Answer to Question #11855 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:


On New Year's Eve, I had a computed tomography (CT) exam of my head without contrast to check for ringing in my ear and possible infection from an abscessed tooth. A few days later, I went to a root canal expert to have a consultation concerning root canal procedures. During that time, they did three panoramic x rays (the machine stuck on my shoulder at one point) and four bitewing x rays of the problem tooth. I did not know that the CT exam involved x-ray levels much higher than a normal chest x ray, so I am concerned about the cumulative effect of so much radiation exposure to my head in such a short period of time. Please let me know if my concerns are justified as I am very anxious and worried.


You can stop worrying; the risks of health effects from radiation doses received during diagnostic imaging procedures, including CT scans, are either too small to be observed or are nonexistent.

Typical doses from a head CT and the few dental procedures you underwent would be in the range of 2–3 millisieverts (mSv). At radiation doses above 100 mSv there is clear and convincing evidence of health effects. However, health risks for radiation doses below 100 mSv are statistically equal to zero; in other words, they are too small to be seen or are nonexistent. Any prediction of risk from radiation exposures below 100 mSv is hypothetical and cannot be supported by scientific evidence. The Health Physics Society's position statement "Radiation Risk in Perspective" explains in more detail health risks from low-dose radiation. Some risk information is also available from

The American Association of Physicists in Medicine, a scientific organization dedicated to the safe use of radiation in medicine, has a risk statement that reads, in part: "Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent."

Kent Lambert, CHP

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 7 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.