Those full-body CT scans advertised at some health care centers may be delivering as much radiation as a low-dose atomic bomb, according to a new study. And that means people who get them could be raising their cancer risk, researchers from Columbia University report in the journal Radiology (Vol. 232, No. 3:735-738).

"The radiation dose from a full-body CT scan is comparable to the doses received by some of the atomic bomb survivors from Hiroshima and Nagasaki, where there is clear evidence of increased cancer risk," said David J. Brenner, PhD, D.Sc, lead author of the study and professor of radiation oncology and public health at Columbia University in New York.

He calculated that a 45-year-old person who has one full-body CT scan would have a lifetime risk of dying from cancer because of that radiation of about 1 in 1,200. But if that same person got a scan a year for 30 years (30 total scans), his risk of dying from cancer because of that radiation would increase to almost 1 in 50. However, a person's overall risk of dying from cancer is affected by many things, including age, smoking and other lifestyle habits, and genetics.

The study is sure to add fuel to the already hot controversy over full-body computed tomography scans.

The scans are marketed as a way for healthy people to find diseases like lung cancer or colon cancer before symptoms become apparent. But many experts say there's little evidence the scans actually work as a screening tool. No studies have been done to determine whether screening for disease in this way actually saves lives or improves people's outcomes.

"Leading scientific and medical organizations not only do not endorse full-body CT screening, but also caution against use of this test," said Robert Smith, PhD, director of cancer screening for the American Cancer Society.

For one thing, the scans may show a person has nothing wrong when in fact there is disease present. Because the patient thinks he's healthy, he may not get other screening tests that could find his disease early.

Another problem: The scans may wrongly identify normal areas as suspicious. To know for sure, though, the patient must undergo costly and potentially risky invasive procedures to get a definitive diagnosis.

The risk of too much radiation exposure is just one more reason not to recommend the tests, said Smith.

"This is a genuine concern, but a comparatively minor concern" compared to the other reasons to avoid full-body CT screening, Smith said.

However, that doesn't mean people should avoid CT scans when they're needed to diagnose a disease.

"The risk-benefit equation changes dramatically for adults who are referred for CT scans for medical diagnosis," Brenner said. "Diagnostic benefits far outweigh the risks."