AIM: Do the math--airport rad dose risks dont add up
Full-body scanners found in most U.S. airports do not appear to be a significant radiation threat to air travelers, according to article published online in the Archives of Internal Medicine on March 28. The radiation exposure incurred during a full-body scan is a fraction of the exposure incurred during air travel, the authors reported.

“Thus far, the TSA [Transportation Security Administration] has deployed 486 scanners in 78 airports in the U.S., with an estimated 1,000 scanners to be deployed by the end of 2011,” shared Pratik Y. Mehta, BS, of the University of California, Berkeley, and Rebecca Smith-Bindman, MD, of the University of California, San Francisco.

The level of radiation emitted by these scanners is so low that it is not known whether there is a potential for harm; however, the authors noted “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.”

Mehta and Smith-Bindman compared the radiation delivered by the scanners to “an amount of radiation equivalent to three to nine minutes of the radiation received through normal daily living.” At low doses, cells rapidly repair the biological damage caused by radiation, the authors pointed out.

The authors estimated the potential risks of the radiation in airport scanners by quantifying the actual exposure and estimated the risk of exposure to radiation among air travelers in three groups: all flyers, frequent fliers and frequent fliers who are five-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.

Mehta and Smith-Bindman acknowledged that the science of extrapolating risk from higher-dose studies is “questionable and may be inappropriate.” In addition, the scanners concentrate dose to the skin, and no mathematical model has been developed to quantify the relationship between skin exposure and risk of skin cancer.

Despite the uncertainties, 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 0.1 uSv (microsievert) for the estimates. Actual radiation exposure from the scanners ranges from 0.03 to 0.1 uSv per scan, and air travel itself exposes travelers to approximately 0.04 uSv per minute of flight time, with a six-hour flight exposing a passenger to approximately 14.3 uSv of radiation.

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 noted 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 estimated that for every 2 million five-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,” the authors concluded.