Take a risk

Science News, Nov 6, 2004 by Todd P. Silverstein, D. Parsell

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 "Scanning Risk: Whole-body CT exams may increase cancer" (SN: 9/4/04, p. 149), 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 I 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.