Answer to Question #11173 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 confused. I thought medical imaging via computerized tomography (CT) scans was safe. Over the years, due to injuries or accidents, I have had about 10 head CTs and one CT angiograph (CTA) of the head. I have had a neck CT and lung CTs when sick (but not as many lung as head CTs). Now I hear that I am at high risk for brain and other cancer. Is that true? I read a report that three-plus head CTs results in gliomas. Why would doctors order these if there is such a high risk?


There is a lot of confusing information available, much of which is frightening. Accurate information from the CT scan can ensure that you receive proper treatment following an injury or during illness. In most cases the risk of not performing the imaging scan is greater than that from the radiation. However, as a patient you should ensure that your medical providers are aware of your imaging history so that, when appropriate, they can review existing scans before ordering another. In the event of a new head trauma, it is likely that another CT scan is necessary.
Exposure to medical radiation may slightly increase the risk of future cancer, but there is no conclusive evidence. From a head CT the average effective dose is approximately 2 mSv, and the average effective dose from a neck CT is 6 mSv. The average effective dose from CTA of the brain is between 5 and 10 mSv. Your doses may vary depending on the techniques used by the imaging centers. Below 50–100 mSv risks of health effects are either too small to be observed or are nonexistent (Health Physics Society 2010). An estimate of your effective dose from all of your head and neck CT scans (including the CTA) is less than 40 mSv over the years. The American Cancer Society estimates that 42% of the people in the United States will develop some type of cancer. The possible increase in your cancer risk due to these medically necessary CT scans is a fraction of a percent.

Deirdre H. Elder, MS, CHP, CMLSO
Position Statement of the Health Physics Society. Radiation risk in perspective; 2010. Available at: Accessed 11 February 2015.

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 11 February 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.