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Code of Practice for the Safe Use of Ionizing Radiation in ...

  1. 1. Code of Practice for the Safe Use of Ionizing Radiation in Veterinary Radiology Reprinted from the Report of the 93rd Session of the Council, June 1982 © Commonwealth of Australia, 1983 Australian Government Publishing Service, Canberra 1983 Printed by McCarron Bird, Melbourne R79/802(10) The NHMRC has rescinded this publication in accordance with its policy of reviewing documents published more than 10 years ago. The NHMRC policy with regard to rescinded documents/publications can be found at ARPANSA has taken over responsibility of the review process for this publication. Continued use of publications is subject to the individual requirements of the relevant regulatory authority in each jurisdiction. The relevant authority should be consulted regarding the use of the advice contained in this publication. All publications in the Radiation Health Series will be progressively reviewed by ARPANSA’s Radiation Health Committee and, where appropriate, will be re-published as part of the ARPANSA Radiation Protection Series. Enquiries about the Radiation Health Series publications should be forwarded to the ARPANSA Standards Development and Committee Support Section, 619 Lower Plenty Road, Yallambie, Victoria, 3085. Tel: 03 9433 2211, Fax: 03 9433 2353, Email:
  2. 2. 117 Appendix XXI Code of practice for the safe use of ionizing radiation in veterinary radiology CONTENTS Part I - General Section 1 - Introduction 1.1 Need for this Code 1.2 Scope of this Code 1.3 Application of this Code 1.4 Dose limits 1.5 Categories of exposed persons 1.6 Risk of radiation injury 1.7 Specialised meanings for ‘shall’ and ‘should’ Section 2 - Responsibilities and Radiation Surveillance 2.1 Overall responsibility 2.2 Responsibility of User for radiation protection 2.3 Legislative requirements 2.4 Designation of radiation workers 2.5 Personal monitoring 2.6 Radiation monitoring records 2.7 Radiation surveys Part II - Diagnostic Radiology Section 3 - Procedures and Facilities 3.1 Introduction 3.2 Facilities - General 3.3 Radiography in defined X-ray rooms or areas 3.4 Reduction of radiation hazards 3.5 Restraint of animals 3.6 Radiography outside defined X-ray rooms or areas 3.7 Fluoroscopic procedures ANNEXE I Statutory Authorities within Australia ANNEXE II Bibliography ANNEXE III Biological effects of ionizing radiation and limits in exposure to such radiation. ANNEXE IV Personal monitoring services within Australia ANNEXE V Ancillary equipment ANNEXE VI Processing of exposed radiographs ANNEXE VII Warning signs
  3. 3. 118 Part I - General Section I - Introduction 1.1 Need for this Code There is widespread use of X-rays for diagnostic purposes and a growing use of X-rays, beta rays and gamma rays for therapeutic purposes in veterinary practice as well as in teaching and research. Whenever these radiations are used on animals, there is considerable potential for persons involved in such practices to be exposed to the radiation hazards that could arise from them. Guidance is therefore needed on the protective measures and procedures that should be adopted to ensure, first, that any limits prescribed with respect to exposure of persons are not exceeded, and second, that such exposure is kept as low as reasonably achievable. 1.2 Scope of this Code This code applies to the use of ionizing radiation in the practice of veterinary science, teaching and research and embraces both diagnostic radiology and radiotherapy. The code is in three parts: Part I General Part II Diagnostic Radiology Part III Radiotherapy Note: Part III will be issued separately at a later date. 1.3 Application of this Code This Code has been prepared to supplement the radiation control legislation enacted in Australia and implemented by the appropriate statutory authorities (see Annexe I). Advice on this legislation and on any aspects of the implementation of this code should be sought from these authorities. This code is intended as a guide to safe practices and should be applied with sound judgement to specific situations. It is recommended that establishments draw up their own detailed working procedures based on the relevant legislation and this code, and that they issue appropriate instructions to all workers who may be exposed to radiation in the course of their duties. The code lays down detailed requirements for the following protective measures: (a) allocation of responsibility for all safety procedures and radiation surveillance, (b) provision of appropriate premises and installations, (c) provision of appropriate radiation and ancillary equipment, and (d) provision of appropriate maintenance and safety checking of equipment. The application of these measures will ensure that the prescribed dose limits with respect to exposure of persons will not be exceeded and that any unnecessary exposure will be minimised. 1.4 Dose limits Radiation doses greatly exceeding those normally received from natural background radiation are known to cause harm and in particular to increase the risk of cancer. It is not known, however, if harmful effects are induced at low doses and low dose rates which are comparable to or slightly in excess of those of background radiation. Because of this, it is cautiously assumed that any exposure to radiation may entail some risk and that the risk is proportional to the dose received, down to the lowest dose. Accordingly, limits of radiation dose for persons undertaking work with radiation and radioactive substances are chosen so that the risks arising from the average doses received in that work are no greater than risks in other occupations that have high standards of safety.
  4. 4. 119 Likewise, limits of radiation dose for the public are chosen so that the risks to them are no greater than other risks considered acceptable in everyday life. The doses chosen to limit the risks forma set of dose limits. Dose limits are applied in operations involving radiation and radioactive substances to ensure that the upper limits of the risks to health of the exposed persons and of society are appropriately small. They have been prepared as Radiation Protection Standards for the National Health and Medical Research Council, which has published them in Recommended radiation protection standards for individuals exposed to ionizing radiation (see Annexe II). Council has recommended that these Standards be used throughout Australia. Background information on the biological effects of ionizing radiations and a summary of the dose limits given in these Standards are in Annexe III. Further advice on interpretation and application of the Standards and dose limits is available from the appropriate statutory authority. 1.5 Categories of exposed persons Radiation Protection Standards are considered for two categories of exposed persons. These are: (a) radiation workers, i.e. persons who, in the course of their employment may be exposed to ionizing radiation arising from their direct involvement with sources of such radiation, and (b) members of the public. Radiation workers include all members of a department or practice, including temporary or visiting staff whose duties are likely to require their presence during radiographic and radiotherapeutic procedures. Members of the public include all other persons, e.g. owners of animals, observers, receptionists, family of staff members living adjacent to the premises used for radiography, etc. 1.6 Risk of radiation injury If the provisions of this code are applied carefully and consistently, the dose limits will not be exceeded and the risk of radiation injury will be slight. However, if the dose limits laid down in the Radiation Protection Standards are exceeded by a large factor in a single exposure or in a number of exposures over a short period of time, or are exceeded over a long period, injury may result. Attention is drawn to the manner in which the dose limits may be exceeded in relation to the veterinary practice. 1.6.1 In radiography, the principal hazard arises from the possibility of exposure to the primary X-ray beam. Scattered radiation and radiation leaking from the X-ray tube assembly, which are always present during an exposure, may also contribute further significant doses. 1.6.2 In radiotherapy, the radiation dose delivered to the patient is very much greater than in diagnostic procedures and thus the potential hazard may be very much greater to the operator. 1.7 Specialised meanings for ‘shall’ and ‘should’ The words ‘shall’ and ‘should’ and ‘should’, where used in this Code have specialised meanings. ‘Shall’ indicates that the particular requirement is mandatory. ‘Should’ indicates a requirement that is to be applied as far as practicable, in the interest of reducing radiation risks.
  5. 5. 120 Section 2 - Responsibilities and Radiation Surveillance 2.1 Overall responsibility The responsibility for radiation protection lies with the person in control of the institution, department or practice using the X-ray equipment and/or radioactive substances. This person is referred to as the User for the purposes of this Code. In some circumstances the User may appoint a Radiation Safety Officer to act for him. The User or Radiation Safety Officer shall have the authority and sufficient professional or technical training to enable him to implement this code. 2.2 Responsibility of User for radiation protection The User shall determine the work procedures and provide all the facilities and/or equipment that are necessary to enable the implementation of this code. 2.3 Legislative requirements The User shall ensure that he is familiar with all requirements of the appropriate statutory authority including registration, licensing, monitoring, recording of personal doses, reporting, surveying, maintenance and quality control checks. 2.4 Designation of radiation workers The User shall determine which staff are to be designated 'radiation workers' under subclause 1.5(a). This shall include all veterinary surgeons, veterinary nurses, and others who are likely to be present during radiographic and radiotherapeutic procedures. 2.5 Personal monitoring 2.5.1 The dose of ionizing radiation from external sources received by a radiation worker shall be monitored in accordance with the requirements of the statutory authority. If personal monitoring is required, monitors should be worn on the body at chest or waist height during the period of occupational exposure. When lead protective aprons are worn, monitors should be worn under the aprons. In some cases it may also be necessary to measure the dose to other parts of the body, for example to the hands and forearms, so as to ascertain that the relevant dose-equivalent limits are not exceeded. (Personal monitors can be obtained from the Radiation Monitoring Services listed in Annexe IV.) 2.5.2 It may be advisable for visitors or other staff, who occasionally enter areas normally occupied by radiation workers, to wear monitors during their occupancy of such areas so that the radiation levels to which such persons are exposed can be ascertained and shown to be satisfactorily low. 2.6 Radiation monitoring records 2.6.1 Radiation dose records shall be maintained by the User for each radiation worker as required by the statutory authority. They shall show any doses received during the present period of employment and also doses received as a result of previous employment in which ionizing radiations were used. Radiation dose records provide information on the doses received and indicate the efficacy of the safety procedures that have been implemented. They shall be available for inspection by the individual workers concerned and the statutory authority. 2.6.2 When an employee is first designated as a 'radiation worker' his employer shall request from the employee's previous employer a copy of the radiation dose record for that employee.
  6. 6. 121 2.7 Radiation surveys 2.7.1 Plans for buildings that are to incorporate radiographic or radiotherapeutic facilities shall be submitted to the statutory authority. 2.7.2 The User in consultation with the statutory authority shall ensure that appropriate radiation safety assessments are made. These will be required in the following circumstances: (a) Before the installation is put into routine use. (b) If the installation or working procedures are modified. 'Modified' means a change in the amount of radiation, the manner of its use or a change in the X-ray equipment or its location. Such modifications may mean the original protection is no longer adequate. (c) If personal monitoring indicates that the doses received by any person exceed, or are likely to exceed the appropriate dose-equivalent limits or are higher than normal for no obvious reason, or are significantly higher than average doses received in similar departments and practices. (d) If changes are made in the immediate environs, for example a store or waiting area may become an office, resulting in a change of occupancy. (e) If there is a significant increase in work load in the department or practice. (f) Whenever any servicing is carried out on the X-ray tube assembly. 2.7.3 If the radiation safety assessment indicates that any person may receive doses in excess of the appropriate dose-equivalent limits, the User shall notify the statutory authority.
  7. 7. 122 Part II - Diagnostic Radiology Section 3 - Procedures and Facilities 3.1 Introduction 3.1.1 Radiography shall be undertaken only if there is a definite indication for the procedure and if it can be performed without undue radiation hazard. 3.1.2 Radiography shall be carried out only by appropriately trained and qualified personnel. 3.1.3 In radiography, no part of any person, even if shielded by protective clothing, shall be exposed to the primary X-ray beam, In fluoroscopy, no part of any person shall be exposed to the primary beam unless it is adequately shielded by protective clothing (see 3.2.7). Fluoroscopy shall be carried out in accordance with the requirements of 3.7. 3.1.4 Only persons who are essential to a procedure shall be present during radiographic and fluoroscopic examinations. These persons shall be properly instructed and should understand their part in the proposed procedure. All such persons shall position themselves behind protective screens, except where this is not practicable, in which case they shall wear protective aprons and remain as far as practicable from the primary X-ray beam, the animal and the X-ray tube assembly. 3.2 Facilities - General 3.2.1 In general, radiography may be considered in two categories. (a) Radiography within a defined X-ray room or area. (b) Radiography outside a defined X-ray room or area when a mobile or portable X-ray machine is taken to the animal. 3.2.2 X-ray machines shall have sufficient capacity to provide radiographs of good diagnostic quality. In addition, adequate facilities to provide control over the animal and protection of the operator are necessary. As these are best provided in a defined X-ray room or area, radiography outside such areas shall be carried out only where it is not practicable to bring the animal to that area. 3.2.3 All X-ray equipment shall comply with the relevant parts of the following Australian Standards and with any variations or additions required by the appropriate statutory authority. AS 2398 -1980 Fixed Diagnostic X-Ray Equipment - Design, Construction and Installation -Safety Requirements. AS 3201.5 -1977 Dental and Mobile Medical X-Ray Machines. See Bibliography Annexe II concerning availability of these standards. Any subsequent revisions of these standards shall be complied with as above. Advice on interpretation of these standards and on tests for compliance with the requirements should be obtained from the appropriate statutory authority. Tests for compliance shall be carried out at regular intervals in accordance with requirements of the statutory authority.
  8. 8. 123 3.2.4 An examination table shall be provided with either protective shielding equivalent to 0.5 mm lead on the sides or with protective shielding equivalent to 1 mm lead underneath the table top and any Potter-Bucky diaphragm incorporated in the table. For ease of cleaning and to prevent mechanical damage the lead shielding should be covered with laminated plastic sheeting. 3.2.5 Sand bags, v-troughs, slings, adhesive tape or other positioning and immobilising devices shall be available for supporting the animal during radiography (see Annexe V). 3.2.6 Suitable cassette holders shall be available for use when using horizontal or angled X-ray beams. If they are not self supporting, they shall be fitted with handles at least 1 metre long and a ground support to ensure that a person holding them can remain well outside the primary beam (see Annexe V). 3.2.7 Personal protective devices made of lead impregnated rubber or plastic such as aprons, gloves and shields suitable for hand and forearm, shall be provided for all persons who are required to be present during radiography and who are not protected by fixed or mobile protective screens. Such protective devices shall have a lead-equivalent thickness throughout of not less than 0.25 millimetre, and of not less than 0.5 millimetre when energies above 100 kV peak are used. These lead protective devices shall be examined both visually and radiographically on a regular basis (e.g. three-monthly for a practice with a heavy X-ray work load) to ensure that their shielding efficiency has not become impaired by cracks due to sharp folds, penetrations which could be caused by claws, or other damage. When not in use aprons should be hung without folds on appropriate hangers. 3.3 Radiography in defined X-ray rooms or areas 3.3.1 A defined X-ray room or area for veterinary radiography shall consist of: (a) a space of adequate dimensions; (b) radiation shielding provisions for persons within and outside the room area, (c) means of restricting access to the room or area, (d) X-ray warning signs at all entrances (See Annexe VII), (e) facilities for positioning and immobilising the animal, and (f) an X-ray machine of adequate capacity and appropriate type to undertake the required radiographic examination. 3.3.2 All small animal radiography should be carried out in a defined X-ray room or area. 3.3.3 Advice on all shielding requirements for defined X-ray rooms or areas should be obtained from the appropriate statutory authority. However, the need for structural shielding is reduced by, whenever possible, directing the X-ray beam vertically down with the animal placed on an X-ray table. Single clay brick walls or equivalent normally afford adequate protection for adjoining areas. For horizontal X-ray beams additional shielding may be required. 3.3.4 The X-ray work load for a given period may be calculated by summing the products obtained by multiplying the X-ray tube current by the time for each exposure during that period. If the X-ray work load exceeds 2000 milliampere seconds per week a protective screen incorporating a viewing window of protective glass shall be provided between the operator and the X-ray tube assembly. Such a screen should be at least 2 metres high and at least 1 metre wide. The lead equivalent of the screen, including the window, shall be not less than 0.5 millimetre and the lead or other protective material in the screen shall
  9. 9. 124 adequately overlap at any joins and around the viewing window. Advice on screen requirements should be sought from the appropriate statutory authority. 3.4 Reduction of radiation hazards 3.4.1 The radiation dose to staff shall be minimised by: (a) Taking all practical precautions to avoid unnecessary repetition of radiographs. (b) Ensuring that the primary beam is restricted to the area to be examined by means of the collimator. (c) Using the fastest film and film-intensifying screen combination compatible with acceptable image quality. (d) Ensuring cleanliness and maintenance of cassettes and intensifying screens. (e) Ensuring that all assistants receive clear instructions on the procedure to be undertaken and understand their part in it. (f) Ensuring that all assistants remain behind the protective screens, or if there is no screen, wear protective clothing and position themselves as far as practicable from the X-ray tube assembly, the animal and the path of the primary X-ray beam. (g) Ensuring that the exposure is not made until the animal is properly restrained and positioned. (h) Ensuring that appropriate film processing facilities are available and are used correctly. (See Annexe VI). 3.4.2 Cassette holders shall be used whenever a cassette cannot be supported on a table, on the ground or on another support. A person supporting a cassette holder shall remain well outside the primary beam. 3.4.3 During radiography no person shall hold the X-ray tube assembly or the cassette. The X-ray tube assembly shall be rigidly supported by a holder or stand which provides adequate stability and does not allow movement blurring of the radiograph. 3.4.4 Routine working procedures for radiography shall be devised. The procedures shall be appropriate to the type of work carried out in the establishment and shall include appropriate precautions to reduce radiation exposure, positioning requirements for animals and exposure techniques. They shall be followed by persons carrying out and assisting with radiography and shall be posted in the X-ray areas. 3.4.5 Reference should be made also to Australian Standard AS -"Guide to good radiological practices" (in preparation). 3.5 Restraint of animals 3.5.1 The animal shall not be held for radiography unless for clinical reasons other means of immobilisation are not practicable. Immobilisation should be achieved by mechanical means, by tranquillisation or by anaesthesia. These methods will eliminate or reduce the radiation hazard from manual restraint and assist in the reduction of image blurring due to movement. Advice on mechanical restraints is given in Annexe V. 3.5.2 When, in exceptional circumstances, manual restraint is necessary, the following procedures shall be adopted: (a) The animal shall be restrained by the minimum number of persons necessary.
  10. 10. 125 (b) All persons shall position themselves as far as practicable from the path of the primary X-ray beam, the animal and the X-ray tube housing. No part of any person shall be in the direct X-ray beam. (c) Persons holding the animal shall wear protective gloves and aprons. (d) If necessary, persons not normally exposed occupationally to ionizing radiation (for instance the owners of the animal) may be asked to hold the animal, provided that any reduction in control that results will not significantly increase the radiation hazard of the procedure. Children and pregnant women shall not hold animals during radiography and a notice to this effect shall be displayed prominently in the X-ray area. (e) When it is necessary for staff to hold an animal during radiography, one individual should not be asked to hold an animal repeatedly. Pregnant staff members should not hold animals during radiography. 3.5.3 The radiography of large animals, e.g. horses and cattle, creates additional problems in relation to radiation hazards for the following reasons: (a) It is seldom practicable to anaesthetise the animal and some form of manual restraint is likely to be needed. (b) It is often necessary for the film cassette holder to be supported manually. (c) It is usually necessary for the useful beam to be directed horizontally. Thus there is a greater risk of irradiating assistants. (d) Those who restrain the animal or support the cassette holder are more likely to have their attention concentrated on their task rather than on avoiding the useful beam. (e) Radiography of regions other than the lower limbs requires the use of considerably greater exposure factors that will increase the hazard both from the primary beam and from scattered radiation. Such examinations should be carried out only on high powered X-ray equipment at a fixed installation. (f) The illumination of the light beam collimator may be ineffective due to the light levels out of doors and in such circumstances there is a tendency to increase the area of the X-ray beam to an excessive size. From this point of view, it is preferable for outdoor radiography to be done in the shade. If a light beam collimator is not provided with an indication of the beam size at the various focus-film distances used, or if the illumination is inadequate, additional cones or aperture diaphragms shall be used during outdoor radiography to restrict the beam to the size of the X-ray film used. Each cone shall be labelled with the beam size at the focus-film distance to be used. 3.5.4 In view of the additional radiation hazards in radiography of large animals, there is a particular responsibility to ensure that, despite all difficulties, all precautions are observed. The following precautions shall be taken: (a) The animal should be suitably tranquillised or anaesthetised whenever possible prior to radiography. (b) All assistants shall wear sufficient protective clothing to give full protection from the source of radiation (for example, it may be necessary to protect the legs). (c) All assistants not immediately required for the procedure shall remain at a safe distance.
  11. 11. 126 3.6 Radiography outside defined X-ray rooms or areas 3.6.1 Radiography of animals outside defined X-ray rooms or areas (in other parts of the premises, or on visits to farms, stables or kennels) is likely to add to the radiation risks for the following reasons: (a) The usual ancillary and protective equipment may not be available. (b) It is likely to be more difficult to immobilise the animal. (c) The assistants may be untrained. (d) It is likely to be more difficult to prevent the presence of unauthorised persons during radiography. (e) There is a greater risk of irradiating persons in nearby areas. (f) The light beam collimator may be ineffective (see 3.5.3 (f)). 3.6.2 When it is necessary to radiograph animals outside defined X-ray rooms or areas, it shall be ensured that: (a) The necessary equipment, such as cassette holders, is available. (b) Sufficient protective clothing is available for all persons taking part. (c) The number of assistants is kept to the minimum necessary for the procedure. (d) The nature of the procedure and the precautions to be observed are carefully explained to the assistants before the radiographic exposures are made. (e) Adequate precautions are taken to prohibit the access of unauthorised persons to the area during radiography (e.g. by display of warning signs - see Annexe VII). (f) The dose to members of the public, i.e. persons passing by or in adjoining rooms or areas, is limited. (g) Adequate supports for the X-ray tube assembly and cassettes are provided. In no circumstances is any person to hold these directly (see 3.4.3). (h) Means are provided to achieve the correct alignment of the X-ray beam to the cassette and to ensure that the X-ray beam is collimated to an area equal to or less than the cassette (see 3.5.3 (f)). 3.7 Fluoroscopic procedures 3.7.1 Fluoroscopy is potentially more hazardous than radiography, because the product of exposure time and X-ray tube current is usually greater in the former and because the operators stand nearer the primary beam and the animal. Since the detail that can be visualised in fluoroscopy in inferior to that which can be seen radiographically, the additional risks of using fluoroscopy as a substitute for radiography cannot be justified. Fluoroscopy is indicated only in circumstances in which it is essential to study movement. When indications are sufficiently definite for fluoroscopy, it shall be carried out only if suitable equipment is available and by veterinary or medical personnel trained and experienced in this technique. 3.7.2 An X-ray image intensification system shall be used. It shall be properly installed and subject to service and maintenance at least once per year. A remote television display should be used for group viewing and teaching purposes. 3.7.3 It should be noted that because of the greater potential hazard, the use of fluoroscopy may require special approval from the statutory authority.
  12. 12. 127 ANNEXE I STATUTORY AUTHORITIES WITHIN AUSTRALIA In parts of this code, reference is made to the appropriate statutory authority. The appropriate contacts for matters relating to the statutory requirements of the authorities in the States and Territories are: 1. AUSTRALIAN CAPITAL TERRITORY Consultant, Radiation Safety Telephone: (062) 43 2111 Capital Territory Health Commission P.O. Box 825 Canberra City, A.C.T. 2601 2. NEW SOUTH WALES Officer-in-Charge Telephone: (02) 646 0222 Radiation Branch Division of Occupational and Environmental Health Health Commission of N.S.W. P.O. Box 163 Lidcombe, N.S.W. 2141 3. NORTHERN TERRITORY Physicist Telephone: (089) 80 2911 Occupational Health Branch N.T. Department of Health P.O. Box 1701 Darwin, N.T. 5794 4. QUEENSLAND Director Telephone: (07) 224 5611 Division of Health and Medical Physics Department of Health 535 Wickham Terrace Brisbane, Qld 4000 5. SOUTH AUSTRALIA Senior Health Physicist Telephone: (08) 218 3211 Occupational Health and Radiation Control Branch South Australian Health Commission G.P.O. Box 1313 Adelaide, S.A. 5001 6. TASMANIA Health Physicist Telephone: (002) 30 6421 Division of Public Health Department of Health Services P.O. Box 191B Hobart, Tas. 7001 7. VICTORIA Senior Scientific Officer Telephone: (03) 616 7777 Occupational Health Services Health Commission of Victoria 555 Collins Street Melbourne, Vic. 3000
  13. 13. 128 8. WESTERN AUSTRALIA The Secretary Telephone: (09) 380 1122 Radiological Council State X-ray Laboratory Department of Public Health Verdun Street Nedlands, W.A. 6009
  14. 14. 129 ANNEXE II BIBLIOGRAPHY 1. National Health and Medical Research Council Recommended radiation protection standards for individuals exposed to ionising radiation. AGPS, Canberra, 1981. This publication is available from the appropriate statutory authority listed in Annexe I. 2. Australian Standards AS 2398 - 1980 Fixed diagnostic X-ray equipment - design, construction and installation - safety requirements AS 3201.5 – 1977 Dental and mobile medical X-ray machines AS Guide to good radiological practices (in preparation) Australian Standards are obtainable from the offices of the Standards Association of Australia NEW SOUTH WALES 80 Arthur Street WESTERN AUSTRALIA North Sydney 2060 11-13 Lucknow Place Telephone: 929 6022 West Perth 6005 Telex: 26514 Telephone: 321 7763 Telegrams: Austandard, North Sydney TASMANIA 18 Elizabeth Street 51 King Street Hobart 7000 Newcastle 2300 Telephone: 34 6911 Telephone: 2 2477 VICTORIA QUEENSLAND 191 Royal Parade 447 Upper Edward Street Parkville 3052 Brisbane 4000 Telephone: 347 7911 Telephone: 221 8605 Telex: 33877 SOUTH AUSTRALIA NORTHERN TERRITORY 11 Bagot Street C/- Master Builders Association North Adelaide 5006 191 Sturt Highway Telephone: 267 1757 Darwin 5790 Telephone: 81 9666
  15. 15. 130 ANNEXE III BIOLOGICAL EFFECTS OF IONIZING RADIATION AND LIMITS IN EXPOSURE TO SUCH RADIATION. Note: This statement provides background information. Not all of it is relevant to this Code. Considerable knowledge has been gained during this century, and particularly during the past three decades, on the possible biological effects of ionizing radiation on man. These effects may manifest themselves in the exposed individual and they are then referred to as somatic effects or they may arise in the descendants of the exposed individual, in which case they are referred to as hereditary effects. It is important to recognise, however, that many of the biological effects that can be caused by ionizing radiation may also result from exposure to other agents and it is not always possible to determine the cause of an effect. Man has always been exposed to radiation, and this arises from terrestrial sources, cosmic radiation and radionuclides deposited in the body. This natural background radiation varies from place to place on the earth, but generally results in individuals receiving between 800 and 1500 microsievert1 (µSv) per year, although there are a few places where the terrestrial levels are very much higher than elsewhere. The levels of exposure from this radiation are such that it is not possible to ascribe any of the ill-effects in man specifically to this radiation. On the other hand, radiation-induced effects have been observed in man when individuals have been exposed to very large radiation doses and it is from such doses that our knowledge of biological effects from radiation exposure is derived. Injury to tissue became evident in the past from a number of different sources - for example, as a result of using radium luminous compounds for painting dials on watches and instruments, many workers developed bone sarcoma; some miners working in uranium mines developed lung cancer; some radiologists developed skin erythema and leukaemia when not using adequate radiation protection; and there was a small excess of leukaemia and other malignant diseases above the expected incidence rates among survivors of the atomic bombs in Hiroshima and Nagasaki in Japan following exposure to radiation. In all the above examples, and there are many more demonstrated radiation-induced effects, the doses received by individuals were very large - many times the dose arising from natural background radiation. The effects arising from large radiation doses are well known and many studies have been undertaken in order to correlate radiation-induced effects with smaller doses. However, it has not been possible to confirm that the incidence of effects is directly related to the doses received as the statistics available for such studies have been inadequate. Accordingly studies have been carried out on animals and plants to determine if there is any correlation with them between effects and dose delivered and dose rate. It has been shown that the incidence of many biological effects produced is related to the total dose delivered, whilst for other effects, there appear to be threshold doses below which those effects may not occur. Whilst it is not possible in all cases to extrapolate the results of these studies to man, they serve a very useful purpose in identifying possible dose-effect relationships. The effects arising from exposure to ionizing radiation fall into two categories. Stochastic effects are those for which the probability of an effect but not the severity of the effect occurring is regarded as a function of the dose to which the individual is exposed. It is considered that there is no threshold dose below which the probability of such an effect occurring is zero. On the other hand, non-stochastic effects are those for which the severity of the effect varies with the dose to which the individual is exposed and a threshold may occur, below which such an effect does not occur. From the studies undertaken, it is known that the induction of malignancies, including leukaemia is a stochastic effect of radiation, although such malignancies may not become manifest until many years after the radiation exposure. Mutagenic effects are also stochastic effects and these may be propagated through the population for many generations. Defects arising from such mutations are 1 The sievert is the unit used in radiation protection for dose equivalent and is equal to 100rem. 1 µSv = 10-6 Sv; 10 µSv = 1 mrem.
  16. 16. 131 only likely to become apparent in the first or second generation following irradiation of an individual. A defect causing slight physical or functional impairment, and which may not even be detectable, will tend to continue in the descendants, whereas a severe defect will be eliminated rapidly through the early death of the zygote or of the individual carrying the defective gene. The risk of mutagenic effects arising will decrease with increasing age of the irradiated individuals due to their decreasing child expectancies with age. Non-stochastic effects arising are specific to particular tissues, for example, non-malignant damage to the skin, cataract of the eye, gonadal cell damage leading to impaired fertility etc. For many of these effects a minimum or threshold dose may be required for the effect to be manifest. If an individual receives a dose greatly in excess of the threshold dose the manifestation of the effect will occur in a relatively short period after the irradiation. However if the dose is not greatly in excess of the threshold dose many of the resulting effects will be of a temporary nature and reversion to normal conditions usually occurs. From our knowledge of biological effects arising from exposure to radiation, it is possible to identify the risks of stochastic effects occurring with the doses received by the various organs and tissues of the body. These risks are derived from exposure of persons to very high doses and from studies on animals etc. As there is very little information on the effects of exposure to low doses it is cautiously assumed that risk is directly proportional to dose, right down to zero dose and that there is no threshold below which these effects do not occur. These assumptions may lead to overestimates of the risks associated with exposure to low doses of radiation. Although the risks derived from such assumptions may be very small, it is important that they are kept small by ensuring that all radiation exposure of individuals is kept As Low As Reasonably Achievable (referred to as the ALARA principle) and that there be a demonstrated net benefit for each exposure. Radiation protection is concerned with the protection of individuals involved in various radiation practices as well as with the protection of members of the public. It recognises that various practices involving radiation exposure are necessary for the well-being of individuals and for the good of mankind. In undertaking such practices, individuals as radiation workers or as members of the public, may be irradiated and the exposure resulting from those practices must be minimised in accordance with the ALARA principle. Good radiation protection practice requires the setting of standards of occupational exposure and these are such that the risk of fatalities arising from radiation-induced malignancies from the average doses received in such exposure is no greater than the risk of fatalities arising in other occupations that have high standards of safety. Radiation Protection Standards have been prepared for the National Health and Medical Research Council (1) for use in Australia and are based on the recommendations of the International Commission on Radiological Protection (2). They assume for stochastic effects a linear relationship between risk and dose and that there is no threshold dose below which effects do not occur. For non-stochastic effects relating to specific organs, the standards set a limit on the dose received, below which such effects would not be manifest. The limit given in the Radiation Protection Standards for an organ is the lower limit of that derived for stochastic effects and that derived for non-stochastic effects when that organ is the only irradiated organ. For purposes of radiation protection the limits given in the standards are specified in terms of annual dose-equivalent limits. For whole body exposure the annual limit for radiation workers is 50 mSv (or 50 000 µSv). In certain circumstances it is possible that only partial exposure of the body occurs or that single organ exposure occurs. In these circumstances limits are prescribed such that the risks associated with partial body exposure or with single organ exposure are the same as the risk with uniform whole body exposure. Accordingly higher limits are prescribed for these circumstances. When exposure is from external sources only the doses received can be determined by the use of personal monitors which give the doses received by the body at the point of wearing them. From the everyday point of view it is not convenient to determine from the monitor reading the dose to the whole body or to specific organs. In practice if the annual dose for an individual, as determined from the monitor results, does not exceed 50 mSv then the dose-equivalent limits for the whole body and for the various organs will not be exceeded provided the monitor has been worn on the body such that it would most likely have received the highest dose to the body.
  17. 17. 132 Although the standards prescribe limits on an annual basis only it is useful to ensure that doses reported for monitors do not exceed 1000 µSv per week (or 4000 µSv per four-weekly period). By this means it will become obvious during a year if there is any real likelihood of the annual limits either being approached or exceeded. In determining the total dose equivalent received from occupational exposure, exposures from normal natural background radiation or from radiological procedures to the individual (including radiodiagnosis, dentistry, radiotherapy and nuclear medicine) are not to be included. The standards make provision for special limits in circumstances involving planned special exposures. They recognise that limits cannot be set for emergency or accidental exposures, but that attempts must be made to assess as carefully and as quickly as possible the dose equivalents received in those situations so that any necessary remedial action can be taken. The Radiation Protection Standards do not make any special provision for females of reproductive capacity. However they state that when a pregnancy is confirmed (and this would normally be within a period of two months), arrangements should be made to ensure that the woman works only under such conditions that it is most unlikely that doses received during the remainder of the pregnancy would exceed three-tenths of the pro-rata annual dose-equivalent limits for occupationally exposed persons. The standards do not prescribe limits for individual members of the public. However they require that the design and operation of radiation facilities be such that, apart from radiation received by individuals undergoing radiological procedures, members of the public most likely to receive the highest dose from the sources, that is the critical group, are unlikely to receive more than one-tenth of the corresponding annual dose-equivalent limits for occupationally exposed persons. For whole body exposure for this group the annual dose-equivalent limit is 5 mSv provided the exposure does not occur over many years. If this should occur action should be taken to reduce radiation exposures so that in a lifetime, an average annual dose-equivalent limit of 1 mSv is not exceeded. References (1) National Health and Medical Research Council, Recommended radiation protection standards for individuals exposed to ionizing radiation, AGPS, Canberra, 1981 (2) ICRP (1977), Recommendations of the International Commission on Radiological Protection, Oxford, Pergamon Press, ICRP Publication 26 (Annals of the ICRP, Vol 1 No 3).
  18. 18. 133 ANNEXE IV PERSONAL MONITORING SERVICES WITHIN AUSTRALIA Personal monitoring services within Australia are operated by the following organisations: 1. Australian Radiation Laboratory. Telephone: (03) 433 2211 Lower Plenty Road, Yallambie, Vic. 3085. 2. Radiation Branch, Telephone: (02) 646 0222 Division of Occupational and Environmental Health Health Commission of New South Wales, Joseph Street, Lidcombe, N.S.W. 2141. 3. Division of Health and Medical Services, Telephone: (07) 224 5611 Department of Health, 535 Wickham Terrace, Brisbane, Qld. 4000 4. State X-Ray Laboratory, Telephone: (09) 380 1122 Verdun Street, ext. 2265 Nedlands, W.A. 6009 Users in other States should seek advice from their local statutory authority.
  19. 19. 134 ANNEXE V Ancillary equipment V.1 Special devices for radiography To position the animal correctly for radiography special devices should be used to reduce to an absolute minimum the number of occasions on which it is necessary for the animal to be held by hand. The following devices will be found useful: (a) Small animal radiography (i) Adhesive tape, gauze bandages Various types of tape and bandaging may be tied around, or placed over, an anatomical region to fix it in position for radiography. They may also be used to remove an overlying anatomical region from the area of interest. (ii) Sand bags The sand should be contained in a sealed bag with an outer cover that can be removed for cleaning. The bags should be made in a variety of sizes so that they can be placed over a limb, or used as a ‘prop’, to position an area for radiography. (iii) Positioning troughs These can be made of timber, perspex, or other sheet or foam plastic material. Usually, they are approximately V-shaped and may be constructed with adjustable sides. They are particularly useful for maintaining the animal in position for ventro-dorsal projections. (iv) Radiolucent pads Radiolucent pads, made from foam plastic or rubber, can be purchased in a variety of shapes and sizes and may be used to position the animal correctly. Plastic bags filled with cotton wool will serve the same function. (v) Cassette holders These may be simple devices, such as a welding clamp with a handle that can be attached to the cassette. Alternatively they may be of a 'picture-frame' design, permitting the cassette to be slipped into a frame, to which a handle is attached. Adjustable cassette holders which may be clamped to the edge of the examination table are very useful. A wall mounted cassette holder, adjustable in the vertical direction, can be used for standing lateral radiographs. (vi) Other devices The animal can also be positioned using compression bands (fitted to some X-ray tables), mouth gags, and suction cups that can be firmly fastened to the table (the cups may hold metal rods or padded metal plates that can be used to support the animal). Birds or small mammals may be restrained by placing them inside a short length of plastic tubing or piping with suitable ventilation. (b) Large animal radiography (i) Cassette holders In radiography of the distal limbs of standing animals, a cassette holder may be used that is of a design similar to that described for small animal radiography, provided the handle is of sufficient length to ensure that the hand and body of the user are outside the primary X-ray beam.
  20. 20. 135 A design of a cassette holder specially for large animal radiography is given in the following diagrams. In radiography of areas of the standing animal, other than the distal limb, the cassette should be placed either on a mobile stand that can be positioned beside the animal, or in a wall mounted cassette holder. (ii) Other devices Blocks of wood, including blocks for examination of the equine navicular bone, will be specially useful in positioning the hoof for radiography. In the anaesthetised animal, ropes and hobbles, and metal ‘props’ should be used to assist in positioning an area for radiography.
  23. 23. 138 ANNEXE VI PROCESSING OF EXPOSED RADIOGRAPHS Too great an emphasis cannot be placed on the need for high standards of practice in the processing of radiographs. Attention should be directed towards: • The organisation of the work in the darkroom to avoid damage to films. • The use of appropriate safe-lights for the type of film and the testing of them for light leakage. • The proper storage of unexposed film away from heat, radiation and chemical contamination. • The use of film on a first-in, first-out basis to minimize use of old stock. • The regular replenishment of processing solutions. • The procedures outlined below with respect to developing, fixing, washing and drying of films. High standards of processing contribute to better quality films for diagnostic purposes and to the elimination of one cause of avoidable, repeat radiographic examinations which result in additional unnecessary radiation exposure of the veterinary staff. The latent image produced on film during radiography is converted to a photographic image upon processing the film. Processing, in its simplest terms, consists of first developing the latent image on the film and then fixing the image by dissolving from the film those silver salts in the emulsion which were not affected by the X-ray beam. The proper processing of a satisfactorily exposed radiograph is a very important part of the procedure of radiography. It is relevant to note that the optimum quality with respect to detail and contrast of a radiograph cannot be achieved without proper processing. Unsatisfactory processing of an exposed film will result in a radiograph of less than optimal quality which may, on the one hand, lead to an incorrect diagnosis and, on the other, necessitate the repetition of the X-ray examination giving rise to unnecessary radiation exposure. In this context it is as well to observe that incorrect exposure technique in radiography cannot be compensated for by adjusting processing procedures. In addition a film which has been over-exposed and under-developed will not only be of less than optimal quality but will have been obtained with the animal and veterinary staff having received more radiation than is necessary. Although commercially available developing solutions contains a number of components directed towards providing the most desirable features of such a solution, the two main components are a potential developing agent (a chemical reducing agent) and an activator (an alkali) of this potential developing agent. The energy with which the developing action of a solution proceeds depends on the concentration of these important chemical components in the solution. With use, the concentration of the chemicals in the developing solution will change. The rate of change will partly depend on the number of films processed and on the age of the solutions. However due to oxidation the concentration of the reducing agent in a developing solution will decrease with time even when the solution is not used. The energy with which the developing action of a solution proceeds also varies with its temperature; the higher the temperature the more vigorous is the action. However temperatures which are too high will damage the emulsion whilst those that are too low will result in the developing action almost ceasing. The manufacturers of developing solutions make recommendations for optimal conditions of use of their solutions. This Code of Practice recommends that the procedures and practices laid down by the manufacturers are applied for the type of film being used. To obtain radiographs of a uniformly high quality it is important that exposed films be developed under reproducible conditions with respect to concentration of chemical components, temperature of solution and time of development and development techniques (that is manual or automatic techniques). Manufacturers of developing solutions will be able to recommend practices which may be adopted to compensate for the change of concentration of the chemical components of the solution with workload and time. With respect to the temperature-time relation, this Code of
  24. 24. 139 Practice recommends the use of a fixed temperature and fixed time of development unless an automatic processor is available, in which case these parameters are automatically controlled. If a fixed temperature is not achieved, it is important that the temperature of the developing solution be measured and a time of development employed appropriate to that temperature. Poor technique in fixing a film after development will result in a radiograph of less than optimal quality. If radiographs are to be retained for future reference it is important that the fixing action be complete and the film be subsequently thoroughly washed in running water. The manufacturer of fixing solutions can provide advice on the useful life of fixing solutions under various workloads. To obtain a satisfactory processed radiograph, the film should be adequately washed after the fixing stage and then dried under conditions which will not spoil the image.
  25. 25. 140 ANNEXE VII WARNING SIGNS Colours for the Warning Sign depicted below are: Background: Yellow Lettering and Trefoil: Black.