Answer to Question #12083 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:

Q

Having had quite a few imaging studies, I have started keeping track of my lifetime exposure. I always ask any doctor ordering anything more than a plain x ray if there is an alternative and if the test is really needed. My question is about lifetime exposure. I understand that the risk of any one test, if medically necessary, is minimal. But, for example, my lifetime total exposure using dose estimates is now up to about 85 millisieverts (mSv). I am a 48-year-old female, and this seems like a lot to me, but I have no idea what is normal or average for Americans and how concerning this total is. It makes it very hard to decide to undertake or forego additional tests—my doctor now wants me to have a computed tomography (CT) angiography coronary, and I am very unsure as to whether to do it. Do you have some indication of the average lifetime exposures of Americans? What is acceptable?

A

In my field I get a lot of questions from people about their doses, and I always suggest they keep track of the diagnostic imaging tests they receive. Based on the lifetime exposure that you have calculated, your risk at this point is minimal.

We assume that certain effects of radiation, i.e., cancer, are proportional to dose. Radiation does not accumulate in the body, but we assume the risk is cumulative so as to err on the side of caution. Most of our risk data is based on doses greater than 100 mSv that are received over a very short time period. We take the known risks of these higher levels of exposure over a short amount of time and extrapolate down to assumed risk at lower levels of exposure. If your exposure of 85 mSv is taken over your entire lifetime, your total exposure is actually fairly minimal.

You asked about average lifetime exposures; the Health Physics Society has a very good fact sheet on annual background radiation exposures. Everyone receives about 3.1 mSv annually from natural background radiation. Adding medical procedures and other man-made radiation exposures, the average annual effective dose is 6.2 mSv annually per person in the United States.

I would suggest you look at the benefit of your exams versus the risk. A CT angiography can expose you to 5–32 mSv. Even at 32 mSv, the risk is minimal, but the benefit from what the physician can see may be very great. What I tell people to question is if the doctor is asking to repeat the same procedures; sometimes they may be able to see what they need from a previous exam if it was done fairly recently and there have been no health changes. Another very good website with information for patients on radiation exposure is www.imagewisely.org.

In the medical community, the appropriateness of an exam should always be evaluated to ensure that the benefit of the procedure exceeds the potential risk. As I mentioned, based on the lifetime exposure that you have calculated, your risk at this point is minimal. I always suggest to anyone they speak with their physician about the benefits of any radiation procedures they are suggesting.

Sarah Hughes, MS, DABR

Editor's note: I would caution you about forgoing additional tests; refusing medical imaging procedures may result in real and substantial risk to the patient who will not receive the clinical benefits of the procedures.

Answer posted on 1 January 2018. 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.