March 16, 2011 -- Full-body scanners have become the norm at airports around the country. Their use is aimed at keeping passengers safe. However, some experts worry that the most commonly used type of scanner heightens the risk of cancer because it emits low levels of ionized radiation. Two articles in the April issue of Radiology assess the risks.
The type of scanner in question scans travelers with what are called backscatter X-rays to detect objects hidden under clothing, such as nonmetallic explosives and weapons. Each time a passenger passes through one of these scanners, he or she is exposed to a tiny amount of radiation.
An individual’s risk of dying from cancer from such an exposure is estimated to be vanishingly small -- about one in 10 million for a trip involving two screening scans, writes David J. Brenner, PhD, DSc, director of the Center for Radiological Research at Columbia University Medical Center.
According to the FDA, which regulates X-ray devices, “There is no need to limit the number of individuals screened or, in most cases, the number of screenings an individual can have in a year.”
But Brenner believes the picture changes when you look at it from a larger, public health perspective, in which a billion travelers are scanned in the U.S. each year.
“In the present context, if a billion X-ray backscatter scans were performed each year,” writes Brenner, “one might anticipate 100 cancers each year resulting from this activity.”
Brenner also points to a heightened risk of cancer among children, which he says is five to 10 times higher than the risk to middle-age adults. Flight personnel, who pass through scanners hundreds of times each year, could also be at greater risk than the average traveler.
"Super frequent fliers or airline personnel, who might go through the machine several hundred times each year, might wish to opt for pat-downs,” Brenner says in a news release. “The more scans you have, the more your risks may go up -- but the individual risks are always going to be very, very small."
Appropriate Use of Scanners
David A. Schauer, ScD, CHP, author of the second article, acknowledges the risks of using backscatter X-ray scanners and focuses his paper on ways to ensure that such scanners are used appropriately.
“People should only be exposed to ionizing radiation for security screening purposes when a threat exists that can be detected and for which appropriate actions can be taken,” writes Schauer, executive director of the National Council on Radiation Protection and Measurements. “Any decision that alters the radiation exposure situation should do more good than harm.”
Schauer advocates for strong government regulation of the use of backscatter X-ray scanners to be certain that passengers are not exposed unnecessarily or to unsafe levels of radiation.
“When a government concludes that security screening of people with backscatter X-rays is justified,” he writes, “then regulatory control should be implemented.”
Like Schauer, Brenner believes that backscatter X-ray scanners are, on the whole, safe.
"As someone who travels just occasionally, I would have no hesitation in going through the X-ray backscatter scanner," Brenner says in a news release.
However, he argues against their use in favor of an alternative -- and equally effective -- type, known as a millimeter wave scanner, which does not involve ionizing radiation.
“Whatever the actual radiation risks associated with X-ray backscatter machines,” Brenner concludes, “a comparable technology that does not involve X-rays is a preferable alternative.”