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Minimizing patient exposure


Radiation exposure to patients is kept "as low as reasonably achievable (ALARA)"


+ Risks of radiation

  • Radiation used in medicine accounts for more than 90% of the total man-made radiation dose to the general population.1
  • 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 patients.3
  • 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. 

+ Minimizing dose

  • Managing patient radiation dose involves a complex interaction of factors that differ by discipline and procedure.4,5
  • Some important common factors include:4,5
    • 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 treatments:6
    • 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 example:7
    • 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 include:1
    • Filtration of soft radiation
    • Collimation of beams
    • Selection of automatic exposure control (AEC) sensors
    • Shielding
    • 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.

+ References

  1. Health Canada. Safety Code 35: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities. Available at: Accessed April 3, 2012.
  2. Hall EJ, Giaccia AJ, eds. Radiobiology for the Radiologist, 6th ed. Philadelphia, PA: Lipincott, Williams and Wilkins; 2006.
  3. Canadian Nuclear Safety Commission. Keeping Radiation Exposures and Doses "As Low as Reasonably Achievable (ALARA)". Available at: Accessed April 4, 2012.
  4. 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.
  5. Reynolds A. Patient-centered care. Radiol Technol 2009;81(2):133-147.
  6. Canadian Association of Radiologists. Diagnostic Imaging Referral Guidelines: A guide for physicians. 1st Ed., 2005. Available at: Accessed April 4, 2012.
  7. Amis ES, et al. American College of Radiology White Paper on Radiation Dose in Medicine. J Am Coll Radiol 2007;4:272-284.




May 25, 2012


Canadian Association of Medical Radiation Technologists
85 Albert St, Suite 1000, Ottawa, ON, K1P 6A4
phone: 613 234-0012 / 800 463-9729
fax: 613 234-1097