--Relatively high radiation exposure
--High cost that insurance will not cover

These same critics suspect that whole-body scans also produce:
--A heightened risk of "false positives" that can lead to needless surgeries and potential complications

--Unnecessary medical expenses for insurance companies, which may pass these costs onto consumers

Lack of scientific data on the procedure

Advertisements for full-body scans typically contain testimonials of patients who found diseases early and say the procedure saved their lives.

"But such data is anecdotal," says John Boone, a UC-Davis medical physicist and chief draftsman of the AAPM policy statement on CT body scanning. Boone says that the lack of scientifically rigorous studies on whole-body screening scans suggests that individuals should think long and hard before considering having such an exam or giving one as a gift.

"These are hard studies to do," Gould acknowledges. A rigorous scientific study of the procedure might be problematic for several reasons, including the ethical issue of exposing low-risk individuals to relatively high amounts of medical radiation. But researchers can potentially explore simpler questions about whole-body scans, he says, and no one is doing this.

Radiation concerns

Radiation exposure is AAPM's main concern. Whole-body scans expose a person to "significant radiation exposures" for a diagnostic medical procedure, in the words of the AAPM statement. In general, medical professionals avoid exposing patients to radiation, unless the potential benefits outweigh the small risk from the radiation. But the benefits of whole-body scans are unknown, since no scientific data on this question exist, points out medical physicist Ralph Lieto, the chair of the AAPM Radiation Protection Committee, which wrote the statement on whole-body scanning. The risk that x-rays damage DNA in healthy cells and cause cancer in later years increases with dose.

Small as this risk may be, whole-body CT scans deliver significantly higher radiation doses than other x-ray procedures. While a standard chest x-ray takes a single snapshot of the body, a CT scanner takes multiple snapshots as it rotates around the patient. What's more, the full-body scan takes pictures along the length of the body, rather than in just a targeted region.

Unproven benefit

As a result, a typical whole-body CT scan may deliver an "effective" radiation dose about 250 times greater (15 millisieverts) than a patient receives in a chest x-ray, estimates AAPM president Gould. "Effective dose" is a measurement of the risk that radiation poses to the body. It takes into account the amount of radiation delivered to each body region and each region's sensitivity to radiation.

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