The scans are marketed as a way to catch cancer before symptoms begin, but the radiation from the scans themselves could cause cancer, the researchers said.

CT or computed tomography scans involve X-rays, but computer software and multiple angles produce a higher-quality image than the traditional flat X-ray.

The scans are not the same as magnetic resonance imaging or MRI scans, which do not expose the body to radiation.

Writing in the September issue of the journal Radiology, radiation oncologist David Brenner and colleagues at Columbia University in New York said whole-body CT scans pack a considerable radiation wallop.

"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," Brenner said in a statement.

They studied survivors who got low doses of radiation from the bombs, not those who got the highest doses.

The dose from a single full-body CT is only slightly lower than the mean dose experienced by some atomic bomb survivors, they said, and is nearly 100 times that of a typical screening mammogram.

A 45-year-old person who gets one full-body CT screening would have an estimated lifetime cancer death risk of approximately 0.08 percent, which would produce cancer in one in 1,200 people, they estimated.

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

The risk may be worth it for someone who knows he or she has a high probability of cancer, such as those with inherited genetic mutations or a family history of the disease, Brenner said.

Cancer is the second leading cause of death in the United States after heart disease and is expected to kill 550,000 people this year.