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Childhood CT scans increases cancer risk

Robin Wulffson MD's picture
CT scan, computerized tomography, leukemia, brain cancer, radiation

A computerized tomography (CT) scan is a useful diagnostic tool commonly used today. However, it does result in exposure to ionizing radiation at a higher level than many other diagnostic procedures.

For example, a CT scan of the abdomen and pelvis delivers 100 times the radiation dosage of a chest X-ray. Ionizing radiation increases risk of a cancer that may not develop until years after the procedure; in addition children are more sensitive to ionizing radiation than adults. Thus, exposure in childhood is much more of concern than comparable exposure to a senior citizen. British researchers have reported that a childhood CT scan significantly increase the risk of leukemia and brain cancer. They published their findings online in The Lancet.

In view of the well-established fact that children are more radiosensitive than adults, the authors designed a study to evaluate the increased risk of leukemia and brain tumors following a CT scan in children and young adults. The retrospective study included patients younger than 22 years of age without previous cancer diagnoses who were first examined with CT in National Health Service (NHS) centers in England, Wales, or Scotland between 1985 and 2002.

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The investigators obtained data for cancer incidence, mortality, and loss to follow-up from the NHS Central Registry from January 1, 1985 through December 31, 2008. They estimated absorbed brain and red bone marrow doses per CT scan in milligray (mGy) and assessed the increased risk of leukemia and brain tumors cancer. (The mGy is a measure of radiation exposure. The average radiation dose from an abdominal X-ray is 1.4 mGy, that from an abdominal CT scan is 8.0 mGy, that from a pelvic CT scan is 25 mGy, and that from a selective CT scan of the abdomen and the pelvis is 30 mGy.) To avoid the inclusion of CT scans related to a cancer diagnosis, follow-up for leukemia began two years after the first CT scan, while follow-up for brain tumors began five years after the first CT.

The researchers found that during follow-up, 74 of 178,604 patients were diagnosed with leukemia and 135 of 176,587 patients were diagnosed with brain tumors. They found a positive association between radiation dose from CT scans and leukemia as well as brain tumors. Compared with patients who received a dose of less than 5 mGy, patients who received a cumulative dose of at least 30 mGy had a 3.18 times higher risk of leukemia and a 2.82 times higher risk of brain cancer.

The authors concluded that the use of CT scans in children to deliver cumulative doses of about 50 mGy might almost triple the risk of leukemia 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 leukemia and one excess case of brain tumor per 10,000 head CT scans is estimated to occur. They stressed that,, 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 considered if appropriate.

Limitations of the study include lack of documentation regarding the reason for the CT scan and other clinical variables.

Reference: The Lancet