Code of Practice for the Safe Use ofIonizing Radiation in Veterinary Radiology

Reprinted from the Report of the 93rd Session of the Council, June 1982

© Commonwealth of Australia, 1983Australian Government Publishing Service, Canberra 1983

Printed by McCarron Bird, MelbourneR79/802(10)

The NHMRC has rescinded this publication in accordance with its policy of reviewing documentspublished more than 10 years ago. The NHMRC policy with regard to rescinded documents/publicationscan be found at www.nhmrc.gov.au. ARPANSA has taken over responsibility of the review process forthis publication. Continued use of publications is subject to the individual requirements of the relevantregulatory authority in each jurisdiction. The relevant authority should be consulted regarding the use ofthe advice contained in this publication. All publications in the Radiation Health Series will beprogressively reviewed by ARPANSA’s Radiation Health Committee and, where appropriate, will bere-published as part of the ARPANSA Radiation Protection Series. Enquiries about the Radiation HealthSeries publications should be forwarded to the ARPANSA Standards Development and CommitteeSupport Section, 619 Lower Plenty Road, Yallambie, Victoria, 3085. Tel: 03 9433 2211, Fax:03 9433 2353, Email: secretariat@arpansa.gov.au.

117

Appendix XXI Code of practice for the safe use of ionizingradiation in veterinary radiology

CONTENTS

Part I - General

Section 1 - Introduction

1.1 Need for this Code1.2 Scope of this Code1.3 Application of this Code1.4 Dose limits1.5 Categories of exposed persons1.6 Risk of radiation injury1.7 Specialised meanings for ‘shall’ and ‘should’

Section 2 - Responsibilities and Radiation Surveillance

2.1 Overall responsibility2.2 Responsibility of User for radiation protection2.3 Legislative requirements2.4 Designation of radiation workers2.5 Personal monitoring2.6 Radiation monitoring records2.7 Radiation surveys

Part II - Diagnostic Radiology

Section 3 - Procedures and Facilities

3.1 Introduction3.2 Facilities - General3.3 Radiography in defined X-ray rooms or areas3.4 Reduction of radiation hazards3.5 Restraint of animals3.6 Radiography outside defined X-ray rooms or areas3.7 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

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 inteaching and research. Whenever these radiations are used on animals, there isconsiderable potential for persons involved in such practices to be exposed to theradiation hazards that could arise from them. Guidance is therefore needed on theprotective measures and procedures that should be adopted to ensure, first, that anylimits prescribed with respect to exposure of persons are not exceeded, and second, thatsuch 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. Thecode is in three parts:

Part I GeneralPart II Diagnostic RadiologyPart III RadiotherapyNote: 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 inAustralia and implemented by the appropriate statutory authorities (see Annexe I).Advice on this legislation and on any aspects of the implementation of this code shouldbe sought from these authorities. This code is intended as a guide to safe practices andshould be applied with sound judgement to specific situations. It is recommended thatestablishments draw up their own detailed working procedures based on the relevantlegislation and this code, and that they issue appropriate instructions to all workers whomay 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 respectto exposure of persons will not be exceeded and that any unnecessary exposure will beminimised.

1.4 Dose limits

Radiation doses greatly exceeding those normally received from natural backgroundradiation are known to cause harm and in particular to increase the risk of cancer. It isnot known, however, if harmful effects are induced at low doses and low dose rateswhich are comparable to or slightly in excess of those of background radiation. Becauseof this, it is cautiously assumed that any exposure to radiation may entail some risk andthat 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 radioactivesubstances are chosen so that the risks arising from the average doses received in thatwork are no greater than risks in other occupations that have high standards of safety.

119

Likewise, limits of radiation dose for the public are chosen so that the risks to them areno greater than other risks considered acceptable in everyday life. The doses chosen tolimit the risks forma set of dose limits.

Dose limits are applied in operations involving radiation and radioactive substances toensure that the upper limits of the risks to health of the exposed persons and of societyare appropriately small. They have been prepared as Radiation Protection Standards forthe National Health and Medical Research Council, which has published them inRecommended radiation protection standards for individuals exposed to ionizing radiation (seeAnnexe II). Council has recommended that these Standards be used throughoutAustralia.

Background information on the biological effects of ionizing radiations and a summaryof the dose limits given in these Standards are in Annexe III. Further advice oninterpretation and application of the Standards and dose limits is available from theappropriate 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 beexposed to ionizing radiation arising from their direct involvement with sources ofsuch radiation, and

(b) members of the public.

Radiation workers include all members of a department or practice, including temporaryor visiting staff whose duties are likely to require their presence during radiographic andradiotherapeutic 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 forradiography, etc.

1.6 Risk of radiation injury

If the provisions of this code are applied carefully and consistently, the dose limits willnot be exceeded and the risk of radiation injury will be slight. However, if the dose limitslaid down in the Radiation Protection Standards are exceeded by a large factor in a singleexposure or in a number of exposures over a short period of time, or are exceeded over along period, injury may result. Attention is drawn to the manner in which the dose limitsmay be exceeded in relation to the veterinary practice.

1.6.1 In radiography, the principal hazard arises from the possibility of exposure tothe primary X-ray beam. Scattered radiation and radiation leaking from the X-raytube assembly, which are always present during an exposure, may also contributefurther significant doses.

1.6.2 In radiotherapy, the radiation dose delivered to the patient is very much greaterthan in diagnostic procedures and thus the potential hazard may be very muchgreater to the operator.

1.7 Specialised meanings for ‘shall’ and ‘should’

The words ‘shall’ and ‘should’ and ‘should’, where used in this Code have specialisedmeanings. ‘Shall’ indicates that the particular requirement is mandatory. ‘Should’indicates a requirement that is to be applied as far as practicable, in the interest ofreducing radiation risks.

120

Section 2 - Responsibilities and Radiation Surveillance

2.1 Overall responsibility

The responsibility for radiation protection lies with the person in control of theinstitution, department or practice using the X-ray equipment and/or radioactivesubstances. This person is referred to as the User for the purposes of this Code. In somecircumstances the User may appoint a Radiation Safety Officer to act for him. The Useror Radiation Safety Officer shall have the authority and sufficient professional ortechnical 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/orequipment 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 appropriatestatutory authority including registration, licensing, monitoring, recording of personaldoses, 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' undersubclause 1.5(a). This shall include all veterinary surgeons, veterinary nurses, and otherswho 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 radiationworker shall be monitored in accordance with the requirements of the statutoryauthority. If personal monitoring is required, monitors should be worn on thebody at chest or waist height during the period of occupational exposure. Whenlead protective aprons are worn, monitors should be worn under the aprons. Insome cases it may also be necessary to measure the dose to other parts of thebody, for example to the hands and forearms, so as to ascertain that the relevantdose-equivalent limits are not exceeded. (Personal monitors can be obtainedfrom the Radiation Monitoring Services listed in Annexe IV.)

2.5.2 It may be advisable for visitors or other staff, who occasionally enter areasnormally occupied by radiation workers, to wear monitors during theiroccupancy of such areas so that the radiation levels to which such persons areexposed 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 workeras required by the statutory authority. They shall show any doses received duringthe present period of employment and also doses received as a result of previousemployment in which ionizing radiations were used. Radiation dose recordsprovide information on the doses received and indicate the efficacy of the safetyprocedures that have been implemented. They shall be available for inspectionby the individual workers concerned and the statutory authority.

2.6.2 When an employee is first designated as a 'radiation worker' his employer shallrequest from the employee's previous employer a copy of the radiation doserecord for that employee.

121

2.7 Radiation surveys

2.7.1 Plans for buildings that are to incorporate radiographic or radiotherapeuticfacilities shall be submitted to the statutory authority.

2.7.2 The User in consultation with the statutory authority shall ensure thatappropriate radiation safety assessments are made. These will be required in thefollowing circumstances:

(a) Before the installation is put into routine use.

(b) If the installation or working procedures are modified. 'Modified' means achange in the amount of radiation, the manner of its use or a change in theX-ray equipment or its location. Such modifications may mean the originalprotection 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 higherthan normal for no obvious reason, or are significantly higher than averagedoses received in similar departments and practices.

(d) If changes are made in the immediate environs, for example a store or waitingarea 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 inexcess of the appropriate dose-equivalent limits, the User shall notify thestatutory authority.

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 theprocedure and if it can be performed without undue radiation hazard.

3.1.2 Radiography shall be carried out only by appropriately trained and qualifiedpersonnel.

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 beamunless it is adequately shielded by protective clothing (see 3.2.7). Fluoroscopyshall 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 duringradiographic and fluoroscopic examinations. These persons shall be properlyinstructed and should understand their part in the proposed procedure. All suchpersons shall position themselves behind protective screens, except where this isnot practicable, in which case they shall wear protective aprons and remain as faras practicable from the primary X-ray beam, the animal and the X-ray tubeassembly.

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 portableX-ray machine is taken to the animal.

3.2.2 X-ray machines shall have sufficient capacity to provide radiographs of gooddiagnostic quality. In addition, adequate facilities to provide control over theanimal and protection of the operator are necessary. As these are best providedin a defined X-ray room or area, radiography outside such areas shall be carriedout 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 followingAustralian Standards and with any variations or additions required by theappropriate statutory authority.

AS 2398 -1980 Fixed Diagnostic X-Ray Equipment - Design, Constructionand 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 therequirements should be obtained from the appropriate statutory authority. Testsfor compliance shall be carried out at regular intervals in accordance withrequirements of the statutory authority.

123

3.2.4 An examination table shall be provided with either protective shieldingequivalent to 0.5 mm lead on the sides or with protective shielding equivalent to1 mm lead underneath the table top and any Potter-Bucky diaphragmincorporated in the table. For ease of cleaning and to prevent mechanicaldamage the lead shielding should be covered with laminated plastic sheeting.

3.2.5 Sand bags, v-troughs, slings, adhesive tape or other positioning and immobilisingdevices shall be available for supporting the animal during radiography (seeAnnexe V).

3.2.6 Suitable cassette holders shall be available for use when using horizontal orangled X-ray beams. If they are not self supporting, they shall be fitted withhandles at least 1 metre long and a ground support to ensure that a personholding 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 asaprons, gloves and shields suitable for hand and forearm, shall be provided forall persons who are required to be present during radiography and who are notprotected by fixed or mobile protective screens. Such protective devices shallhave a lead-equivalent thickness throughout of not less than 0.25 millimetre, andof not less than 0.5 millimetre when energies above 100 kV peak are used. Theselead protective devices shall be examined both visually and radiographically on aregular basis (e.g. three-monthly for a practice with a heavy X-ray work load) toensure that their shielding efficiency has not become impaired by cracks due tosharp 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 therequired radiographic examination.

3.3.2 All small animal radiography should be carried out in a defined X-ray room orarea.

3.3.3 Advice on all shielding requirements for defined X-ray rooms or areas should beobtained from the appropriate statutory authority. However, the need forstructural shielding is reduced by, whenever possible, directing the X-ray beamvertically down with the animal placed on an X-ray table. Single clay brick wallsor equivalent normally afford adequate protection for adjoining areas. Forhorizontal 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 theproducts obtained by multiplying the X-ray tube current by the time for eachexposure during that period. If the X-ray work load exceeds 2000 milliampereseconds per week a protective screen incorporating a viewing window ofprotective glass shall be provided between the operator and the X-ray tubeassembly. Such a screen should be at least 2 metres high and at least 1 metrewide. The lead equivalent of the screen, including the window, shall be not lessthan 0.5 millimetre and the lead or other protective material in the screen shall

124

adequately overlap at any joins and around the viewing window. Advice onscreen 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 ofradiographs.

(b) Ensuring that the primary beam is restricted to the area to be examined bymeans of the collimator.

(c) Using the fastest film and film-intensifying screen combination compatiblewith 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 beundertaken and understand their part in it.

(f) Ensuring that all assistants remain behind the protective screens, or if there isno screen, wear protective clothing and position themselves as far aspracticable from the X-ray tube assembly, the animal and the path of theprimary X-ray beam.

(g) Ensuring that the exposure is not made until the animal is properly restrainedand positioned.

(h) Ensuring that appropriate film processing facilities are available and are usedcorrectly. (See Annexe VI).

3.4.2 Cassette holders shall be used whenever a cassette cannot be supported on atable, on the ground or on another support. A person supporting a cassetteholder 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 whichprovides adequate stability and does not allow movement blurring of theradiograph.

3.4.4 Routine working procedures for radiography shall be devised. The proceduresshall be appropriate to the type of work carried out in the establishment andshall include appropriate precautions to reduce radiation exposure, positioningrequirements for animals and exposure techniques. They shall be followed bypersons carrying out and assisting with radiography and shall be posted in theX-ray areas.

3.4.5 Reference should be made also to Australian Standard AS -"Guide to goodradiological practices" (in preparation).

3.5 Restraint of animals

3.5.1 The animal shall not be held for radiography unless for clinical reasons othermeans of immobilisation are not practicable. Immobilisation should be achievedby mechanical means, by tranquillisation or by anaesthesia. These methods willeliminate or reduce the radiation hazard from manual restraint and assist in thereduction of image blurring due to movement. Advice on mechanical restraintsis given in Annexe V.

3.5.2 When, in exceptional circumstances, manual restraint is necessary, the followingprocedures shall be adopted:

(a) The animal shall be restrained by the minimum number of persons necessary.

125

(b) All persons shall position themselves as far as practicable from the path of theprimary X-ray beam, the animal and the X-ray tube housing. No part of anyperson 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 ionizingradiation (for instance the owners of the animal) may be asked to hold theanimal, provided that any reduction in control that results will notsignificantly increase the radiation hazard of the procedure. Children andpregnant women shall not hold animals during radiography and a notice tothis effect shall be displayed prominently in the X-ray area.

(e) When it is necessary for staff to hold an animal during radiography, oneindividual should not be asked to hold an animal repeatedly. Pregnant staffmembers should not hold animals during radiography.

3.5.3 The radiography of large animals, e.g. horses and cattle, creates additionalproblems in relation to radiation hazards for the following reasons:

(a) It is seldom practicable to anaesthetise the animal and some form of manualrestraint 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. Thusthere is a greater risk of irradiating assistants.

(d) Those who restrain the animal or support the cassette holder are more likelyto have their attention concentrated on their task rather than on avoiding theuseful beam.

(e) Radiography of regions other than the lower limbs requires the use ofconsiderably greater exposure factors that will increase the hazard both fromthe primary beam and from scattered radiation. Such examinations should becarried 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 thelight levels out of doors and in such circumstances there is a tendency toincrease the area of the X-ray beam to an excessive size. From this point ofview, it is preferable for outdoor radiography to be done in the shade. If alight beam collimator is not provided with an indication of the beam size atthe various focus-film distances used, or if the illumination is inadequate,additional cones or aperture diaphragms shall be used during outdoorradiography to restrict the beam to the size of the X-ray film used. Each coneshall 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, thereis a particular responsibility to ensure that, despite all difficulties, all precautionsare observed. The following precautions shall be taken:

(a) The animal should be suitably tranquillised or anaesthetised wheneverpossible prior to radiography.

(b) All assistants shall wear sufficient protective clothing to give full protectionfrom the source of radiation (for example, it may be necessary to protect thelegs).

(c) All assistants not immediately required for the procedure shall remain at a safedistance.

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 ofthe premises, or on visits to farms, stables or kennels) is likely to add to theradiation 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 unauthorisedpersons 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 carefullyexplained to the assistants before the radiographic exposures are made.

(e) Adequate precautions are taken to prohibit the access of unauthorisedpersons to the area during radiography (e.g. by display of warning signs - seeAnnexe VII).

(f) The dose to members of the public, i.e. persons passing by or in adjoiningrooms or areas, is limited.

(g) Adequate supports for the X-ray tube assembly and cassettes are provided. Inno 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 thecassette and to ensure that the X-ray beam is collimated to an area equal to orless than the cassette (see 3.5.3 (f)).

3.7 Fluoroscopic procedures

3.7.1 Fluoroscopy is potentially more hazardous than radiography, because theproduct of exposure time and X-ray tube current is usually greater in the formerand 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 canbe seen radiographically, the additional risks of using fluoroscopy as a substitutefor radiography cannot be justified. Fluoroscopy is indicated only incircumstances in which it is essential to study movement. When indications aresufficiently definite for fluoroscopy, it shall be carried out only if suitableequipment is available and by veterinary or medical personnel trained andexperienced in this technique.

3.7.2 An X-ray image intensification system shall be used. It shall be properly installedand subject to service and maintenance at least once per year. A remotetelevision 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 offluoroscopy may require special approval from the statutory authority.

127

ANNEXE I STATUTORY AUTHORITIES WITHIN AUSTRALIA

In parts of this code, reference is made to the appropriate statutory authority. The appropriatecontacts for matters relating to the statutory requirements of the authorities in the States andTerritories are:

1. AUSTRALIAN CAPITAL TERRITORY

Consultant, Radiation Safety Telephone: (062) 43 2111Capital Territory Health CommissionP.O. Box 825Canberra City, A.C.T. 2601

2. NEW SOUTH WALES

Officer-in-Charge Telephone: (02) 646 0222Radiation BranchDivision of Occupational and Environmental HealthHealth Commission of N.S.W.P.O. Box 163Lidcombe, N.S.W. 2141

3. NORTHERN TERRITORY

Physicist Telephone: (089) 80 2911Occupational Health BranchN.T. Department of HealthP.O. Box 1701Darwin, N.T. 5794

4. QUEENSLAND

Director Telephone: (07) 224 5611Division of Health and Medical PhysicsDepartment of Health535 Wickham TerraceBrisbane, Qld 4000

5. SOUTH AUSTRALIA

Senior Health Physicist Telephone: (08) 218 3211Occupational Health and Radiation Control BranchSouth Australian Health CommissionG.P.O. Box 1313Adelaide, S.A. 5001

6. TASMANIA

Health Physicist Telephone: (002) 30 6421Division of Public HealthDepartment of Health ServicesP.O. Box 191BHobart, Tas. 7001

7. VICTORIA

Senior Scientific Officer Telephone: (03) 616 7777Occupational Health ServicesHealth Commission of Victoria555 Collins StreetMelbourne, Vic. 3000

128

8. WESTERN AUSTRALIA

The Secretary Telephone: (09) 380 1122Radiological CouncilState X-ray LaboratoryDepartment of Public HealthVerdun StreetNedlands, W.A. 6009

129

ANNEXE II BIBLIOGRAPHY

1. National Health and Medical Research Council Recommended radiation protection standards forindividuals 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 - safetyrequirements

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 ofAustralia

NEW SOUTH WALES80 Arthur Street WESTERN AUSTRALIANorth Sydney 2060 11-13 Lucknow PlaceTelephone: 929 6022 West Perth 6005Telex: 26514 Telephone: 321 7763Telegrams: Austandard,North Sydney TASMANIA

18 Elizabeth Street51 King Street Hobart 7000Newcastle 2300 Telephone: 34 6911Telephone: 2 2477

VICTORIAQUEENSLAND 191 Royal Parade447 Upper Edward Street Parkville 3052Brisbane 4000 Telephone: 347 7911Telephone: 221 8605 Telex: 33877

SOUTH AUSTRALIA NORTHERN TERRITORY11 Bagot Street C/- Master Builders AssociationNorth Adelaide 5006 191 Sturt HighwayTelephone: 267 1757 Darwin 5790

Telephone: 81 9666

130

ANNEXE III BIOLOGICAL EFFECTS OF IONIZINGRADIATION AND LIMITS IN EXPOSURE TO SUCHRADIATION.

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 threedecades, on the possible biological effects of ionizing radiation on man. These effects may manifestthemselves in the exposed individual and they are then referred to as somatic effects or they mayarise in the descendants of the exposed individual, in which case they are referred to as hereditaryeffects. It is important to recognise, however, that many of the biological effects that can be causedby ionizing radiation may also result from exposure to other agents and it is not always possible todetermine the cause of an effect.

Man has always been exposed to radiation, and this arises from terrestrial sources, cosmic radiationand radionuclides deposited in the body. This natural background radiation varies from place toplace 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 thanelsewhere. The levels of exposure from this radiation are such that it is not possible to ascribe anyof the ill-effects in man specifically to this radiation. On the other hand, radiation-induced effectshave been observed in man when individuals have been exposed to very large radiation doses and itis 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 aresult of using radium luminous compounds for painting dials on watches and instruments, manyworkers developed bone sarcoma; some miners working in uranium mines developed lung cancer;some radiologists developed skin erythema and leukaemia when not using adequate radiationprotection; and there was a small excess of leukaemia and other malignant diseases above theexpected incidence rates among survivors of the atomic bombs in Hiroshima and Nagasaki in Japanfollowing exposure to radiation. In all the above examples, and there are many more demonstratedradiation-induced effects, the doses received by individuals were very large - many times the dosearising from natural background radiation.

The effects arising from large radiation doses are well known and many studies have beenundertaken in order to correlate radiation-induced effects with smaller doses. However, it has notbeen possible to confirm that the incidence of effects is directly related to the doses received as thestatistics available for such studies have been inadequate. Accordingly studies have been carried outon animals and plants to determine if there is any correlation with them between effects and dosedelivered and dose rate. It has been shown that the incidence of many biological effects produced isrelated to the total dose delivered, whilst for other effects, there appear to be threshold doses belowwhich those effects may not occur. Whilst it is not possible in all cases to extrapolate the results ofthese studies to man, they serve a very useful purpose in identifying possible dose-effectrelationships.

The effects arising from exposure to ionizing radiation fall into two categories. Stochastic effectsare those for which the probability of an effect but not the severity of the effect occurring isregarded as a function of the dose to which the individual is exposed. It is considered that there isno threshold dose below which the probability of such an effect occurring is zero. On the otherhand, non-stochastic effects are those for which the severity of the effect varies with the dose towhich the individual is exposed and a threshold may occur, below which such an effect does notoccur.

From the studies undertaken, it is known that the induction of malignancies, including leukaemia isa stochastic effect of radiation, although such malignancies may not become manifest until manyyears after the radiation exposure. Mutagenic effects are also stochastic effects and these may bepropagated 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.

131

only likely to become apparent in the first or second generation following irradiation of anindividual. A defect causing slight physical or functional impairment, and which may not even bedetectable, will tend to continue in the descendants, whereas a severe defect will be eliminatedrapidly through the early death of the zygote or of the individual carrying the defective gene. Therisk of mutagenic effects arising will decrease with increasing age of the irradiated individuals due totheir decreasing child expectancies with age.

Non-stochastic effects arising are specific to particular tissues, for example, non-malignant damageto the skin, cataract of the eye, gonadal cell damage leading to impaired fertility etc. For many ofthese effects a minimum or threshold dose may be required for the effect to be manifest. If anindividual receives a dose greatly in excess of the threshold dose the manifestation of the effect willoccur in a relatively short period after the irradiation. However if the dose is not greatly in excess ofthe threshold dose many of the resulting effects will be of a temporary nature and reversion tonormal conditions usually occurs.

From our knowledge of biological effects arising from exposure to radiation, it is possible toidentify the risks of stochastic effects occurring with the doses received by the various organs andtissues of the body. These risks are derived from exposure of persons to very high doses and fromstudies on animals etc. As there is very little information on the effects of exposure to low doses itis cautiously assumed that risk is directly proportional to dose, right down to zero dose and thatthere is no threshold below which these effects do not occur. These assumptions may lead tooverestimates of the risks associated with exposure to low doses of radiation. Although the risksderived from such assumptions may be very small, it is important that they are kept small byensuring that all radiation exposure of individuals is kept As Low As Reasonably Achievable (referredto 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 radiationpractices as well as with the protection of members of the public. It recognises that variouspractices involving radiation exposure are necessary for the well-being of individuals and for thegood of mankind. In undertaking such practices, individuals as radiation workers or as members ofthe public, may be irradiated and the exposure resulting from those practices must be minimised inaccordance with the ALARA principle. Good radiation protection practice requires the setting ofstandards of occupational exposure and these are such that the risk of fatalities arising fromradiation-induced malignancies from the average doses received in such exposure is no greater thanthe risk of fatalities arising in other occupations that have high standards of safety. RadiationProtection 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 onRadiological Protection (2). They assume for stochastic effects a linear relationship between riskand dose and that there is no threshold dose below which effects do not occur. For non-stochasticeffects relating to specific organs, the standards set a limit on the dose received, below which sucheffects would not be manifest. The limit given in the Radiation Protection Standards for an organ isthe lower limit of that derived for stochastic effects and that derived for non-stochastic effectswhen that organ is the only irradiated organ.

For purposes of radiation protection the limits given in the standards are specified in terms ofannual dose-equivalent limits. For whole body exposure the annual limit for radiation workers is50 mSv (or 50 000 µSv). In certain circumstances it is possible that only partial exposure of thebody occurs or that single organ exposure occurs. In these circumstances limits are prescribed suchthat the risks associated with partial body exposure or with single organ exposure are the same asthe risk with uniform whole body exposure. Accordingly higher limits are prescribed for thesecircumstances.

When exposure is from external sources only the doses received can be determined by the use ofpersonal monitors which give the doses received by the body at the point of wearing them. Fromthe everyday point of view it is not convenient to determine from the monitor reading the dose tothe whole body or to specific organs. In practice if the annual dose for an individual, as determinedfrom the monitor results, does not exceed 50 mSv then the dose-equivalent limits for the wholebody and for the various organs will not be exceeded provided the monitor has been worn on thebody such that it would most likely have received the highest dose to the body.

132

Although the standards prescribe limits on an annual basis only it is useful to ensure that dosesreported for monitors do not exceed 1000 µSv per week (or 4000 µSv per four-weekly period). Bythis means it will become obvious during a year if there is any real likelihood of the annual limitseither being approached or exceeded.

In determining the total dose equivalent received from occupational exposure, exposures fromnormal natural background radiation or from radiological procedures to the individual (includingradiodiagnosis, dentistry, radiotherapy and nuclear medicine) are not to be included. The standardsmake provision for special limits in circumstances involving planned special exposures. Theyrecognise that limits cannot be set for emergency or accidental exposures, but that attempts mustbe made to assess as carefully and as quickly as possible the dose equivalents received in thosesituations so that any necessary remedial action can be taken.

The Radiation Protection Standards do not make any special provision for females of reproductivecapacity. However they state that when a pregnancy is confirmed (and this would normally bewithin a period of two months), arrangements should be made to ensure that the woman worksonly under such conditions that it is most unlikely that doses received during the remainder of thepregnancy would exceed three-tenths of the pro-rata annual dose-equivalent limits foroccupationally exposed persons.

The standards do not prescribe limits for individual members of the public. However they requirethat the design and operation of radiation facilities be such that, apart from radiation received byindividuals undergoing radiological procedures, members of the public most likely to receive thehighest dose from the sources, that is the critical group, are unlikely to receive more than one-tenthof the corresponding annual dose-equivalent limits for occupationally exposed persons. For wholebody exposure for this group the annual dose-equivalent limit is 5 mSv provided the exposure doesnot occur over many years. If this should occur action should be taken to reduce radiationexposures 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 forindividuals 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).

133

ANNEXE IV PERSONAL MONITORING SERVICES WITHINAUSTRALIA

Personal monitoring services within Australia are operated by the following organisations:

1. Australian Radiation Laboratory. Telephone: (03) 433 2211Lower Plenty Road,Yallambie, Vic. 3085.

2. Radiation Branch, Telephone: (02) 646 0222Division of Occupational and

Environmental HealthHealth Commission of New South Wales,Joseph Street,Lidcombe, N.S.W. 2141.

3. Division of Health and Medical Services, Telephone: (07) 224 5611Department of Health,535 Wickham Terrace,Brisbane, Qld. 4000

4. State X-Ray Laboratory, Telephone: (09) 380 1122Verdun Street, ext. 2265Nedlands, W.A. 6009

Users in other States should seek advice from their local statutory authority.

134

ANNEXE V Ancillary equipment

V.1 Special devices for radiography

To position the animal correctly for radiography special devices should be used to reduceto an absolute minimum the number of occasions on which it is necessary for the animal tobe 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, ananatomical region to fix it in position for radiography. They may also be used toremove 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 beremoved for cleaning. The bags should be made in a variety of sizes so thatthey can be placed over a limb, or used as a ‘prop’, to position an area forradiography.

(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 withadjustable sides. They are particularly useful for maintaining the animal inposition for ventro-dorsal projections.

(iv) Radiolucent pads

Radiolucent pads, made from foam plastic or rubber, can be purchased in avariety 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 beattached 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 theexamination table are very useful. A wall mounted cassette holder, adjustable inthe vertical direction, can be used for standing lateral radiographs.

(vi) Other devices

The animal can also be positioned using compression bands (fitted to someX-ray tables), mouth gags, and suction cups that can be firmly fastened to thetable (the cups may hold metal rods or padded metal plates that can be used tosupport the animal). Birds or small mammals may be restrained by placing theminside 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 beused 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 ofthe user are outside the primary X-ray beam.

135

A design of a cassette holder specially for large animal radiography is given inthe following diagrams.

In radiography of areas of the standing animal, other than the distal limb, thecassette should be placed either on a mobile stand that can be positioned besidethe 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 theanaesthetised animal, ropes and hobbles, and metal ‘props’ should be used toassist in positioning an area for radiography.

136

VETERINARY RADIOGRAPHY CASSETTE HOLDER FOR LARGE ANIMALS

137

VETERINARY RADIOGRAPHY CASSETTE HOLDER FOR LARGE ANIMALS

Rear view

Plan view

Lateral view

138

ANNEXE VI PROCESSING OF EXPOSED RADIOGRAPHS

Too great an emphasis cannot be placed on the need for high standards of practice in theprocessing 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 lightleakage.

• 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 offilms.

High standards of processing contribute to better quality films for diagnostic purposes and to theelimination of one cause of avoidable, repeat radiographic examinations which result in additionalunnecessary radiation exposure of the veterinary staff. The latent image produced on film duringradiography is converted to a photographic image upon processing the film. Processing, in itssimplest terms, consists of first developing the latent image on the film and then fixing the imageby dissolving from the film those silver salts in the emulsion which were not affected by the X-raybeam. The proper processing of a satisfactorily exposed radiograph is a very important part of theprocedure of radiography. It is relevant to note that the optimum quality with respect to detail andcontrast of a radiograph cannot be achieved without proper processing. Unsatisfactory processingof an exposed film will result in a radiograph of less than optimal quality which may, on the onehand, lead to an incorrect diagnosis and, on the other, necessitate the repetition of the X-rayexamination giving rise to unnecessary radiation exposure. In this context it is as well to observethat incorrect exposure technique in radiography cannot be compensated for by adjustingprocessing procedures. In addition a film which has been over-exposed and under-developed willnot only be of less than optimal quality but will have been obtained with the animal and veterinarystaff having received more radiation than is necessary.

Although commercially available developing solutions contains a number of components directedtowards providing the most desirable features of such a solution, the two main components are apotential developing agent (a chemical reducing agent) and an activator (an alkali) of this potentialdeveloping agent. The energy with which the developing action of a solution proceeds depends onthe concentration of these important chemical components in the solution. With use, theconcentration of the chemicals in the developing solution will change. The rate of change will partlydepend on the number of films processed and on the age of the solutions. However due tooxidation the concentration of the reducing agent in a developing solution will decrease with timeeven when the solution is not used.

The energy with which the developing action of a solution proceeds also varies with itstemperature; the higher the temperature the more vigorous is the action. However temperatureswhich are too high will damage the emulsion whilst those that are too low will result in thedeveloping action almost ceasing. The manufacturers of developing solutions makerecommendations for optimal conditions of use of their solutions. This Code of Practicerecommends that the procedures and practices laid down by the manufacturers are applied for thetype of film being used.

To obtain radiographs of a uniformly high quality it is important that exposed films be developedunder reproducible conditions with respect to concentration of chemical components, temperatureof solution and time of development and development techniques (that is manual or automatictechniques). Manufacturers of developing solutions will be able to recommend practices which maybe adopted to compensate for the change of concentration of the chemical components of thesolution with workload and time. With respect to the temperature-time relation, this Code of

139

Practice recommends the use of a fixed temperature and fixed time of development unless anautomatic processor is available, in which case these parameters are automatically controlled. If afixed temperature is not achieved, it is important that the temperature of the developing solution bemeasured and a time of development employed appropriate to that temperature. Poor technique infixing a film after development will result in a radiograph of less than optimal quality. Ifradiographs are to be retained for future reference it is important that the fixing action be completeand the film be subsequently thoroughly washed in running water. The manufacturer of fixingsolutions 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 fixingstage and then dried under conditions which will not spoil the image.

140

ANNEXE VII WARNING SIGNS

Colours for the Warning Sign depicted below are:

Background: YellowLettering and Trefoil: Black.