CODE OF SAFE PRACTICE FOR THE USE OF X-RAYS IN PODIATRY
Office of Radiation Safety P O Box 3877
Revised June 2010
? Office of Radiation Safety
Ministry of Health
Published with the permission of the Director-General of Health
1 INTRODUCTION 1
2 PROTECTION OF THE PATIENT 1
2.1 Clinical and administrative aspects 1
2.2 Protection of the gonads 2
3 PROTECTION OF PERSONNEL 3
3.1 Protection of non-radiation personnel 3
3.2 Protection of operator at the x-ray controls 4
3.3 Protection from exposure to the useful x-ray beam
while holding patients or image receptors in position
during radiography 4
4 X-RAY EQUIPMENT 5
4.1 Appropriate x-ray equipment 5
4.2 Efficient performance of x-ray machines 6
4.3 Light beam diaphragm 7
4.4 Filtration in the x-ray beam 7
4.5 Source-skin distance 8
4.6 X-ray exposure device 8
4.7 Leakage radiation 9
4.8 X-ray films and intensifying screens 9
4.9 X-ray film processing 10
5 ORGANISATION AND ADMINISTRATION OF
RADIATION PROTECTION 10
5.1 Personnel monitoring 10
5.2 Radiation protection surveillance 11
5.3 Dose limits for occupational exposure 11 6 RADIATION PROTECTION LEGISLATION AND
RESPONSIBILITIES OF LICENSEES 12
6.1 Radiation Protection Act 1965 12 7 BIBLIOGRAPHY 14
1.1 The purpose of this Code is to provide criteria for working procedures, x-ray equipment and protective materials necessary for the use of x-rays in podiatric diagnosis according to currently accepted standards of safety. Conformity with this Code may be taken as a primary indication of compliance with radiation protection legislation.
1.2 A copy of this Code is provided to all licensees in podiatric radiography. Licensees shall provide free and convenient access to this Code to all persons using x-ray equipment under their control.
1.3 This Code is compatible with the Recommendations of the International Commission on Radiological Protection (ICRP). Relevant ICRP publications are listed in the bibliography.
1.4 Throughout this Code, measures which are considered necessary for the achievement of satisfactory protection are denoted by the imperative shall and
those which are desirable protective measures by should.
2 PROTECTION OF THE PATIENT
2.1 Clinical and administrative aspects
2.1.1 A basic principle of protection in diagnostic radiology is that an x-ray examination should not be performed unless the benefits accruing to the patient outweigh any radiation risks. Judgement of whether benefits outweigh risks may reasonably be possible in cases where the potential radiation injury is the result of acute excessive doses where the effects are observed in the short term. However, the estimates of risks of delayed injury, such as carcinogenesis, resulting from chronic exposure at the low radiation dose levels typical of most diagnostic radiology are derived from epidemiological studies and can be expressed only on a statistical basis. The simpler question of whether the x-ray examination is necessary for adequate diagnosis should always be examined. In many cases
examinations may routinely be requested to exclude the possibility of unexpected causes or conditions and not be based on clear-cut clinical indications. Implicitly the diagnosis provided by podiatric radiography determines subsequent patient management. If management is expected to be unaffected by the result of an x-ray examination then the need for the examination may be questioned.
2.1.2 Radiological evidence has demonstrated that certain tissues such as the red marrow, gonads, breast (female), lungs, thyroid and bone surfaces may be particularly sensitive to radiation. The total effect of a given dose depends significantly also on the extent of irradiation of other tissues. An expression of the total effect delivered in a diagnostic x-ray examination is the Effective Dose Equivalent, H, which is the sum of the doses to the above specified E
organs and other organs, weighted according to their relative radiosensitivities. For podiatric radiography the effective dose equivalent will be lower than for most diagnostic x-ray procedures because only the bone surfaces amongst the specified organs are included, and no other organs of significant radiosensitivity.
The effective dose equivalent would increase considerably if in any podiatric procedure the x-ray beam were directed towards the lower abdominal region. The longer life expectancy of children results in a greater potential for the manifestation of possible deleterious effects of radiation. Children may also be more radiosensitive. Therefore particular attention should be given to minimising doses to children and indeed, whether the examination is essential. 2.1.3 The useful x-ray beam should be restricted to the area of clinical
interest and shall be collimated to within the cross section of the x-ray film cassette.
2.1.4 Some methods of dose reduction (such as minimising areas of x-ray fields on the patient) also cause improvement of image quality. However, many dose reduction methods act to the detriment of image quality (eg, use of high-speed rather than par-speed screens decreases doses but increases graininess in the image). A compromise between the opposing objectives to minimise doses and to produce good quality images, must therefore eventually be reached.
2.2 Protection of the gonads
2.2.1 Irradiation of the testes and ovaries shall be minimised.
2.2.2 As far as it is possible the useful x-ray bean shall not be directed
towards the pelvic and lower abdominal regions of patients. Where a special angulation is needed which would not comply with this requirement, a leaded apron or other suitable shield shall be draped over the pelvis of the patient or
Note: Compared with the amounts of radiation reaching the foetus or ovaries in the case of direct useful beam irradiation of the abdomen, the scattered radiation reaching these organs during irradiation of other parts of the body is small. This is particularly true when only the feet and ankles are irradiated.
3 PROTECTION OF PERSONNEL
3.1 Protection of non-radiation personnel
3.1.1 Persons who are not radiation workers but who work in, or frequent, the podiatric clinic shall not be exposed to more than 100 µGy/week, and should
not be exposed to more than 20 µGy/week.
3.1.2 The walls, floors, ceiling and other material constructions of podiatry rooms shall have a protective value such that no radiation in excess of the limits stated in 3.1.1 is transmitted through them to occupied positions or areas. 3.1.3 Only those personnel required to assist, or being in the course of training, should be present during the performance of x-ray examinations. 3.1.4 If installed, movable or variable protective barriers and leaded doors, etc shall be maintained in closed or protective position during x-ray examinations.
3.1.5 The occasional use of non-radiation personnel to give assistance is acceptable but shall involve the full use of protective materials and procedures. Care shall be taken to ensure that the same non-radiation personnel are not always involved.
3.1.6 There is a multiplicity of factors determining amounts of radiation reaching areas which non-radiation personnel may occupy or traverse. Where the resultant of these factors is uncertain, the use of integrating dosimeters (eg, thermoluminescent dosimeters, radiation monitoring film area monitors) is recommended to estimate the actual amounts of radiation in the occupied areas. 3.1.7 An initial inspection of a new or modified podiatric x-ray room shall
include tests or measurements for conformity of material protection with that specified in the architectural plans.
3.2 Protection of operator at the x-ray controls
3.2.1 The exposure position at the x-ray controls shall be so shielded and
located that the exposure rate is as low as is reasonably achievable, social and economic considerations being taken into account, but shall not exceed
100 µGy/week averaged over a year.
3.2.2 Where the radiation workload is sufficiently low, or where the control position is at a sufficient distance from the x-ray tube and patient that the exposure rate at the operator’s position is most likely to exceed 100 µGy/week,
a protective barrier is not required.
Note: Rule of thumb: if the podiatric radiography workload is
10 mA?min/week, the average exposure rate at the x-ray controls 1 m away from the foot or ankle being exposed will be about 20 µGy/week, averaged over general radiographic techniques. The inverse square law applies roughly for greater distances than 1 m.
3.3 Protection from exposure to the useful x-ray beam while
holding patients or image receptors in position during
3.3.1 No person shall hold a patient, x-ray film cassette, other imaging
equipment or x-ray tube head in position during exposures unless it is otherwise impossible to obtain a diagnostically useful image.
Note: Many cases of delayed radiation injury have been reported in the past resulting from frequent exposure to the useful x-ray beam while holding x-ray films in position. Injury was almost invariably to the hands. Those who suffered these injuries were lulled into a false sense of security by the absence of untoward effects in the early states (ie, a latent period). 3.3.2 Motion-restricting devices shall be applied to the patient insofar as it is
practicable; and devices for remote holding of the film cassette shall be used
3.3.3 Holding of patients of x-ray film cassettes during exposure shall be done
by persons accompanying the patient in preference to non-radiation personnel. If it is necessary to use non-radiation personnel it should not always be the same person who does the holding. No pregnant woman or young person should do any holding.
3.3.4 Any persons holding patients or film cassettes in position during exposures shall wear a leaded apron and, wherever practicable, leaded gloves. They should ensure as far as is practicable that no part of their body is in the useful beam.
4 X-RAY EQUIPMENT
4.1 Appropriate x-ray equipment
4.1.1 The x-ray machine and ancillary apparatus shall be that most
appropriate for the x-ray examination.
Note: The central considerations in this requirement are that the x-ray equipment be of maximum effectiveness in image production, and that excessive radiation doses are not delivered to patients during vain attempts to obtain acceptable images with underpowered or otherwise inadequate x-ray machines. In the main these considerations will be related to the ratings of the x-ray machine.
4.1.2 X-ray machines for podiatric radiography shall have x-ray tube current
(mA) ratings of not less than 15 mA and kilovoltage ratings of not less than 70 kV. Single pulse x-ray generators may be employed.
4.1.3 The x-ray tube should have a focal spot of nominal dimensions 1.0 x 1.0 mm or finer to help achieve high resolution images.
4.1.4 A light beam diaphragm shall be installed on the x-ray tube head for
delineation of the useful x-ray beam on the patient.
4.1.5 The x-ray equipment should be a static unit specifically designed for
podiatric radiography. Such a static unit shall include devices which permit
and if possible facilitate radiographic projections uniquely required in podiatric radiography. These shall include exposures made while in an erect and weight bearing position. A mobile or portable unit shall not be permitted unless there
is a specific requirement for such a unit, for example, use in an operating theatre.
4.2 Efficient performance of x-ray machines
4.2.1 To contribute towards an optimal level of efficiency in imaging, the x-ray equipment should perform in such a way that a close correspondence
exists between actual and nominal technique factors (kVp, mA, mAs, s) and the radiation output is consistently reproducible.
4.2.2 Any assessments of the performance of x-ray machines in respect of efficient performance should be made in terms of the parameters in paragraphs 4.2.4 - 4.2.7 inclusive. For these assessments the x-ray machine should be
connected to an electrical power supply as specified by the manufacturer for that machine. Electrical line volts shall be properly adjusted to the indicated
value where such adjustment is available to the operator. Measurements shall
be made with radiation dosemeters and other equipment calibrated and used in a manner acceptable to a qualified expert.
4.2.3 The reproducibility of x-ray output should be assessed in terms of the
coefficient of variation for specified combinations of selected x-ray machine settings. The coefficient of variation of a series of consecutive radiation exposures should not exceed 0.10 and preferably should not exceed 0.05.
(For any sample of observations the coefficient of variation is the ratio of the standard deviation of the sample to the mean value of the sample.)
Note: Experimental evidence suggests that x-ray output variations of ? 10% may be readily perceptible on radiographs.
***4.2.4 The x-ray output should be linearly related to the mA and mAs
settings within ? 10%.
* mA: X-ray tube current in milliamperes ** mAs: The product of x-ray tube current in milliamperes and exposure duration in
4.2.5 The deviations of actual peak kilovoltages from indicated or preset peak kilovoltage settings during exposure should not exceed ? 5% of the indicated
or preset value at any x-ray tube current for which the x-ray machine is properly operable.
4.3 Light beam diaphragm
4.3.1 The total misalignment of the edges of the light field with the respective edges of the x-ray field along either the length or the width of the visually defined field shall not exceed 2% of the distance from the x-ray tube focus to the centre of the visually defined field when the surface on which it appears is perpendicular to the central axis of the useful x-ray beam.
4.3.2 The centre of the light field shall be clearly indicated. The centre of the
x-ray beam and the centre of the light field shall coincide to an accuracy of
within 2% of the distance from the x-ray tube focus to the point on the illuminated surface at which it appears.
4.3.3 The brightness of the light field should be sufficiently great that the
light field is clearly visible in ambient illumination. The outer edges of the light field should be clearly shown with a high edge-field contrast ratio.
4.4 Filtration in the x-ray beam
4.4.1 Filtration shall be inserted in the useful x-ray beam to remove the
“softer” or lower energy components which otherwise contribute to patient dosage and to scattered radiation levels, without usefully affecting the diagnostic image.
4.4.2 The total filtration in the useful x-ray beam for podiatric x-ray procedures shall be not less than 2.0 mm aluminium equivalent.
4.4.3 The total filtration in the useful beam from materials it traverses in the x-ray tube and its housing (ie, the inherent filtration) should be permanently
marked on the x-ray tube housing as thickness of aluminium equivalent at a nominated kilovoltage.
4.4.4 The filtration in materials in the path traversed by the useful x-ray beam through the light beam diaphragm should be permanently marked on the outer
cover of the diaphragm as thickness of aluminium equivalent at a nominated kilovoltage.