Four university scientists waited six months for a government reply to a letter they wrote in the spring of 2010, warning government officials about health risks associated with full body scanners used by TSA. After all that waiting, the reply they eventually received seems to raise more questions than it answers.
The April Letter
In the April letter, the scientists raised a number of health concerns and unanswered questions about the effect of full-body exposure to radiation on air passengers. The letter calls out special concerns related to specific population groups, like the elderly, children, pregnant women, cancer patients, HIV positive travelers, and men.
For example, the scientists point out that the “real dose” of X-ray exposure to the skin of an air passenger being scanned is significantly higher than the dose emitted during a chest X-ray. The comparison is significant because the pro-TSA media had defended the scanners by comparing them to the dose emitted during a chest X-ray.
Another concern of the scientists was that genuine, authentic safety data about the scanners does not exist – that is why TSA has to cite studies based on chest X-ray machines. The scientists also identified eight specific areas of concern, including the risk of sperm mutagenesis, from scanning the body without protecting the testicles, and the risk of birth defects from scanning the body without protecting the uterus.
Finally, the scientists’ letter addressed potential risks from hardware and software failures – glitches that could zap a traveler with an intense ray to a single point on the skin, low resolution images that could cause a TSA worker to scan the groin are more slowly in an enhanced search for contraband, or hardware malfunctions that could expose everyone in the terminal to radiation.
The letter was authored by internationally known cancer specialist and UCSF professor Marc Shuman, M.D., and three UCSF professors of biochemistry and biophysics, David Agard, Ph.D., John Sedat, Ph.D. (Emeritus), and Robert Stroud, Ph.D. The scientists sent the letter to the head of the President’s Office of Science and Technology Policy, Dr. John P. Holdren, himself a distinguished former Harvard professor and highly regarded expert in science and technology.
The October Reply
The tardy reply to the letter was a joint missive from deputy-level directors at two different federal agencies: the Food and Drug Administration (FDA) and the TSA, to Dr. Holden. The letter, dated October 12, 2010, and sent to the scientists a few weeks later, appears to address the scientists’ concerns with conclusions based on existing studies, many conducted between 1998 and 2003, and some as recently as 2009.
Upon scrutiny, however, at least one of the studies cited in the reply seems to support the scientists’ concerns. For example, the reply criticizes the scientists for assuming that screening could result in doses of radiation to the skin and other organs that are “orders of magnitude higher than the effective dose per screening.” In fact, the study cited in footnote 20 of the reply shows that actual exposure to some organs could be lower than or significantly higher than the effective dose per screening.
Higher radiation exposure to the testicles
Although the reply implies that the scientists were mistaken in assuming that actual radiation could be higher than the effective dose, Footnote 20 cites a study that proves just that. Footnote 20 reports that dose modeling has shown that radiation exposure to the testicles is 276 percent higher than the effective dose delivered by the device. A screening that delivers an effective dose of .25 units delivers an estimated dose of .69 units to the testes, an increase of 276 percent.
What’s more, the 276 percent estimate applies to chest X-ray machines – products that the FDA and TSA say have a “very similar” output to the output of TSA scanners. They cannot cite to studies done with TSA scanners because no data exists about the TSA scanners. No one knows the “order of magnitude” of the effective dose of radiation that a TSA scanner delivers to a passenger’s testicles.
The reply went on to address hardware concerns by citing hardware production standards that are designed to shut down the primary beam in the event of a system problem. Critics note that the reply implies that the market will decide which manufacturers do the best job of meeting specifications, without addressing the consequences of equipment failure.
As for the possibility that scanners could slow down on the groin, the FDA/TSA reply points out that current scanners cannot be adjusted. If enhanced scanners were to be developed in the future that could slow down, then “the point of measurement to determine the dose per screening would also changed.” The reply did not address how the change would be calculated or how manufacturers would solve the technical challenge of delivering higher resolution images while lowering radiation exposure levels.
In summary, last spring four independent, credible scientists reported genuine health concerns to the Office of science and Technology over the body scanners TSA uses to scan travelers in some US airports. Six months later, the FDA and TSA replied to the letter, dismissing the scientists’ concerns by citing manufacturing standards for scanning equipment and studies that were mostly based on chest X-ray machines. Limited data exists about the scanners used by TSA.
This exchange of letters between the scientists and the bureaucrats demonstrates that ample evidence exists to argue the case for or against use of TSA scanners in US airports. Each side calls the others’ argument junk science. The only sure thing about TSA’s use of full body scanners is that the debate about their safety will be fervid and long-lived.
