U.S. study weighs lifetime risks from CT scans

CHICAGO (Reuters) - As many as 7 percent of patients from a large U.S. hospital system had enough radiation exposure from CT scans during their lifetime to slightly raise their risk of cancer, U.S. researchers said on Tuesday.

The finding is part of an effort to develop tools that help doctors assess a patient's overall cancer risk from exposure to computed tomography, or CT scans, researchers from Brigham and Women's Hospital in Boston told a meeting of the Radiological Society of North America in Chicago.

CT scans -- a souped-up X-ray machine that rotates around the body taking different images -- speed diagnosis of illness and injuries, and are routinely used to track the advance of cancer. But a number of recent studies have raised alarms about the potential cancer risks from the radiation.

"A lot of this discussion has been very theoretical in the past. What we have been trying to do is to develop the tools to say what is a patient's level of risk based on a history of CT scans," Dr. Aaron Sodickson, who led the study, said in a telephone interview.

Sodickson and colleagues studied all patients who had a CT scan in 2007 at Brigham and Women's Hospital, or at the Dana-Farber Cancer Institute, both affiliates of Harvard Medical School in Boston.

They checked on prior CT scans from a database that includes 22 years of patient history and calculated overall radiation exposure based on the type and location of the scan to determine a lifetime risk.

"We found about 7 percent of our patients did have a cancer risk that increased by 1 percent of what we would expect as a baseline cancer rate," Sodickson said.

"The next step is to use this information to improve our patient care and make better decisions."

Sodickson hopes to develop a computer alert that informs a doctor of a patient's individual cancer risk based on his or her history of CT scans. He said the alert would pop up when the doctor enters an order for a CT scan.

"Within the next year we are planning to roll this out at the Brigham to help people make better decisions. That is where we are going with this," he said.

Sodickson said for most people, the radiation exposure from CT scans is well worth the risk. But for cancer patients, who get repeated CT scans, that could raise their risk of another tumor.

"If you have a patient and you've cured their cancer, but you keep scanning them over and over to make sure the cancer is still gone, you raise their risk of a second cancer," he said.

A typical CT scan can deliver 50 to 100 times more radiation than a conventional X-ray, depending on the site being examined and the age and brand of the machine.

Some 62 million CT scans are done in the United States each year, and some studies estimate they may soon account for as much as 2 percent of all cancers.

(Editing by Maggie Fox)