Accumulated CT radiation dose triples pediatric cancer risk

By Lynda Williams

The use of computed tomography (CT) scans should be minimized in children, recommend researchers who have found a significantly increased risk for malignancy with repeated imaging.

"Because these cancers are relatively rare, the cumulative absolute risks are small," say Mark Pearce (Newcastle University, UK) and co-authors, who estimate that over 10 years one excess case of leukemia and brain tumor each will occur per 10,000 head CT scans performed in patients aged less than 10 years.

Nevertheless, they emphasize in The Lancet: "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."

The team collated cancer incidence and mortality data for patients aged under 22 years who underwent CT imaging in National Health Service centers in England, Wales, and Scotland between 1985 and 2002.

The patients included in the study had no previous history of malignancy. To avoid inclusion of CT scans related to cancer diagnosis, patients were followed up for leukemia and brain tumors 2 and 5 years after initial imaging, respectively, the team explains.

Overall, 74 of 178,604 patients (283,919 scans) were diagnosed with leukemia, and 135 of 176,587 patients (279,824 scans) were diagnosed with a brain tumor.

The researchers calculated mean dose to the red bone marrow and brain tissue, and discovered a significant and positive correlation between CT scan radiation dose and the risk for leukemia and brain tumors, with an excessive relative risk (RR) of 0.036 and 0.023, respectively.

When compared with patients with less than 5 mGy dose of radiation, the RR for leukemia for patients with a cumulative dose of 30 mGy or above (average dose 51.13 mGy) was 3.18. For patients with a cumulative dose of 50‑74 mGy (average dose 60.42 mGy), the RR for brain tumor was 2.82.

"The immediate benefits of CT outweigh the long-term risks in many settings and because of CT's diagnostic accuracy and speed of scanning, notably removing the need for anaesthesia and sedation in young patients, it will remain in widespread practice for the foreseeable future," observe Pearce et al.

"Further refinements to allow reduction in CT doses should be a priority, not only for the radiology community but also for manufacturers."

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