Risks from childhood CT scans: real, but very small

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A study just published in The Lancet has found that radiation exposure from repeated CT scans in childhood might significantly increase the admittedly low risk of leukemia and brain cancer. As the study authors note, because such cancers are rare to begin with, the risks for children undergoing CT scans remain exceedingly small.

With the understanding that children are more sensitive to ionizing radiation than adults are, researchers funded by the UK Department of Health and the US National Cancer Institute set out to determine whether there was a correlation between multiple CT scans in childhood and an increased incidence of two specific cancers. To do this, the researchers looked at the radiology records of nearly 180,000 UK patients who had undergone a CT scan between 1985 and 2002, estimating the dose absorbed by the brain and bone marrow in each case. They then linked these data to cancer incidence and mortality reports in the UK National Health Service Registry between 1985 and 2008, enabling them to calculate the rate of leukemia and brain tumors amongst CT scan recipients and to determine the excess occurrences attributable, it was thought, to the radiation absorbed.

While the findings confirm the researchers' hypothesis, it's important to keep the actual numbers in mind. Out of about 180,000 patients, a total of 74 were diagnosed with leukemia, and 135 with brain cancer. This means that, for every 10,000 people aged 20 and below there would be one expected excess case of leukemia. One excess brain tumor would occur for every 30,000 of the same demographic. Thus, the study authors emphasize, the absolute risk of developing these diseases remains very low and does not outweigh the clinical benefits in cases where a CT scan is contemplated for valid medical decision-making. However, they advise that radiation doses from these scans should be kept as low as possible and alternative procedures be used when available.

ACSH's Dr. Gilbert Ross agrees with the study authors' conclusions. "While there's not a false word in the study," he notes, "the findings are being blown out of proportion by the news media. To speak of tripling the risk of cancer in a child will frighten a lot of parents; they need to understand that the absolute risk is still very, very low. There are many instances when a CT scan is necessary for a diagnosis. Furthermore," he says, "there have already been major improvements in CT scan technology with lower radiation dosage since the time period from which these data were accumulated, over ten years ago. Physicians should be aware of the possible risk and avoid using a CT to diagnose something like appendicitis, where alternative diagnostic tools (e.g. sonograms) are available. But it shouldn't prevent them from using the necessary CT-scan when it comes to diagnosing things like trauma to the head, neck, or spine, as well as various neurological disorders."