If you're healthy and your doctor suggests CT scans for preventive screenings, question it and get a second opinion.

Doctors and patients should think more carefully about CT scans, new research suggests.

RODALE NEWS, EMMAUS, PA—CT scans are important diagnostic tools that can detect cancer tumors as small as an eighth of an inch in diameter. But overuse of the machines could actually be hurting us in the form of excess radiation and an increased cancer risk, according to studies in this month's Archives of Internal Medicine journal.

"The articles in this issue make clear that there is far more radiation from medical CT scans than has been recognized previously, in amounts projected to cause tens of thousands of excess cancers annually," writes Rita F. Redberg, MD, professor of medicine at the University of California–San Francisco. "Also, as these scans have become more sensitive, incidental findings lead to additional testing, and often more radiation, biopsies, and anxiety."

THE DETAILS: To figure out how much radiation medical imaging delivers in order to balance the risk-benefit ratio, researchers looked at 1,119 patients undergoing 11 common types of diagnostic CT scans at four different facilities last year. Researchers looked at hospital records to figure out radiation dosage from each scan and then calculated estimated lifetime risks of cancer that could be attributed to the scans.

The researchers found that radiation varied among machines and area of the body scanned. For instance, a CT abdomen and pelvis scan used about 15 times the amount of radiation used in a head CT scan. Researchers determined CT scan technology used for coronary angiography, a heart scan, at age 40 would result in one in 270 women and one in 600 men developing cancer down the line as a result of the scan. For a lower-radiation-dose CT head scan, an estimated one in 8,100 women and one in 11,080 men who received the scan at age 40 would develop cancer in a lifetime. The risk is doubled for 20-year-old patients, and for 60-year-olds, they are about 50 percent lower.