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.
One study 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 more than 1,000 patients at four hospitals.
Based on their measurements, a patient could get as much radiation from one CT scan as 74 mammograms or 442 chest X-rays.
Young people are at highest risk from excess radiation, partly because they have many years ahead of them in which cancers could develop. 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.