A special article estimating the potential risk from full-body scanning machines found in most U.S. airports suggests that there does not appear to be a significant radiation threat to air travelers. The was article posted online today and will appear in the July 25 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

"Thus far, the TSA has deployed 486 scanners in 78 airports in the United States, with an estimated 1,000 scanners to be deployed by the end of 2011," the authors write as background information in the article. The levels of radiation emitted by these scanners is so low that it is not known whether there is a potential for harm, however the authors note "the cancer risks merit consideration given there are 750 million passenger enplanements a year, and even a small risk per person could potentially translate into a significant number of cancers."

The authors state that the scans "deliver an amount of radiation equivalent to three to nine minutes of the radiation received through normal daily living." When compared to other sources of radiation, the authors note: "An individual would have to undergo more than 50 airport scans to equal the exposure of a single dental radiograph, 1,000 airports scans to equal the exposure of a chest radiograph, 4,000 airport scans to equal the exposure of a mammogram, and 200,000 airport scans to equal the exposure of a single abdominal and pelvic computed tomographic scan."

Pratik Mehta, of the University of California, Berkeley, and Rebecca Smith-Bindman, M.D., of the University of California, San Francisco, estimated the potential risks of the radiation in airport scanners by quantifying the actual exposure.

The authors estimated the risk of exposure to radiation among air travelers in three groups: all flyers, frequent fliers and frequent fliers who are 5-year-old girls. The last group was chosen because children are more sensitive than adults to the effects of radiation, and existing models could be used to estimate the risk of breast cancer from the airport scanners. For the estimates, the authors assumed that all passengers undergo a full-body scan for each trip, that 100 million unique passengers will take 750 million flights in a year and assumed the exposure of the scans is 0.1µSv (microsievert).

For all flyers, the authors estimate that of the 750 million flights taken per year by 100 million passengers, six cancers over the lifetime of these individuals could result from the airport scanners. However they note that, "these six cancers need to be considered in the context of the 40 million cancers that would develop over the course of their lifetime due to the high underlying cancer incidence."

Among frequent fliers who fly 60 hours a week, four additional cancers could occur from the scanners, however these need to be considered in the context of the 600 cancers that would occur from the radiation received from flying at high elevations and the 400,000 cancers that would occur over the course of their lifetime. The authors also estimate that for every two million 5-year-old girls who travel one round-trip a week, one additional breast cancer would occur from the scans, however 250,000 breast cancers will occur in this group over their lifetimes owing to the 12 percent lifetime incidence of breast cancer.

"Based on what is known about the scanners, passengers should not fear going through the scans for health reasons, as the risks are truly trivial. If individuals feel vulnerable and are worried about the radiation emitted by the scans, they might reconsider flying altogether since most of the small, but real, radiation risk they will receive will come from the flight and not from the exceedingly small exposures from the scans." However the authors also note that, "it would seem prudent for the TSA to permit additional testing to verify the safety of the devices."

Arch Intern Med. Published online March 28, 2011. doi:10.1001/archinternmed.2011.105.