Answer to Question #12830 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 know you do not calculate risk, but I am struggling to understand all of the statistics I read online. I was in an accident when I was 13. I had a full-body computerized tomography (CT) scan and a follow-up head CT a year later. This was at a pediatric facility. Fast forward to now. I recently had a CT pulmonary angiogram (PA) to rule out an embolism two days after having my baby. I keep reading statistics about how 1 in 80 CT PA leads to cancer in a young woman. Or I see 1 in 143. Just for this one scan. When I add in my full-body scan as a child, I can't help but feel I am doomed to develop cancer. Is there anything I can learn to help reassure me? 


Your CT scans have not doomed you to develop cancer. The risks that you see online are hypothetical risks determined by assuming that there is some increase in risk. But, at radiation doses seen from diagnostic imaging, including CT scans, the risk cannot be scientifically proven. Radiation risk has only been observed at much higher doses. In other words, scientific evidence does not support the risks you quoted.  

Your CT scans would be well below 100 mSv. If the effective dose is less than 100 mSv the risk is too small to be seen, if a risk exists at all. This is why we do not calculate risks. At radiation doses associated with CT scans and other diagnostic imaging, we would be calculating a theoretical risk that has not been observed and cannot be proven scientifically. For more information on the risk you may want to check out the HPS position statement, Radiation Risk in Perspective and the American Association of Physicists in Medicine (AAPM) position statement on radiation risk from medical imaging procedures.  

The bottom line is that your cancer risk is virtually the same now as it would have been if you did not have the CT scans. For women living in the United States, the chance of developing cancer in their lifetime is around 37.5%, or 1 in 2.67. 

Kent Lambert, CHP, FHPS

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 April 2019. 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.