Answer to Question #11307 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:


I am 50 years old and had to have a bone scan and abdomen/chest and pelvic computerized tomography (CT) for back problems. Thank goodness all was clear; however, my dose was 18 millisieverts (mSv).

I do believe I was overexamined. There is nothing I can do now, but I am worried about the 18 mSv exposure and getting cancer. Could you help me understand this?


Thank you for your question to the Health Physics Society Ask The Experts. Any increase in your cancer risk is minimal if it exists at all. The Health Physics Society's position statement on radiation risk states that "below levels of about 100 mSv above background from all sources combined, the observed radiation effects in people are not statistically different from zero." In other words, the risk, if it exists, is too small to be seen.

This is similar to the American Association of Physicists in Medicine's position on radiation risks from medical imaging procedures:
"Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent. Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low doses are highly speculative and should be discouraged."

An effective dose of 18 mSv is well below that for which an increase in risk can be seen.  

These procedures provided a medical benefit to you even if they did not appear to reveal anything. That nothing was seen gave your physicians information that they could use to determine the best next course of action. The risk from diagnostic imaging procedures, including CT scans, when properly performed and clinically indicated is very small compared to the diagnostic benefit they provide.
Kent Lambert, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 16 October 2015. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.