Answer to Question #11982 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 have had health anxiety for quite some time. With my frequent trips to the emergency room and frequent testing, I've accumulated around 170 millisieverts (mSv) of radiation exposure on top of my natural exposure. Does this amount of exposure put me at a more appreciable risk than the 100 mSv value I've seen mentioned on the Health Physics Society website several times? Most of my exposure has come over the past 10 years in the form of computed tomography (CT) scans. I'm just not clear as to the scalability of risk. I'm also not clear on the cumulative effect. How can risk be cumulative if your body rapidly repairs cells?


I am sorry that you have experienced health issues and I don't want you to endure additional anxiety due to the medical imaging you have received. The additional cancer risk, if any, is very low.

Scientists are still studying the effects of low doses of radiation, such as that from medical imaging. There is a lot of uncertainty regarding the risks associated with small radiation doses, especially when accumulated over a long period of time. But even with radiation doses higher than those you received, the additional risk of cancer is very small compared to the natural incidence.

You are right that the cells in our bodies repair a lot of the damage that can be caused by radiation or by other insults, such as chemicals. Unfortunately, the damage isn't always repaired correctly. Researchers are working to better understand how the risk scales at low doses and the cumulative effect of doses received over periods of years. What we do know is the risk at these doses is low.

We recommend that you talk to your health care providers before future CT scans to decide whether the CT scan is justified and whether it will provide information needed to guide your medical care. You might ask whether another type of imaging would provide the information needed. Standard x rays use much less radiation, and ultrasound and magnetic resonance imaging (MRI) techniques don't use any ionizing radiation. In some cases, these would be appropriate. In most cases, the risk from medical imaging that is justified is much lower than the risk of the medical complications that could occur without the scan.

Please rest assured that the risk from the CT scans you have had is very small.

Deirdre H. Elder, MS, DABHP, CMLSO

Editor's Note: The Health Physics Society's position statement Radiation Risk in Perspective states, "The references to 100 mSv in this position statement should not be construed as implying that health effects are well established for doses exceeding 100 mSv. Considerable uncertainties remain for stochastic effects of radiation exposure between 100 mSv and 1,000 mSv, depending upon the population exposed, the rate of exposure, the organs and tissues affected, and other variables."

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 18 July 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.