Answer to Question #13829 Submitted to "Ask the Experts"
Category: Medical and Dental Patient Issues
The following question was answered by an expert in the appropriate field:
I'm reading Chris Beat Cancer by Chris Wark. He cites a source from 2012, written by Mark S. Pearce and team in The Lancet, saying that cumulative exposure of 50–60 mGy of radiation from computed tomography (CT) scans before age 15 can triple risk of developing brain cancer and leukemia in the future. I suffered a traumatic brain injury when I was 13. I received three head CT scans that summer, another a year later, and another during my following yearly checkup. I am now an adult. Am I three times more likely to develop brain cancer?
I want to begin by reassuring you that the CT scans you received have not significantly increased your risk of developing cancer. In the cited study, the total number of brain cancers was less than 0.08% of the individuals who received head CT scans as children. The paper states
Use of CT scans in children to deliver cumulative doses of about 50 mGy might almost triple the risk of leukaemia and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: in the 10 years after the first scan for patients younger than 10 years, one excess case of leukaemia and one excess case of brain tumour per 10,000 head CT scans is estimated to occur. Nevertheless, although clinical benefits should outweigh the small absolute risks, radiation doses from CT scans ought to be kept as low as possible and alternative procedures, which do not involve ionising radiation, should be considered if appropriate.
There are two things to keep in mind when reviewing studies such as this. The first is that there is a lot of uncertainty in the risk values. The second thing to remember is that the authors imply causation without taking into account that there can be a correlation between having a condition that results in a child having several head CT scans and a higher risk of developing cancer later. The authors do not address either correlation or causation in the paper. It is also important to understand that there is a definite benefit to the CT scan. The information from the CT scan allows the physician to make an accurate diagnosis and provide appropriate treatment. For that reason, even the authors of the paper do not indicate that CT scans are not appropriate for children.
There are other studies that show no difference in cancer risk with doses below 100 mSV above background. The average effective dose from natural background is approximately 50 mSv in the first 17 years and 250 mSv during an average 80-year lifetime. The Health Physics Society position on radiation risk is that health risks should not be estimated for exposures that are near background levels.
Your risk of developing brain cancer during your lifetime is essentially the same as for those who have not had head CT scans. Please do not continue to worry.
Deirdre H. Elder, MS, CHP, CMLSO