CT scans increase risk of pediatric cancers

In children younger than 15 years, 2 to 3 computed tomography (CT) scans of the head might triple the risk of brain tumors; 5 to 10 of them might triple the risk of leukemia.

These findings come from a retrospective cohort study jointly funded by the UK Department of Health and the US National Cancer Institute, part of the National Institutes of Health.

The study looked at nearly 180,000 patients from a wide range of hospitals in the United Kingdom who first received a CT scan between 1985 and 2002 when they were younger than 22 years. These patients were followed for leukemia beginning at 2 years after the first CT scan and for brain tumor at 5 years. The researchers counted 74 leukemia diagnoses in 178,604 patients and 135 brain cancer diagnoses in 176,587 patients. They calculated that the excess relative risk per milligray (mGy) of ionizing radiation was 0.036 for leukemia and 0.023 for brain tumors.

Compared with patients who were exposed to less than 5 mGy through CT scans, those whose red bone marrow was exposed to at least 30 mGy (mean, 50 mGy, the equivalent of about 5-10 head CTs) were 3.18 times as likely to develop leukemia in the 10 years after the first scan. Similarly, those whose brains were exposed to 50 to 74 mGy (the equivalent of about 2-3 head CTs) were 2.82 times as likely to develop brain tumors.

The investigators do not know whether the findings also apply to adults or only to radiosensitive children. Similarly, most (>80%) of the study participants were white, so they don’t know whether the results apply to other ethnic populations.

The researchers were quick to point out that the absolute risks of these cancers occurring after CT is small and that the benefits of CT in the setting of major head trauma or life-threatening illness outweigh future cancer risks. They hope that CT manufacturers continue to try to reduce the dose of ionizing radiation received with each scan, and they implore physicians to use nonionizing diagnostic methods such as ultrasound and magnetic resonance imaging whenever possible.

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