The danger from radiation exposure for any given person walking through a backscatter X-ray machine at an airport is low, but there’s controversy over whether the aggregate risk to the traveling population is high enough to warrant regulatory change, according to two new research papers. The papers come on the heels of an admission Tuesday by the Transportation Security Administration that their X-ray machines might emit up to 10 times more radiation than previously thought — although they maintain the machines are safe. Traditional X-ray machines rely on electromagnetic radiation to penetrate objects and report back the presence of solid objects, which absorb the radiation more easily. Backscatter X-ray machines detect the radiation that reflects off objects, allowing it to “see” a wider range of objects than traditional X-rays.
Airports have recently begun adopting backscatter X-ray machines as a way to improve security. In addition to privacy worries over backscatter X-ray’s detailed body imaging, concerns over whether the radiation exposure from the machines presents a health hazard have been mounting.
Last year, several members of the National Academy of Sciences wrote a letter to President Obama’s science advisor John Holdren arguing that the machines present a greater danger than their manufacturers claim because the manufacturers miscalculated the level of radiation absorbed into the bones and skin.
Other experts disagreed with that assertion. TSA commissioned a number of independent safety examinations of the machines in late 2010 and found the machines to be acceptably safe.
Two new articles by radiation experts appearing in the April edition of the journal Radiology come down on both sides of the debate.
In one paper, David Brenner, director of the Center for Radiological Research at Columbia University Medical Center in New York City, argues that while the risk to individuals is small, the sheer number of people passing through backscatter X-ray machines every day is enough to raise concerns about the collective risk to public health.
Based on estimates of usage and numbers of travelers, as many as 1 billion people could be scanned with backscatter X-ray machines this year, Brenner said. Even if the risk to any one individual person is scant, it’s very possible that some of them could develop cancer as a result of radiation exposure from the machines.
Because the risk goes up for frequent fliers such as airline personnel and those whose jobs require frequent travel, Brenner said he advises these people to opt for pat-downs rather than an X-ray machine screening.
In the other paper, David Schauer, director of the National Council on Radiation Protection and Measurements in Washington, D.C., argued that the risk presented by radiation from the machines pales in comparison to the risks we take every day and that even at the aggregate -population level, it’s not an issue worth worrying about. Still, he said, the machines should be used as sparingly as possible and.strict regulation of the technology should be in place to keep the risks low.
Schauer said that the real issue comes down to whether the threat from terrorism justifies exposing travelers to backscatter X-ray radiation and whether that technology is capable of identifying dangerous items — questions only TSA can answer.
“You have to look at the threat and whether [this technology] is the best way to deal with it,” Schauer said. “The good must outweigh the harm.”
In a congressional hearing for the Subcommittee on National Security Wednesday, TSA assistant administrator for operational process and technology Robin Kane told congress that the risk posed by terrorists seeking to sneak aboard non-metallic explosives on their bodies justifies the use of advanced imaging technology like backscatter X-ray machines.
“Advanced imaging technology … addresses a broad range of threats, many of which cannot be addressed by older technologies like metal detectors,” she said,
However, experts questioned whether backscatter X-ray technology is the only option.
Brenner agreed that “if there were no feasible alternatives to X-ray backscatter scanners, it could certainly be argued that such population risks would be more than balanced by the associated benefits of reducing the risk of a terrorist event.”
However, both Brenner and Schauer believe that an alternative to the backscatter X-ray machine known as a millimeter wave scanner is safer and preferable.
