Radiation doses from CT (computed tomography) scans are so much higher than everyone thought that they could be causing cancer, a new study has discovered. In some groups, one in 80 people who have a routine CT scan will go on to develop cancer from the radiation, researchers at the University of California at San Francisco found. The risk seems to be greater among young people, and in women. They also discovered an enormous variation in the radiation levels being emitted by the scanners, and they noted up to a 13-times difference, depending on the type of CT procedure. The radiation from a single CT scan is equivalent to 74 mammograms or 442 chest x-rays, the researchers found, and yet the scan is routinely and regularly used, even when it is not necessary. (Source: Archives of Internal Medicine, 2009; 169: 2078-86).