Only a decade ago, many states prohibited X-raying a person for anything other than a medical exam. Even after 9/11, such non-medical X-raying remains taboo in most of the industrialized world. In July, the European Parliament passed a resolution that security “scanners using ionizing radiation should be prohibited” because of health risks. Although the United Kingdom uses the X-ray machine for limited purposes, such as when passengers trigger the metal detector, most developed countries have decided to forgo body scanners altogether or use only the millimeter-wave machines.
While the research on medical X-rays could fill many bookcases, the studies that have been done on the airport X-ray scanners, known as backscatters, fill a file no more than a few inches thick. None of the main studies cited by the TSA has been published in a peer-reviewed journal, the gold standard for scientific research.
Those tests show that the Secure 1000 delivers an extremely low dose of radiation, less than 10 microrems. The dose is roughly one-thousandth of a chest X-ray and equivalent to the cosmic radiation received in a few minutes of flying at typical cruising altitude. The TSA has used those measurements to say the machines are “safe.”
Most of what researchers know about the long-term health effects of low levels of radiation comes from studies of atomic bomb survivors in Hiroshima and Nagasaki. By charting exposure levels and cancer cases, researchers established a linear link that shows the higher the exposure, the greater risk of cancer.
Some scientists argue the danger is exaggerated. They claim low levels stimulate the repair mechanism in cells, meaning that a little radiation might actually be good for the body.
But in the authoritative report on low doses of ionizing radiation, published in 2006, the National Academy of Sciences reviewed the research and concluded that the preponderance of research supported the linear link. It found “no compelling evidence” that there is any level of radiation at which the risk of cancer is zero.
Radiation experts say the dose from the backscatter is negligible when compared to naturally occurring background radiation. Speaking to the 1998 FDA panel, Smith, the inventor, compared the increased risk to choosing to visit Denver instead of San Diego or the decision to wear a sweater versus a sport coat.
Using the linear model, even such trivial amounts increase the number of cancer cases. Rebecca Smith-Bindman, a radiologist at the University of California, San Francisco, estimated that the backscatters would lead to only six cancers over the course of a lifetime among the approximately 100 million people who fly every year. David Brenner, director of Columbia University’s Center for Radiological Research, reached a higher number — potentially 100 additional cancers every year.
“Why would we want to put ourselves in this uncertain situation where potentially we’re going to have some cancer cases?” Brenner asked. “It makes me think, really, why don’t we use millimeter waves when we don’t have so much uncertainty?”
But even without the machines, Smith-Bindman said, the same 100 million people would develop 40 million cancers over the course of their lifetimes. In this sea of cancer cases, it would be impossible to identify the patients whose cancer is linked to the backscatter machines.
How the scanners avoided strict oversight
Although they deliberately expose humans to radiation, the airport X-ray scanners are not medical devices, so they are not subject to the stringent regulations required for diagnostic X-ray machines.
If they were, the manufacturer would have to submit clinical data showing safety and effectiveness and be approved through a rigorous process by the FDA. If the machines contained radioactive material, they would have to report to the Nuclear Regulatory Commission.
But because it didn’t fit into either category, the Secure 1000 was classified as an electronic product. The FDA does not review or approve the safety of such products. However, manufacturers must provide a brief radiation safety report explaining the dose and notify the agency if any overexposure is discovered. According to the FDA, no such incidents have been reported.