As it increases the risk of developing cancer in children exposed to CT?

What is the excess risk of cancer after CT scan in children? Recently The Lancet published a study in which a positive association between radiation dose from CT scan and leukemia and brain tumor was found. Data came from this retrospective cohort study in UK of almost 180,000 patients younger than 22 years of age without previous cancer diagnoses who were first examined with CT in some National Health Service (NHS) centres. Follow-up for leukemia began 2 years after the first CT and for brain cancer 5 years after the first CT in order to avoid inclusion of CT scans related to cancer diagnosis. A positive association between radiation dose from CT scans and leukemia and brain cancer was found. Compared with patients who received a dose of less than 5 mGy, leukemia incidence was about three times higher in patients who received a cumulative dose of at least 30 mGy and for brain cancer in patients who received a dose of 50-74 mGy. Since these cancers are relatively rare, the cumulative absolute risks are small. 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 ionizing radiation, should be taken in consideration if appropriate.