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People who undergo numerous CT scans over a lifetime may have an elevated risk of developing cancer, a new study hints. CT scans are being increasingly used in nearly all areas of medicine because of their ability to provide detailed images of the organs, bones, soft tissues and blood vessels. But because they expose people to a relatively high dose of radiation compared with traditional X-rays, there are concerns about the long-term effects of having multiple CT scans.

For the new study, researchers at Brigham and Women's Hospital in Boston estimated the cumulative CT radiation exposure of more than 31,000 patients who'd had at least one scan over the previous 22 years.

Overall, 7 percent of the patients had had enough radiation exposure to raise their cancer risk by 1 percent over the U.S. norm, according to findings published in the journal Radiology.

For most people, the benefits of CT imaging outweigh the risks of radiation exposure, according to lead researcher Dr. Aaron Sodickson.

"CT is an excellent diagnostic tool of tremendous clinical value in many situations," Sodickson said in a news release from the journal.

"Individual decisions about its use should balance the expected clinical benefits against the potential cumulative risks of recurrent imaging."

Doctors may want to be more cautious about using the technology in people who've already had multiple CT scans in the past, according to Sodickson -- especially if those previous scans have turned up nothing.

"This scenario," he noted, "may result in a combination of high cumulative risk with low clinical benefit."

Sodickson and colleagues analyzed data from 31,462 patients who'd undergone CT scans at Brigham and Women's or the Dana-Farber Cancer Center in 2007. Overall, one-third had undergone five or more CT examinations over the previous 22 years, while 5 percent had had anywhere between 22 and 132 scans.

Fifteen percent had been exposed to a radiation equivalent of 1,000 traditional chest X-rays, according to the researchers.

They say that there are a number of potential ways to help protect patients from the radiation exposure of multiple CT scans. Technical advances, for example, could lower the radiation dose delivered with each exam, while alternative types of imaging, such as MRI, could be used for some patients.

Source: Reuters Health