CT scans implicated in 2% of cancers

Some experts question that estimate. Meanwhile, explaining the radiation risks of necessary imaging without unduly frightening patients remains daunting.

By Kevin B. O'Reilly, AMNews staff. Jan. 7, 2008.

A recent study estimates that between 1.5% and 2% of all cancers can be attributed to radiation from the 62 million computed tomography scans Americans get each year. The finding comes on the heels of earlier, similar risk estimates, and it has some experts saying physicians should think twice about ordering the test.

The review article in the Nov. 29, 2007, New England Journal of Medicine arrives at its estimate by examining the cancer effects on the 25,000 Japanese who survived the 1945 atomic bombs and received radiation doses equivalent to the x-rays emitted by several CT scans.

The authors, David J. Brenner, PhD, and Eric J. Hall, PhD, are professors at the Columbia University Center for Radiological Research and have studied the cancer-causing effects of imaging for years. They write that the evidence of cancer risk from CTs is "reasonably convincing" for adults and "very convincing for children."

CTs deliver radiation doses many times that of other forms of radiography. An abdominal CT, for example, delivers at least 50 times more radiation to the stomach than an abdominal x-ray. While the authors estimate that the lifetime attributable cancer risk of a single head CT scan ranges from 0.08% for a neonate to practically zero for a 70-year-old, they write that "the concern about the risks from CT is related to the rapid increase in its use." The number of CTs that Americans get yearly has increased by 95% since 1980.

Arl Van Moore Jr., MD, chair of the American College of Radiology's Board of Chancellors, said that relying on Japanese atomic bomb survivors to gauge CT cancer risk is "like comparing apples and oranges" because they received a uniform, whole body dose all at once, while patients receive fractionated doses that only affect a single organ and are delivered over time.