Study: CT Scan Overuse Could Lead to Cancer Deaths

BY Lea Winerman  December 15, 2009 at 1:00 PM EDT

The millions of CT scans performed each year in the U.S. may be subjecting some patients to unnecessary cancer risk, and could lead to 29,000 extra cancer cases each year, according to two studies published Tuesday in the Archives of Internal Medicine.

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Doctors rely on detailed CT scan images to diagnose many injuries and diseases — including cancer — and the number of CT scans performed in the U.S. has more than tripled in the past two decades.

But CT scans, short for computed tomography, also expose patients to cancer-causing radiation. The scans combine data from multiple X-rays to give a clear, multifaceted views of internal organs. But those multiple images mean that patients are exposed to much more radiation than in a regular X-ray.

Some researchers have long suggested that doctors are overusing the diagnostic tool. The new studies quantify that risk and explore variations in radiation dosages.

The first study, an analysis of CT scan frequency and radiation risk, found that the 72 million CT scans performed in 2007 could lead to 29,000 cases of cancer and result in nearly 15,000 deaths.

”Physicians (and their patients) cannot be complacent about the hazards of radiation or we risk creating a public health time bomb,” Dr. Rita Redberg, editor of Archives of Internal Medicine, wrote in [an editorial](http://archinte.ama-assn.org/cgi/content/full/169/22/2049?home) accompanying the study. The [second study](http://archinte.ama-assn.org/cgi/content/full/169/22/2078#AUTHINFO) looked at actual radiation doses for 11 types of CT scans in more than 1,000 patients at four San Francisco hospitals. The researchers found that the doses varied wildly from hospital to hospital, and even for different patients at the same hospital — there was a more than 13-fold difference between the highest and lowest doses for the same type of scan. Those variations could be due to differences between machines, as well as the technique of the operators. But while there are reasons that some patients might need a higher dose than others, the variation is “much greater than widely considered acceptable,” the study authors say. The authors of the second paper also calculated some of the risks of CT scans. They found that approximately one in 270 women and one in 600 men who undergo heart CT scan at age 40 will develop cancer from that scan (women are more susceptible to radiation risk). Head scans, which involve less radiation, would cause an estimated 1 in 8100 women and one in 11,080 men who had one at age 40 to develop cancer. Still, the researchers say, CT scans do provide great medical benefit when used appropriately. “On an individual basis, if the scan is justified, then the benefits should outweigh the risks,” lead author Amy Berrington de Gonzalez, of the National Cancer Institute, [told the Wall Street Journal](http://online.wsj.com/article/SB126082398582691047.html). And not everyone agrees with the new study’s numbers. “I think it’s almost undoubtedly less than 29,000 [extra cancer cases]” Dr. James Thrall, Chairman of the American College of Radiology, [told National Public Radio](http://www.npr.org/templates/story/story.php?storyId=121436092&ps=cprs). But, he told NPR, at Massachusetts General Hospital, where he works, doctors who order a CT scan must check the reason against a computer program that offers an “appropriateness score” for the scan. That check has led the hospital to reduce it’s CT scan growth rate from 12 percent to 1 percent, Thrall says. “In one respect, it doesn’t matter whether it’s 29,000 or 1,000. There are opportunities for us in radiology to do all the good things we do using less radiation.”