Answer to Question #11310 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues ā€” Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:


My son is eight months old. He had to have a computed tomography (CT) scan of his head after a fall followed by vomiting. His dose was 366 milligray-centimeters (mGy-cm). I'm now very concerned about his dose because he is so young. Obviously, I wish I could undo the whole event of him falling. While I'm thankful his CT scan was negative for bleeding or fracture, I'm sick to my stomach about his dose. Iā€™m worried that he could develop cancer or leukemia in the future. How bad is it for a baby to receive a CT scan of the head?


The simple answer is that the long-term risk of cancer or leukemia from your son's head CT scan is extremely low and more likely, nonexistent. It was very helpful that you provided the dose-length-product (DLP) value (in mGy-cm) for the scan. Based on a report published by the American Association of Physicists in Medicine, the estimated effective dose from this CT scan can be calculated to be about 2.8 millisieverts (mSv).

To put that number in perspective, the National Council on Radiation Protection and Measurements estimates that an average member of the U.S. population receives an effective dose of about 3.1 mSv every year from natural background sources such as radon, radioactive materials in soil and rock, and radiation from outer space. Individuals who live in Denver, Colorado, receive about 50% more than that average because Denver is at a higher altitude and has more naturally occurring radioactivity in the soil and rock. Even though individuals who live in Denver receive above-average effective doses from these natural sources (they get about as much additional effective dose every two years as your son received from the head CT scan), the incidence of cancer and leukemia there is essentially no different than the rest of the United States.

The Health Physics Society (HPS) is an organization that continually looks at various aspects of radiation protection, including radiation risks. The following paragraph appears in the HPS's "Radiation Risk in Perspective" Position Statement: "There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 50ā€“100 mSv (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are nonexistent."

The HPS also supports the idea that the benefit from any radiation exposure should outweigh the risk. In your case, your son was presenting with symptoms that led the physician to believe there was a real risk of head injury, and the CT scan allowed the physician to rule out potentially serious medical problems that may have required treatment. In other words, the benefit from the information provided by the CT scan far outweighed the vanishingly small or possibly nonexistent risk from the CT scan.

Mack L. Richard, MS, CHP


  • American Association of Physicists in Medicine. The measurement, reporting, and management of radiation dose in CT. College Park, MD: American Association of Physicists in Medicine; AAPM Report No. 96; 2008.
  • Health Physics Society. Radiation risk in perspective. Health Physics Society Position Statement. Available at Accessed 22 January 2016.
  • National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. Bethesda, MD: National Council on Radiation Protection and Measurements; NCRP Report No. 160; 2009.
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 25 January 2016. 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.