COMP Report: A survey of radiation safety regulations for medical imaging x‐ray equipment in Canada

Abstract X‐ray regulations and room design methodology vary widely across Canada. The Canadian Organization of Medical Physicists (COMP) conducted a survey in 2016/2017 to provide a useful snapshot of existing variations in rules and methodologies for human patient medical imaging facilities. Some jurisdictions no longer have radiation safety regulatory requirements and COMP is concerned that lack of regulatory oversight might erode safe practices. Harmonized standards will facilitate oversight that will ensure continued attention is given to public safety and to control workplace exposure. COMP encourages all Canadian jurisdictions to adopt the dose limits and constraints outlined in Health Canada Safety Code 35 with the codicil that the design standards be updated to those outlined in NCRP 147 and BIR 2012.

oversight might erode safe practices. Harmonized standards will facilitate oversight that will ensure continued attention is given to public safety and to control workplace exposure. COMP encourages all Canadian jurisdictions to adopt the dose limits and constraints outlined in Health Canada Safety Code 35 with the codicil that the design standards be updated to those outlined in NCRP 147 and BIR 2012.

| BACKGROUND
Canada has adopted the guidelines of the International Commission on Radiological Protection (ICRP) on occupational dose limits for radiation. Starting with the publication of ICRP 26 1 in 1977, estimates were given of the radiation sensitivities of various organs and tissues (w t ), and the whole-body dose was considered as the sum of doses to all organs and tissues each weighted for their radiation sensitivities.
Publication ICRP 60 (1991) 2 improved upon ICRP 26 with better data on radiation sensitivities. Equivalent dose (H R ) was defined as the absorbed dose multiplied by a radiation weighting factor (w R ) related to relative biological effect of a given type of primary radiation. For xray photons of concern here, w R = 1. Effective Dose (E) was defined as the sum of the equivalent dose to each organ or tissue weighted by the relevant radiation sensitivity. ICRP 103 (2007), 3 using new data, further refined the tissue sensitivities. The tissue weighting factors from the different ICRP reports are compared in Table 1 and it is noteworthy that these weighting factors change over time as the understanding of the effects of radiation on human biology improves.
At the time of publication for ICRP 103, the occupational limit for eyes was under review, and ICRP 118 was subsequently published recommending a lower limit for the eyes. 4 The recommended stochastic dose limits from ICRP 60, 103, and 118 are shown in Table 2

2.B | Optimization
The dose limits in Table 2  • No information on modalities such as computed tomography (CT), mammography, and digital imaging.
• Attenuation data were not applicable to three phase or constant potential generators.
• Typical mAs workloads were no longer valid due to the use of newer high speed rare-earth film/screens.
• The use factors and occupancy factors appeared to be unrealistically high.
• Shielding was specified using half-value-layers (HVLs) of Pb or concrete required to attenuate scattered and primary radiation to designed levels, and the requirement to "add-one-HVL" was considered overly-conservative.
• The requirement to cover screws or nails with Pb tabs was questioned.

4.B | Dose limits
As shown in Table 4, many jurisdictions use the annual dose limits from SC 20A; that is, 50 mSv for x-ray workers, 1 mSv for the public, and 4 mSv for the remainder of a pregnancy following declaration. A few provinces have adopted the more recent 20 mSv for radiation workers from SC 35, and some jurisdictions have no limits due to the lack of regulations. For jurisdictions without regulations, institutions or authorities usually set their own limits as best practice, but there is a risk they might not.

4.C | Shielding of x-ray facilities
No two provinces or territories have the same standards for the shielding of x-ray facilities, as shown in more specifically define the practice of engineering as "the principles of mathematics, chemistry, physics or any related applied subject" and Prince Edward Island has similar wording, Note 6 whereas Quebec considers the field of practice to include works using "processes of applied chemistry or physics." Note 7 In practice, most jurisdictions do not formally require an engineer's oversight for a shielding design, with the exception of Quebec and Ontario. As part of any engineering design work, field reviews are required, which include visual inspections and scatter surveys in Table 5. Consequently, with regards to Table 6, an engineer is not obligated to use only specific design documents permitted by regulations or accreditation agencies, but are expected to use any and all methodologies that would be considered good practice and obvious to peers performing similar design work.
As shown in Table 6, for all provinces with regulations, except Ontario, NCRP147 is identified as the main source of information for the design of x-ray shielding. In Ontario, assuming a radiographic detector has a certain Pb equivalency as suggested by NCRP 147 has to be approved by the x-ray inspection service. Many provinces    There is a wide range of annual dose constraints used for the design of shielding, as shown in Table 7. For x-ray workers, where there are regulations, the range is 1 to 50 mSv, and the range for the General Public is 1 to 5 mSv. It is also interesting to note that the constraints and dose limits (Table 4) are often different. An appropriate and conservative approach, and one recommended by the authors of this paper who perform shielding design, is to set a shielding design goal of 1 mSv for all cases, allowing future use of adjacent spaces to change without the need to change shielding, for example, if an office fully occupied by a radiation worker becomes office space for a nonradiation worker (general public).

1990-2016
The average and median annual occupational dose for radiographic technologists in Canada are shown in Fig. 1. The average value for 2016 is approximately 0.10 mSv/yr and the median value is zero.
Technologists working in FGI procedures, who typically experience higher occupational exposures, were not separated from technologists exclusively working in general radiography. The Canadian average is slightly higher than the UK radiographer average value of 0.06 mSv/yr. 6 It appears that the BIR recommendations to use a dose constraint of 30% of the dose limit (or 0.3 mSv) would also be applicable to Canadian practice, since this constraint level is already achieved, especially considering the measured values reported here include staff who are exposed to workplace radiation without protection from structural shielding, including technologists who work in FGI procedures.
A breakdown of radiographer occupation exposure by different dose ranges is shown in Fig. 2  distinction between diagnostic x-ray personnel and nuclear medicine personnel in terms of permissible exposure, but the latter of course are monitored under the CSNC regulations. In practice, it is the experience of these authors that x-ray radiation workers rarely exceed an occupational exposure of 1 mSv/yr, whereas a nuclear medicine radiation worker has a much higher probability of doing so.

| CONCLUSIONS
In the interests of public safety and to control workplace exposure, it would be useful for different jurisdictions in Canada to adopt a harmonized approach, by implementing uniform dose limits and con-