Scanning risk: whole-body CT exams may increase cancer

Science News, Sept 4, 2004 by D. Parsell

In recent years, computerized tomography (CT) scanning has gone commercial, as healthy people pay to have their bodies scanned for general-health screening.

They may be doing themselves more harm than good. Reporting in the September Radiology, David J. Brenner and Carl D. Elliston of Columbia University say that people who routinely get CT body scans without medical cause are exposing themselves to low-dose radiation in amounts that may increase their risk of dying from cancer.

Despite its name, a typical whole-body scan targets just the torso. The procedure, which delivers the same amount of radiation as 30 chest X rays, usually costs hundreds of dollars. Increasing numbers of adults--usually affluent consumers dubbed the "worried well"--are repeatedly undergoing whole-body CT screening as part of routine medical checkups (SN: 9/20/03, p. 184).

On the basis of estimates of radiation doses received by different tissues in each scan, the Columbia researchers projected the incidence rate of cancer among healthy 45-year-old adults who have whole-body CT scans every year until age 75. The calculations suggest that such a practice would increase a person's lifetime risk of dying from cancer by 1.9 percent. Right now, an individual's chance of dying from cancer is between 1 in 4 and 1 in 5, Brenner notes. For every 50 people who have annual CT scanning for 30 years beginning at age 45, therefore, 1 would die of cancer induced by the accumulated radiation from the scans, the scientists say.

Any cancers that might stem from radiation in whole-body CT scanning aren't likely to appear for years or decades. So, the researchers turned to actual cancer-mortality data for survivors of the atomic bomb blasts in Hiroshima and Nagasaki. "Those survivors ... around 1.5 miles from the explosions received whole-body doses quite similar to those from a single [whole-body] CT scan," Brenner notes. Reports have shown that these bomb survivors have slightly higher odds of dying from cancer than do people in the overall population.

The study focused on cancer risk only for healthy adults who seek the high-tech procedure on their own. "The risk-benefit equation changes dramatically for those who are referred for [whole-body] CT exams for medical diagnosis," says Brenner. In such cases, he notes, "the diagnostic benefits far outweigh the risks."

Currently, there are no uniform operating guidelines for profit-oriented centers that offer whole-body CT screening, says Richard Morin of the Mayo Clinic in Jacksonville, Fla., who chairs the commission on medical physics of the American College of Radiology. That association has not accredited the procedure, he notes, and the Food and Drug Administration regulates levels of medical-radiation exposure for only mammograms.

Morin says that the new study by Brenner and Elliston is the best effort so far to determine potential cancer risks from radiation exposure in whole-body CT scans. "If a person is healthy, then there is an attendant risk of doing the procedure," he says, "and we know it's not zero."