• The Review Course in Family Medicine

"Doctor, how much radiation is in this scan?" Here's how to answer.

Updated: Aug 13, 2020

by Dr. Chinmay Dalal MD CCFP

  • Everything is Risk vs Benefit - Will this imaging aid in the diagnosis AND change management! This is key, we don’t test just to find an answer, only if it will change the management

  • Absorption of radiation is affected by body habitus

  • Modern radiology equipment is VERY focused with very little bleeding of radiation outside the targeted area

Review of the terms:

  • Millisieverts (mSv) - derived unit of ionizing radiation dose in the International System of Units (SI) and is a measure of the health effect of low levels of ionizing radiation on the human body - 1 rad = approx 10 mSv

  • Background Radiation = including radon, cosmic rays, terrestrial, and internal sources - Annually, about 3 mSv

  • The International Commission on Radiological Protection (ICRP) estimates a 4 to 5% increased relative risk of fatal cancer after an average person receives a whole-body radiation dose of 1000 mSv

ESSENTIALLY (in very general terms):

1 Chest X-Ray (PA and Lat) = 0.1 mSv of radiation = 12 days of background radiation

  • This calculation can then be used to discuss with the patient the risk vs benefit of the test and seek informed consent ie. CT Abdo/Pelvis in a patient with abdominal pain NYD ≅ 10 mSv (or 3 years of background radiation or a 0.04% increased relative risk of fatal cancer)

Photo by: Mikael Häggström / CC0, https://commons.wikimedia.org/wiki/File:Normal_posteroanterior_(PA)_chest_radiograph_(X-ray).jpg

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The only Canada-Wide CCFP exam course - created by two Family Doctors who wished this existed when we were residents, and are on a mission to help CCFP exam candidates. Disclosures: The Review Course founders have no conflicting commercial interests. As is the case with any private events hosted on a university campus or hospital, this event is not affiliated with nor endorsed by the host venues. Our materials are peer-reviewed and prepared by Canadian physicians; we do not guarantee that our preparation materials are representative of any Canadian examination and we do not provide questions from any other examination nor are they intended as medical advice. The College of Family Physicians of Canada does not affiliate with nor endorse any exam preparation course.