Answer to Question #11310 Submitted to "Ask the Experts"
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. I’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. According to the HPS's "Radiation Risk in Perspective" Position Statement, "below levels of about 100 mSv above background from all sources combined, the observed radiation effects in people are not statistically different from zero." In other words, the risk, if it exists, is too small to be seen.
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 http://hps.org/documents/radiationrisk.pdf.
- 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.