Radiation from CT scans linked to cancers, deaths

By Liz Szabo, USA TODAY

CT scans deliver far more radiation than has been believed and may contribute to 29,000 new cancers each year, along with 14,500 deaths, suggest two studies in today's Archives of Internal Medicine. One study, led by the National Cancer Institute's Amy Berrington de Gonzalez, used existing exposure data to estimate how many cancers might be caused by CT scans.

Another study in the journal suggests the problem may even be worse. In that study, researchers found that people may be exposed to up to four times as much radiation as estimated by earlier studies. While previous studies relied on dummies equipped with sensors, authors of the new paper studied 1,119 patients at four San Francisco-area hospitals, says author Rebecca-Smith Bindman of the University of California-San Francisco. Based on those higher measurements, a patient could get as much radiation from one CT scan as 74 mammograms or 442 chest X-rays, she says.

Young people are at highest risk from excess radiation, partly because they have many years ahead of them in which cancers could develop, Smith-Bindman says. Among 20-year-old women who get one coronary angiogram, a CT scan of the heart, one in 150 will develop cancer related to the procedure.

Not all doctors agree about those risks. Scientists have not yet determined whether low doses of radiation actually increase cancer risk or whether the risk rises only after exposure levels reach a certain threshold, says James Thrall, chairman of the American College of Radiology.

He says it's also tricky to compare cancer rates between people who have had CT scans with those who haven't. People undergoing scans may have underlying health problems that predispose them to cancer, he says.

In many cases, CT scans can be lifesaving. In other cases, there's no evidence a CT scan is really better than other approaches, Smith-Bindman says. Up to one-third of all CT scans are unnecessary, according to an accompanying editorial by Rita Redberg, also of UCSF.

Doctors sometimes order CT scans for convenience because they don't have access to results at another facility, says Rosaleen Parsons, chair of diagnostic imaging at Philadelphia's Fox-Chase Cancer Center, who wasn't involved in the new studies.

She suggests that patients keep their medical records and ask doctors about alternatives that don't involve radiation exposure.

She says patients also should ask if a facility has been accredited by the American College of Radiology.