Answer to Question #11836 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 recently had a computed tomography (CT) colonoscopy. I was told my dose was around 7.8 millisieverts (mSv). I've been extremely anxious about my risk of getting cancer from the scan since I started to Google it.

There are so many conflicting stories out there—some say there's no proof that doses under 50 mSv causes any harm. Then I read answers to questions on here saying your chance of getting cancer may be 1%, etc. I'm a 37-year-old female and have two very young children. Please tell me if I should be worried or not and if there is a chance I've increased my risk of getting cancer.


The risks of health effects from radiation doses received during diagnostic imaging procedures are either too small to be observed or are nonexistent. We are all at risk of developing cancer; approximately 37.5% of all women in the United States will develop cancer in their lifetimes. If every woman in America received a CT colonoscopy, we would still not be able to see a difference in the cancer rate.

The benefits from properly performed, clinically indicated, diagnostic imaging procedures, including CT scans and CT colonoscopies, far outweigh any hypothetical cancer risk. Diagnostic medical imaging procedures provide a medical benefit to you, even if they do not appear to reveal anything, and are of less risk than their alternatives, such as exploratory surgery.

Even if the result of the imaging exam was negative, the physicians were provided information they could use to determine the next course of action. Refusing medical imaging procedures may result in real and substantial risk because you won't receive the clinical benefits of the procedures.

The dose you were told, 7.8 mSv, is typical for CT colonoscopy. Because the Health Physics Society recommends against quantitative estimates of health risks for radiation doses below 100 mSv, we will not calculate hypothetical risks for diagnostic imaging procedures. The Society's position statement "Radiation Risk in Perspective" explains in more detail why it is inappropriate to estimate health risks at these doses. Some risk information is also available from

Kent Lambert, CHP

Answer posted on 5 February 2017. 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.