Guidance on optimization of radiation protection of workers can be found in the 1990 Recommendations of the International Commission on Radiological Protection (ICRP 60) and Radiological Protection and Safety in Medicine (ICRP 73) from the International Commission on Radiological Protection.
The three fundamental principles of radiation protection from ICRP 60 are:
- the practice involving exposure to radiation is justified by the benefit obtained from the practice;
- all exposures should be kept As Low As Reasonably Achievable (ALARA), economic and social factors being taken into account; and
- dose limits should be applied to provide an adequate standard of protection even for the most highly exposed individuals.
Dose Limits for Workers
Occupational exposures to medical x-rays in British Columbia are regulated provincially by WorkSafeBC (WSBC) and federally by Health Canada. Based on WSBCs Occupational Health and Safety Regulations, the dose limits for workers are:
- an annual effective dose of 20 mSv (whole-body dose)
- an annual equivalent dose of:
- 150 mSv to the lens of the eye
- 500 mSv to the skin, averaged over any 1 cm2 regardless of the area exposed, and
- 500 mSv to the hands and feet
In addition to these dose limits, WSBC has also defined an Action Level of 1.0 mSv/y. If the exposure of the worker exceeds or may exceed an annual dose of 1.0 mSv, employers must:
- provide and ensure the proper use by workers of an acceptable dosimeter or radiation badge;
- perform radiation surveys to measure radiation levels in work areas; and
- provide written instructions on safe and proper procedures and practices related to the use of the radiation-emitting device.
Other requirements are listed in WSBCs Occupational Health and Safety Regulations Part 7.
Dose Limits for the Pregnant Worker
Special limits are imposed for pregnant workers as an additional control to enhance the protection of the unborn child. ICRP guidance for pregnant workers can be found in Pregnancy and Medical Radiation (ICRP 84) or as a PowerPoint presentation. The worker should inform his or her supervisor once she knows of her pregnancy. Once the worker has declared her pregnancy, the special limits for the pregnant worker for the remainder of her pregnancy in WSBCs Occupational Health and Safety Regulations is the lesser of:
- effective dose of 4 mSv
- dose limit specified for pregnant workers under the Nuclear Safety and Control Act or any successor legislation, and the regulations under that Act.
RIN 5 - Foetal Dose from Maternal Diagnostic X-ray Examinations document provides guidance for practitioners in the radiology field when addressing embryo dose.
Monitoring Exposure (Radiation Badges)
For more information, refer to RIN 7 - Update On Personal Dosimetry Services, which provides an advisory on personal radiation dosimetry services in Canada.
RIN 13 - Procedures for Reporting and Investigating High Occupational Radiation Exposure Notifications. An employer may receive a notification from the dosimetry service provider or from the National Dose Registry (NDR) of Canada (NDR), indicating that an employee has exceeded an applicable dose limit. These notifications can result from a high dose on an individual badge or from the accumulation of the doses received from badges worn during the year. The employer is responsible for taking action on receipt of a notification.
RIN 21 - Guideline for Wearing Radiation Monitoring Devices [Personal Dosimeters] or TLDs: provides guidance to owners/operators in facilities where ionizing radiation is used on the need for wearing personal radiation monitoring devices (i.e. dosimetry badges).
RIN 22 - Guidelines for Workers Assisting During Medical X-ray Procedures provides guidance for workers who assist in medical procedures that involve the use of x-ray equipment.
Dosimetry Services
The following three dosimetry service providers are currently approved in Canada:
They offer whole-body and extremity thermo-luminescent dosimetry services (TLD). Monitoring periods are usually quarterly but more frequent monitoring is also available for pregnant workers. In cases where the dose limits are exceeded, the client is notified.
WorkSafeBC (WSBC) requires that: “Unless exempted by the Board, if a worker exceeds or may exceed the action level (1 mSv/y), the employer must ensure that the worker is provided with and properly uses an acceptable personal dosimeter”. It further requires that the employer must ensure that every worker who exceeds, or may exceed, the action level is fully informed of any potential reproductive hazards associated with radiation exposure. The Canadian Nuclear Safety Commission, on the other hand, requires that if there is reasonable probability that a worker who, by the nature of his/her work involving nuclear substances, may exceed the dose limit for the public of 1 mSv/y, should be informed of the risks of radiation exposure and be considered as a Nuclear Energy Worker (NEW).
Protective Items (Lead Aprons)
The basic steps to reduce exposure to radiation are:
- minimize time exposed to the radiation-emitting device or source to as short as possible;
- increase distance from the radiation-emitting device or source to as far as practicable;
- wear protective items that provide effective shielding such as lead aprons, thyroid collars, and gauntlets.
More information about lead aprons is provided in RIN 10 - Proper Selection, Care, Quality Control and Disposal of Lead Aprons. Protective items should be checked regularly for defects, cracks or holes because the level of protection provided by these items can be compromised by such defects. Guidance on when to reject defective aprons and other lead apparel is provided in a BCCDC 2003 Report entitled Rejection Criteria for Defects in Lead Apparel Used for Radiation Protection of X-ray Workers. Facility owners can choose to establish a more restrictive criteria as may be appropriate to their circumstances.
