05.01.01. Minimizing MRT exposure
Radiation exposure to MRTs is kept “as low as reasonably achievable” (ALARA)
Radiation limits
- After extensive study of the deterministic and stochastic effects of radiation on the human body, the International Commission on Radiation Protection (ICRP) formed recommendations on dose limits for the people who work with radiation1.
- In Canada, the Canadian Nuclear Safety Commission (CNSC) recommends dose limits for Nuclear Energy Workers (NEWs) and the provinces recommend doses for Radiation Workers2.
- The effective dose limit for NEWs, as prescribed by the CNSC, is 100 mSv in 5 years (with a maximum of 50 mSv in any given year or an average of 20 mSv/yr for 5 years) for whole-body exposure3-5.
- The cumulative lifetime dose should remain below 10 mSv multiplied by age3
- The equivalent dose limit for Radiation Workers, as recommended by the ICRP (and Health Canada through Safety Code 35 ), is 20 mSv in a year for whole body exposure6.
Minimizing dose
- The same factors that determine patient exposure to radiation apply for MRTs3,7,8:
- Time of exposure (e.g., number of scans, time of exposure to the radioisotopes)
- Distance from the source of radiation
- Shielding with absorbent materials
- The ALARA principle is used to guide the professional’s interaction with radiation3,4:
- MRTs are aware of all possible sources of radiation in their environment –equipment (whether on or off), radiopharmaceuticals and patients
- The least possible amount of time is spent in the proximity of a source of radiation
- Immobilization devices should be used where possible, otherwise a family member or other healthcare professional may be asked to hold the patient
- Shielding is used wherever appropriate, including mobile and stationary barriers, shielding garments and lead eye protection (or goggles)
- MRTs likely to exceed a radiation dose of 1/20th of the recommended ICRP exposure limit are declared radiation workers and wear personal dosimeters to accurately monitor their exposure4.
- Good planning and quality control can also help minimize exposure from certain sources of radiation.
- CNSC regulations are followed for all components of construction or renovation of areas where radiation equipment will be placed9
References
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International Commission on Radiological Protection. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).
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Canadian Nuclear Safety Commission. Radiation Doses. Available from: http://www.nuclearsafety.gc.ca/eng/resources/radiation/introduction-to-radiation/radiation-doses.cfm. [Accessed 1 May 2018]
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Adler AM, Carlton RR. Introduction to radiologic sciences and patient care. 3rd ed. St. Louis, MO: Saunders; 2003.
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Government of Canada, Justice Laws Website. Radiation Protection Regulations (SOR-2000-203/page 4). Available from: http://laws-lois.justice.gc.ca/eng/regulations/SOR-2000-203/page-4.html. [Accessed 30 Apr 2018]
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Health Canada. Safety Code 35: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities. Appendix 1: Dose Limits for Occupational Ionizing Radiation Exposures. Available from: https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radiation/safety-code-35-safety-procedures-installation-use-control-equipment-large-medical-radiological-facilities-safety-code.html#app1. [Accessed 26 April 2018]
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Strauss KJ, Kaste SC. The ALARA (As Low As Reasonably Achievable) Concept in Pediatric Interventional and Fluoroscopic Imaging: Striving to Keep Radiation Doses as Low as Possible during Fluoroscopy of Pediatric Patients—A White Paper Executive Summary. Radiology 2006;240:621-622.
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Reynolds A. Patient-centered care. Radiol Technol 2009;81(2):133–147.
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Canadian Nuclear Safety Commission. Design Guide for Nuclear Substance Laboratories and Nuclear Medicine Rooms, GD-52. May 2010. Available from: http://nuclearsafety.gc.ca/pubs_catalogue/uploads/GD-52_Design_Guide_for_Nuclear_Substance_Laboratories_and_Nuclear_Medicine_Rooms.pdf. [Accessed 1 May 2018]