lateral movements 2 mm IPEM (1999) B Isocentric rotation axis 1 mm A Parallelism of rotational axes 0.5° A Longitudinal rigidity 5 mm A Lateral rigidity 0.5° and 5 mm A
3.10. KILOVOLTAGE UNITS
IEC 60601-2-8 (1997a) is the standard which identifies those features of design that are regarded as essential for the safe operation of the equipment and places limits on the degradation on the performance beyond which a fault condition exists. These include protection against electrical and mechanical hazards and unwanted and excessive radiation hazards. Tests are based upon IPEM Report 81 (1999), which is based on a survey of UK practice in 1991. Where recommendations from other bodies are adopted, they are
Page 82 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment indicated in the table. For a detailed description of test methods and conditions, please refer to the IPEM (1999) and CAPCA (2005d) documents.
All tests form part of acceptance testing. Where tests are performed routinely for quality control, suggested frequencies of testing are given in IPEM (1999) and the CAPCA (2005d) standard.
Table 4.5 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of kilovoltage units Physical Parameter Tolerance/ Reference Type Suspension (IPEM, 1999) Level unless stated) Output calibration 3 % B Monitor chamber linearity (if present) 2 % B Timer end error 0.01 min B Timer accuracy 2 % B Coincidence of light and x-ray beams 5 mm CAPCA (2005d) 2 B mm Field Uniformity 5 % B HVL constancy 10 % B Measurement of HVL 10 % B Applicator output factors 3 % B
3.11. BRACHYTHERAPY
IEC 60601-2-17 (2004c) is the standard which identifies those features of design that are regarded as essential for the safe operation of the equipment and places limits on the degradation on the performance beyond which a fault condition exists. These include protection against electrical and mechanical hazards and unwanted and excessive radiation hazards (i.e. controlling timer, selection and display of treatment related parameters and leakage radiation). This safety standard requires in the technical description the statement of tolerances for radioactive source positioning, transit time and dwell time. It also limits the value for the positioning accuracy to 2 mm relative to the specified position.
The values given in Table 4.6 are based on the tolerance values in ESTRO Booklet No. 8 (2004b), AAPM Report No. 46 (1996) and the CAPCA (2006b) standard.
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All tests form part of acceptance testing. For a detailed description of test methods and conditions, please refer to the documents above. Where tests are performed routinely for quality control, suggested frequencies of testing are given in the documents indicated in the Table.
Table 4.6 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of brachytherapy equipment Physical Parameter Tolerance/ Reference Type Suspension (ESTRO, 2004B) Level Source calibration Single source when only one source used 3 % AAPM (1994) B (e.g. HDR) Individual source in a batch 5 % B Mean of batch 3 % (e.g. LDR or permanent implant)
Linear source uniformity of wire sources 5 % B Source position 2 mm B Applicator length 1 mm AAPM (1994) B Controlling timer 1 % AAPM (1994) B Transit time 1 % CAPCA (2006b) B
3.12. TREATMENT PLANNING SYSTEMS
IEC 62083 (2001b) “Requirements for the safety of radiotherapy treatment planning systems” (RTPS) is the standard which identifies those features of design that are regarded as essential for the safe operation of the equipment. It states that “the output of a RTPS is used by appropriately qualified persons as important information in radiotherapy treatment planning. Inaccuracies in the input data, the limitations of the algorithms, errors in the treatment planning process, or improper use of output data, may represent a safety hazard to patients should the resulting data be used for treatment purposes.” It is principally a software application for medical purposes and is a device that is used to simulate the application of radiation to a patient for a proposed radiotherapy treatment.
IAEA-TECDOC-1540 (2007b), addresses specification and acceptance testing of RTPSs, using the IEC 62083 (2001a) document as a basis. This document gives advice on tests to be performed by the manufacturer (type tests) and acceptance tests to be performed at the
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hospital (site tests). IAEA-TECDOC-1583 (2008a) addresses the commissioning of RTPSs. Both are restricted to photon beam planning, but IMRT is not included. Criteria for the acceptability of performance tolerances of IMRT plans, e.g. based on gamma calculations, are an area of development and are not considered in this document. The IEC has not published performance tolerances for RTPSs, and the tolerances for RTPS for photon beams in table 4.7 are taken from IAEA-TECDOC-1583 (2008a), where descriptions of test methods and conditions can also be found.
Table 4.7 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of external beam RTPSs Physical Parameter Tolerance/ Reference Type Suspension (IAEA, Level 2008a) Output factors at the reference point 2 % A Homogeneous, simple geometry Central Axis data of square and rectangular fields 2 % A
Off-axis data 3 % A Complex geometry Wedged fields, inhomogeneities, irregular fields, 3 % A asymmetric collimator setting; Central and off-axis data Outside beam edges In simple geometry 3 % A In complex geometry 4 % A Radiological field width 50% - 50% distance 2 mm A Beam fringe / penumbra (50% - 90%) distance 2 mm A
QA for treatment planning systems is described in IAEA TRS-430 (2004a), AAPM (1998b), ESTRO Booklet No 7 (2007a) for photon beams only and ESTRO Booklet No 8 (2007b) for brachytherapy and the national protocols IPEM (1999) and CAPCA (2007a).
3.13. DOSIMETRY EQUIPMENT
The quality assurance of dosimetry equipment is considered by AAPM (1994), IPEM (1999) and the CAPCA (2007c) standards. The CAPCA standard is largely based upon AAPM (1994), but with some local measurements. IPEM (1999) has the most quantitative measures. The tests from all reports are set out below in Table 4.8. For a detailed description of test methods and conditions, please refer to these documents. Where tests
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are performed routinely for quality control, suggested frequencies of testing are given in these documents.
Table 4.8 Summary of functional performance characteristics with tolerance/suspension values for acceptance testing and quality control of dosimetry equipment Physical Parameter Tolerance/ Reference Type Suspension Level (IPEM, 1999) Ionisation Chambers Leakage current 0.1 % AAPM (1994) B Linearity 0.5 % AAPM (1994) B Radionuclide stability check ≤ 1 % Calibration against secondary standard 1 % Beam Data Acquisition Systems Positional accuracy 1mm CAPCA (2000c) B Linearity 0.5 % AAPM (1994) B Ion recombination losses 0.5 % B Leakage current 0.1 % AAPM (1994) 0.5 % B Effect of RF fields 0.1 % B Stability of compensated signal 0.2 % B Standard percentage depth dose plot 0.5 % B Constancy of standard percentage depth 0.5 % B dose plot Standard profile plot: flatness 3 % B Standard profile plot: field size 2 mm B Accessories Thermometer Calibration 0.5 deg C AAPM (1994) 0.1deg C B Barometer calibration 1 mbar B Linear rule calibration 0.3 % AAPM (1994) B
3.14. RADIOTHERAPY NETWORKS
Modern radiotherapy techniques rely on the transfer of large quantities of data and images and require reliable data networks for safety and consistency. Quality control largely relates to checking the correct functionality of processes and safety software, the accuracy of new hardware and software and the comparison of data sets, sent, received or stored. Testing most often occurs with the introduction of new developments. Regular testing can be valuable to check for data corruption and hardware faults.
The guidance in this section is taken from IPEM Report 93 “Guidance for the Commissioning and Quality Assurance of a Networked Radiotherapy Department” (2006)
Page 86 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment and the parameters needing to be checked routinely are listed in Table 4.9 below. See IPEM Report 93 (2006) for a full description of the methods for checking these parameters. Reference can also be made to ISO 17799:2005 “Information Technology – Security Techniques – Code of Practice for Information Security Management” (2005) for general advice on information security and national data protection legislation may also be appropriate.
No suspension levels are given in table 4.9 because functionality must be correct for the integrity of the data and its transfer. When a loss of functionality is detected, the use of the network should be suspended until correct functionality is restored.
Table 4.9 Operating parameters to be checked routinely Operating Parameter Review of changes in assets, patch history, data stored, data disclosures, uses of data, new or changed equipment and application software Check of security fixes for Operating Systems and applications Check that anti-virus software is up to date and enabled appropriately Monitor logs for unexpected activity Monitor availability of security updates and service packs on manufacturer‟ websites Establish and monitor physical and network boundaries. Look for changes. Check physical controls are in place and are effective Communication channels Dial out: Check that dial-in is not possible after changes in system configuration or system upgrades. Check telephone numbers are dialled correctly. Check that assigned telephone numbers have not been altered. Check log records for all attempted connections, times, dates and endpoints Auto answer (dial-in): Check lists of allowed dial-in sources, allowed times and any changes in configuration settings, dial-back settings, etc. Check logs are as expected All: Monitor link error rates. Check the accuracy of data transmission. Check traffic encryption operating. Check for duplicate IP addresses. Monitor traffic for the presence of new “unexpected” protocols, promiscuous mode on interfaces or unknown devices appearing on the network Check physical integrity of cables and terminations. Monitor and document changes in physical network configuration. Monitor SNMP traffic logs for significant changes DCHP: Monitor changes in the configuration files. Test DNS/DHCP allocation is proceeding correctly. Look for new hosts in the lease allocation logs and new additions to the network Check routing tables are correct for static routes and that routed and gated daemons are functional for dynamic routes. Check for propagation of routing information outside network boundaries Check that firewall rules have not been altered. Check that only allowed hosts, services or packets are going through as new devices and applications are added to interior and exterior networks. Check firewall log for intrusion signatures Page 87 of 104 Radiation Criteria For Acceptability Of Radiological, Nuclear Medicine And Radiotherapy Equipment
Establish which common services are necessary and provide a means of monitoring and controlling access to them. Check that all essential services are operational Perform security audits of physical location of clients, servers and other critical hardware. Review access control measures and administrative personnel lists. Monitor logs for console access and machine reboots, looking for discrepancies Check logs for remote access and firewall logs for inappropriate clients or protocols Examine system logs looking for sessions that are outside expected norms Review and update the list of OSs, versions, service packs, applications and patch levels. Test applied patches and updates as required in accordance with manufacturer‟s instructions Perform checks for new MAC addresses on the network (DHCP does this automatically). Check that unused ports are disabled and/or unpatched. Check that used ports are set to fixed MAC addresses where possible Check the operation and configuration of the authentication system. Check the signatures for the configuration files. Check password change dates are operating as planned. Check that back door or manufacturer‟s passwords are not enabled or are changed regularly Monitor accounts added to the system for excessive permissions. Monitor system logs for invalid administration log-in attempts Transfer test data and checksum. Check for the addition of new fields and data types on host systems. For DICOM transfers, use the DICOM ECHO verification service to check connectivity and handshaking. For HL7 transfers, check connectivity Check backup logs for errors and omissions, and error rates to verify the media is good and hardware is not failing. Backup policy must include a retirement age for media. Destroy data no longer required. Practice disaster recovery regularly Review data flows looking for new cached items. Run reports checking the coherency of the data across the system Check for the effect of software upgrades, new equipment added, changes in configuration and data files. Check the signatures of significant files and update if necessary. Verify that the change control process is working Perform checks that permissions and shares have not changed from those expected Monitor available space, CPU utilisation and use of swap memory on critical devices Check NTP client logs for synchronisation failures. Check reference time sources for offset and stability. Check that server and client time zone settings have not been modified. Check system time against an independent time source Check that record locking on files and databases have not been broken after any OS changes including service packs, client set-up changes and upgrades Data Unique identification Geometric integrity and scaling Region of acceptability of data accuracy and integrity Coordinate frame orientation and location Patient orientation and specification within the coordinate frame Tolerances on images with respect to pixel values geometric distortion
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APPENDIX 1 INFORMATIVE NOTE ON IMAGING PERFORMANCE
The general purpose of medical imaging is to obtain adequate image quality at the lowest possible radiation burden to the patient. Assessment of image quality is, therefore, important. Various methods are available for quantification of image quality (Table DR1.1 based on ICRU Report 54, 1995).
Table A1.1 Assessment of (image) quality at various physical/medical levels Approach Methods used Physical (fundamental) image quality Large-scale transfer function (characteristic curve), spatial resolution (transfer function), noise (noise power spectra) Statistical decision theory Ideal observer formalism, other observers Psychophysical approach (ROC) analysis, contrast detail method Quality assessment using phantoms for a Specific test objects, e.g. for high and low contrast specific imaging task spatial resolution Examination of images of patients European image quality criteria (diagnostic radiographic and CT images)
The methods range from those requiring high levels of expertise and facilities (transfer functions), are very elaborate (ROC analysis) to methods which are in principle applicable in the field in a department of radiology.
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APPENDIX 2 AUTOMATIC EXPOSURE CONTROL
Methodology, CR and DDR
CR, DDR and AEC
The following Tables provide additional information in connection with CR and DDR AEC. They are complementary to the data in Section 2.2 of the text.
Table A2.1 Acceptability criteria for the AEC device (CR) Physical parameter Suspension Level Reference Criterion Notes Consistency between Mean ± 20% IPEM B Attenuation chambers (2005a) material Repeatability Mean ± 30% IPEM B Attenuation (2005a) material Consistency Mean ± 60% IPEM B Attenuation (2005a) material Image receptor dose Speed Class 400: IPEM B Dosemeter. > 2.5 µGy± 60% (2005a) 1mm-2mm Speed Class copper filter 200: > 5 µGy± 60%
Table A2.2 Acceptability criteria for AEC device (DDR) Physical parameter Suspension Reference Criterion Method Level Consistency between IPEM (2005a) B Attenuation chambers material Repeatability Mean ± 30% IPEM (2005a) B Attenuation material Consistency Mean ± 60% IPEM (2005a) B Attenuation material Image receptor dose Manufacturers IPEM (2005a) B Dosemeter, Specification ± 1.0mm copper. 60%
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APPENDIX 3 EQUIPMENT
Quality Control Equipment for Radiology
Calibration
Instruments should have calibration traceability. Dosimetric instrumentation should comply with IEC (1997b) and follow international guidelines (IAEA, 2004b). Care should be taken for measurements in the beam conditions outside of those defined by IEC (1997b) (e.g. some situations in mammography, computed tomography and interventional radiology and all situations involving scatter radiation). In these conditions the use of instruments with a small energy response variation is strongly encouraged. Field (or clinical) KAP meter calibration should be performed in situ using a calibrated reference instruments using one of two methods as described in IAEA (2007a) and Toroi, Komppa and Kosunen (2008).
Some useful equipment
Radiographic instrumentation Calibrated non invasive tube kVp meter (IAEA, 2007a) Dosimeter calibrated in terms of air kerma free-in-air with specialized detectors for measurements in different modalities (ICRU, 2005; IAEA, 2007a). Indication of current exposure time product (on the x-ray unit or by ancillary equipment). Instrument calibrated for measurement of exposure time.
Auxiliary equipment Accurate tape measure and steel rule Aluminium filters (type 1100, purity > 99%) ranging from 0.25 mm to 2 mm (HDWA, 2000). Lead rubber sheet(s). Attenuator set and supports Radio-opaque grid or equivalent Collimation and Alignment tools: X-ray field mapping device, e.g. radiographic film, Gafchromic film or equivalent. Radio-opaque markers – coins or paper clips. Small lead or copper block Film Screen Contact Test Tool (Mesh Test Tool). Non-mercury thermometer, with a range of 25-40 oC and an accuracy of ± 0.1oC. Geometry test object High contrast resolution tool (Hüttner 18)
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Phantoms Standard CT dose phantoms, Body 32-cm PMMA, Head 16 cm PMMA CT uniformity (water) phantoms Slice thickness phantom; Inclined planes – axial acquisition, Thin disc or bead Measurements to assess the performance of DXA units may have to be performed using test equipment, some of which is specifically designed for that purpose PMMA phantoms of 10, 12, 15, 18 and 20 cm thickness. Standard phantom, e.g.: European Spine Phantom [7, 12], BFP [8]
Tomography Test tool (BIR, 2001; IPEM, 1997b). Test tool for angle of swing, i.e. a 45º foam pad, pin-hole or other appropriate test tool (IPEM, 1997b)
Instrumentation for light and image display Calibrated Photometer for measuring luminance and illuminance. Test pattern Image such as SMPTE or T018-QC Calibrated Sensitometer with 21 steps or pre-exposed sensitometry strips. Calibrated Densitometer, accuracy of ± 0.01 OD.
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IEC (1994b) International Electrotechnical Commission. IEC 61223-2-5 Ed 1.0: Evaluation and routine testing in medical imaging departments - Part 2-5: Constancy Tests - Image display devices. Geneva: IEC.
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ACKNOWLEDGEMENTS
Coordinator: Dr Keith Faulkner Diagnostic Radiology Lead: Prof Jim Malone Nuclear Medicine Lead: Dr Stelios Christofides Radiotherapy Lead: Prof Stephen Lillicrap
Contributors Reviewers
Diagnostic Radiology Dr Tamas Porubszky Dr Steve Balter Mr S. Szekeres Dr Norbert Bischof Markku Tapiovaara Dr Hilde Bosmans Kalle Kepler Ms Anita Dowling Koos Geleijns Aoife Gallagher Simon Thomas PhD FIPEM Remy Klausz Geraldine O‟Reilly Dr Lesley Malone Ian (Donald) Mclean Dr Alexandra Schreiner Dr Eliseo Vano Colin Walsh Dr Hans Zoetelief
Nuclear Medicine Dr Inger-Lena Lamm Dr Soren Mattsson
Radiotherapy Prof Patrick Horton Dr Inger-Lena Lamm Dr Wolfgang Lehmann
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