But backscatter machines do function differently than most medical imaging systems, and some scientists say the information presented by the government may have underestimated the safety risks. Glenn Sjoden, a professor of nuclear and radiological engineering at the Georgia Institute of Technology, says comparing 1,000 backscatter X-rays to one chest X-ray (as the government’s estimates do) doesn’t accurately describe of the risk.
When a person is exposed to higher-energy radiation, it passes through the body delivering a similar dose of radiation throughout. The energy of the backscatter X-rays is lower than in a chest X-ray, which means it stops at the skin. “It is not a good analogy,” says Sjoden. “Because of the physics being applied in the backscatter devices, your whole body is not getting the dose.” Instead, he says, it’s mostly the skin getting the dose.
Sjoden says it should be possible to measure a full body dose of radiation from a backscatter machine and extrapolate the dose given to the skin. Both he and the USCF scientists are also concerned that backscatter machines could accidentally give someone a higher dose of radiation, or that a TSA employee could increase the dose to get a better view of a person.
However, Sjoden isn’t as worried that the estimated exposure is dangerously wrong. “You would have to be a heavy traveler to accumulate a large dose.”
But Sjoden still questions whether enough studies have been done to determine the risk across the population, especially since children, the elderly, and some people with genetic predispositions to cancers are more sensitive to the effects of radiation.
“My initial gut reaction is, that’s a lot of work to do,” said Sjoden. “Whether or not it’s been thoroughly investigated, I was not able to tell from what’s out there.”
Ed Nickoloff, professor of radiology at Columbia University and chief hospital physicist at Columbia University Medical Center, says the data isn’t yet clear either way. “At this point, until I knew more information, I’d tell people to take the pat-down,” he says.