As few as two CT scans of the head in childhood can triple the risk of developing brain tumors, while five to 10 such scans can triple the risk of leukemia, British researchers reported Wednesday. The absolute risk of developing the cancers remains small, but the study illuminates the dangers of unnecessary use of X-ray imaging in diagnosis.
The development of CT (computed tomography) scanning was one of the major developments of 20th century medicine because it allowed physicians to look inside the body more accurately than a conventional X-ray. But it also provides a much higher dose of radiation than a conventional X-ray. Based on extrapolations of data from survivors of the atomic bomb attacks in Japan at the end of World War II, some scientists have warned that such scans could increase the risk of cancer, especially in children, whose growing bodies are more sensitive to the effects of radiation. Others, however, have dismissed this as speculation because of the differences between bomb radiation and CT scans. In particular, a bomb affects the whole body, while a CT scan is focused on a small area. But there have been no previous epidemiological studies examining the risks.
A team headed by epidemiologists Mark S. Pearce and Dr. Alan W. Craft of Newcastle University studied nearly 180,000 children who underwent at least one CT scan between 1985 and 2002 in the radiology departments of 70% of the United Kingdom's hospitals. They estimated the dose of radiation absorbed in each scan, then linked the data to cancer incidence and mortality reports in the UK National Health Service Registry and calculated excess incidence of brain tumors and leukemia.