Your readers should be aware that the increased fatal cancer risk posed by annual whole-body CT scans, although still quite high, is in fact almost five times lower than that stated in this article, which says that annual scans from age 45 to 75 would increase a person’s lifetime risk of dying from cancer by 1.9 percent. By my calculation, current risk is 48 to 60 cancer deaths for every 240 people, so a 1.9 percent increase would mean an extra 0.9 to 1.1 deaths: 1 extra death per 240 people. While this increased risk is disturbingly high, it is 4.8 times lower than the risk quoted in the story, 1 extra death for every 50 people.

Todd P. Silverstein
Willamette University
Salem, Ore

Study coauthor David J. Brenner of Columbia University says that the 1 extra death for every 50 people having full-body CT scans is correct. This would increase a person’s chance of dying from cancer from 23 percent to 25 percent. As presented in Science News , the 2 percent was ambiguous, he says, so it’s not surprising that Silverstein misinterpreted it as a relative risk factor, in which case the cancer mortality would have gone up only to 23.5 percent .—D. Parsell