Psychologist Jonathan Bricker, who conducts cancer prevention research at the Fred Hutchinson Cancer Research Center in Seattle, says he's not convinced. He's familiar with the UCSF letter and told me he's going to opt for pat downs when he flies from now on, which can total 15 times a year. "The pat down poses no health risks to me," he explains, whereas he's uncertain about the cumulative radiation exposure posed by the backscatter scanner.
I should point out that there's another type of full-body scanner being used in some airports that many experts prefer over the backscatter machine. It's called a millimeter wave scanner; it doesn't use X-rays, and as far as experts can tell it has "no known safety issues associated with it," says biophysicist David Brenner, director of the Center for Radiological Research at Columbia University Medical Center in New York City. Of the 385 imaging units at 68 U.S. airports, about half are millimeter wave scanners and half are backscatter machines. But the government isn't interested in only purchasing millimeter wave scanners, since it considers both technologies equally safe, says Kimball. "We want competition-driven innovation," he adds, which would be lost if only one company was given a lucrative government contract.
The TSA has a list of airports that currently employ the new imaging technology, but the list doesn't indicate which airport has which type of scanner. For that information, passengers would need to ask airport security personnel directly.
Overall, an individual's risk of going though a full-body scanner once or twice a year "is miniscule," Brenner says. Still, the risk could be more significant, he says, for pilots, flight attendants, and other frequent fliers who pass through security hundreds of times a year, upping their cumulative radiation exposure. Like the UCSF scientists, Brenner adds that he'd like to see "more independent analyses of the radiation doses involved," since "there is fairly convincing evidence" that the FDA is underestimating the radiation dose delivered by these scans. The U.S. Airline Pilots Association has voiced concerns about radiation exposure from the scanners and has asked the TSA to exempt pilots from the scans. For now, those who seldom travel through airports shouldn't be too concerned about radiation exposure from backscatter scanners. Frequent flyers, though, might want to follow Bricker's lead and opt for pat downs if they aren't too averse to them—at least until more is known about the radiation risks.