Radiation exposure to patients is kept “as low as reasonably achievable (ALARA)”
- Radiation used in medicine accounts for more than 90% of the total man-made radiation dose to the general population1.
- In general, the benefits of administering ionizing radiation for imaging and therapeutic purposes outweigh the risks as long as radiation protection/safety guidelines are adhered to.
- The aim of radiation protection, according to the International Commission on Radiation Protection is to “provide an appropriate standard of protection for man without unduly limiting the beneficial actions giving rise to radiation exposure”2
- The ALARA principle was created to reduce the probability of detrimental effects of radiation and reduce overall risk to patients3.
- Current models of radiation protection are based on the conservative assumption that any level of radiation, no matter how small, has the potential to increase the risk of cancer.
- The principle holds for any procedure or intervention in which risk increases with dose, whether it be ionizing radiation or otherwise
- Because risk increases with dose, there should always be an effort to perform procedures with a dose that is “as low as reasonably achievable” (ALARA).
- It is insufficient for an MRT to simply respect the appropriate dose limits; efforts must always be made to keep dose to a minimum while maintaining quality.
- Managing patient radiation dose involves a complex interaction of factors that differ by discipline and procedure4,5.
- Some important common factors include4,5:
- Source of radiation
- Length of exposure
- Distance from the source of radiation
- Protective measures (quality control, shielding, etc.)
- The ALARA principle is used when judging the appropriateness of an imaging procedure, or planning for radiation therapy treatments6:
- Use of radiation is optimized to obtain maximum benefit with the minimum of exposure
- Relative risks and benefits are weighed against feasible alternatives – modalities that do not use ionizing radiation are considered to limit patient exposure to radiation
- MRTs are responsible for quality control and proper preparation which will help minimize repeat procedures, for example:
- Images that are diagnostic, with clearly identifiable pathology, should not be repeated because of suboptimal image quality
- If there is uncertainty about the need for a repeat procedure, a radiologist or a more experienced MRT is consulted
- Proper quality control of the equipment and, in the case of nuclear medicine, of the radiopharmaceutical is assured prior to undertaking the procedure
- Appropriate instructions are given to the patient prior to and following procedure/treatment
- MRTs are responsible for determining the need for additional radiation safety actions before a radiation exposure, for example7:
- Recognition of patients and/or body parts that require special protection because of higher sensitivity to radiation
- Potential for devices (e.g., implanted cardiac devices) which may be in the proximity of the radiation field
- Use of appropriate scanning borders (taking into account the patients’ histological diagnosis) when performing CT simulation
- Proper documentation helps to ensure that diagnostic examinations are preserved for future use, circumventing the need for a repeat investigation.
- Technical parameters to further reduce doses include1:
- Filtration of soft radiation
- Collimation of beams
- Selection of automatic exposure control (AEC) sensors
- Appropriate focal spot-to-skin distance
- Adaptation of technique for children and different body types
- MRTs can consult with their radiation safety/protection officer for additional information.
Health Canada. Safety Code 35: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities. Available from: http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/safety-code_35-securite/index-eng.php. [Accessed 30 Jan 2018]
Hall EJ, Giaccia AJ, eds. Radiobiology for the Radiologist. 6th ed. Philadelphia, PA: Lipincott, Williams and Wilkins; 2006.
Canadian Nuclear Safety Commission. Keeping Radiation Exposures and Doses “As Low as Reasonably Achievable (ALARA)”, G129 revision 1. Available from: http://www.nuclearsafety.gc.ca/pubs_catalogue/uploads/G129rev1_e.pdf. [Accessed 30 Nov 2018]
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.
Reynolds A. Patient-centered care. Radiol Technol 2009;81(2):133–147.
Canadian Association of Radiologists. 2012 CAR Diagnostic Imaging Referral Guidelines. Available from: https://car.ca/patient-care/referral-guidelines/. [Accessed 12 Dec 2018]
Amis ES, et al. American College of Radiology White Paper on Radiation Dose in Medicine. J Am Coll Radiol 2007;4:272-284.