Radiation exposure from a yearly full-body scan could dramatically increase the lifetime risk of cancer, researchers report in a new study.

The study was published Tuesday in the September issue of the journal Radiology. It found that a 45-year-old person who underwent one full-body computed tomography (CT) screening would have an estimated additional lifetime cancer mortality risk of about 0.08 percent, which would produce cancer in one of every 1,200 people.

But a 45-year-old who has annual full-body scans for 30 years would accumulate an estimated lifetime cancer mortality risk of 1.9 percent, or almost one in 50.

"Our research provides definitive evidence that radiation risk is associated with full-body CT scans," said David Brenner, a professor of radiation oncology and public health at Columbia University in New York City and lead author of the report.

"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."

The researchers considered the exposure only of low-dose A-bomb survivors in assessing the risk.

The calculated effective radiation dose (a weighted average over all relevant organs) from a full-body scan was compared with cancer mortality data from people who survived the 1945 atomic attacks on Japan with relatively low exposure.

A CT scan typically delivers much larger radiation doses to internal organs than do conventional X-rays. The effective dose of radiation delivered during a full-body CT exam is nearly 100 times that delivered from a typical screening mammogram.

Brenner and his team did the study as the radiology community continues to express concern about the popularity of body scans, which are offered to people with no particular symptoms in an effort to identify various diseases, including colon and lung cancer and blockages in heart arteries.

The scans, which actually just image from the neck to the thighs, reveal small abnormalities as tiny as hundredths of an inch wide, including old scars, cysts and other harmless masses along with dangerous structures.

Brenner noted that the risk assessment was done only for those who elect to have CT scans to check for hidden conditions. "The risk-benefit equation changes dramatically for adults who are referred for CT exams for medical diagnosis. In those cases, diagnostic benefits far outweigh the risks," he said.

The researchers also pointed out that different CT scanners produce different radiation doses, and that full-body-scan protocols are not standardized, so the average risk they calculated may vary with exposure at different scanning centers.

Health-insurance plans usually don't pay for the exams unless there's some other evidence that a patient is at high risk. But many people pay the $600 to $3,000 for each test to allay concerns about their health, and proponents of the test tout individual reports of patients who have found hidden disease early enough to save their lives.

But Brenner said no formal studies have demonstrated life-prolonging benefits from the testing. To the contrary, he said, "besides the radiation risks, elective full-body CT may provide false-positive findings where no disease exists. This typically involves more extensive testing, which is costly and stressful."