Like the chaos unleashed by the mythical Pandora's box, the decision of the Transportation Security Administration (TSA)to begin installing advanced imaging technology in airports has led to the public being bombarded by discordant information about the new "full-body scanners." The two types of scanning technology being implemented are, primarily, "backscatter" models,which use low levels of ionizing radiation, and, the"millimeter wave" model, which use radio frequencies from 30GHz to 300 GHz (yeah, gigahertz. A gigahert is 1,000,000,000 cycles per second). The ionizing radiation of backscatter models is potentially carcinogenic to human tissue, and radiation doses are cumulativeto tissues that are repeatedly exposed. The radio frequencies of millimeter wave models are not currently considered to be inherently carcinogenic. However, there is much more information available about backscatter systems, which were introduced in 1992,than about the newer millimeter wave systems, which are still not widely used in airports.
For those of you who need a review, keep in mind that the DNA molecule, although very strong when all of the base pair “rungs of the ladder” are intact, they are connected only by hydrogen bonding, which is a weak molecular glue that can be trashed easily by chemicals and of course, totally demolished by radiation, resulting in mutations and cancer.
The debate over these scanning technologies in the news media has centered primarily on traveler privacy issues related to the images produced. The debate has focused only secondarily on the safety of the traveling public exposed to such scans and on the effectiveness of these technologies in detection.I believe issues of traveler privacy and machine effectiveness are best discussed in other venues or relative blogs. As a physician, I address concerns related to the safety of scanner radiation. Because the Department of Homeland Security views the body scanner issue to be a sensitive matter of national security, I anticipate that there is some information concerning these technologies that is not available to us.
When I teach radiology, one of the first things covered in class is the history of x-rays. After Wilhelm Roentgen discovered x-rays in 1895, it did not take long for this technology to reach medical use. By mid 1896, Dartmouth Medical School already had a working x-ray imaging device, however, what is not widely known, is that thousands of doctors, nurses, patients, and people in the waiting rooms died of radiation exposure over the next 30 years because of the novelty, lack of understanding of the danger, and of course, ignorance of health consequences and the need for shielding.
From the available literature reviewed, I found that radiation dosing from a single backscatter scan is reported as ranging from 0.005 millirem to 0.009 millirem (A rem is an abbreviation for “roentgen equivalent man”, which is a measure of ambient radiation exposure to a man in a particular environment). By comparison,a passenger on a cross-country flight receives approximately3 millirem of radiation, and the dose from a single chest radiograph is 10 millirem.
Backscatter systems have not proven to be harmful,according to several authorities, including the TSA, the US Food and Drug Administration's Center for Devices and Radiological Health, the National Institute of Standards and Technology,The Johns Hopkins University Applied Physics Laboratory, the Center for Radiological Research at Columbia University, the United Kingdom's Health Protection Agency, and the American College of Radiology. The American College of Radiology has reported that "a traveler would require more than 1,000 backscatter scans in a year to reach the effective dose equal to one standard chest x-ray."
There are 3 backscatter models that are currently manufactured for security screening. American Science and Engineering Inc of Billerica, Massachusetts, produces the SmartCheck; Rapiscan Systems of the United Kingdom produces the Secure 1000; andTek84 Engineering Group of San Diego, California, produces the Ait84. Of these devices, Rapiscan Systems' Secure 1000 is the most commonly used.
In an interview published in the Los Angeles Times in November 2010, Peter Kant, Rapiscan Systems' executive vice president of global government affairs, stated that his company produced 211 of the 385 image scanners then in use at the68 airports in which such machines had been deployed. (According to the TSA Web site, there were 486 image scanners at 78 airports as
of January 2011). Based on the previously cited report by the National Institute of Standards and Technology, it appears that Rapiscan Systems' Secure 1000 has been designed with appropriate safeguards for widespread deployment.
Despite the published reports that support the safety of backscatter technology, scientists at the University of California, San Francisco have recently raised questions about how radiation exposures were calculated in the reports—raising doubts about the accuracy of the dose-per-scan data.These scientific investigators have also raised questions regarding whether backscatter scanning would pose an added health risk for individuals who are genetically susceptible to particular cancers, for instance, those individuals with oncogenes such as the Philadelphia Chromosome.
These safety issues require further research. Moreover, I have been unable to find any reports of backscatter technologies being subjected to large-scale clinical outcomes studies or other medical testing with either human or animal subjects. Quite simply, we are in such a hurry to protect ourselves, we are not protecting ourselves from ourselves.
As previously noted, questions regarding the effectiveness of scanner technologies are best left to other venues. Nevertheless,all medical decisions involve considerations of risk vs benefit.If a procedure carries a potential risk (such as radiation exposure)and if the procedure's benefits are in question, such facts would be important to know in making medical decisions, including the decision on whether an individual agrees to be scanned.
In April 2010, The Vancouver Sun published a revealing interview with Rafi Sela, former chief security officer at the Israel Airport Authority and a 30-year veteran in airport security and defense technology who helped design security measures at Ben Gurion International Airport in Tel Aviv. Mr Sela was quoted as saying,"I don't know why everybody is running to buy these expensive and useless ‘full-body scanner machines’. I can overcome the body scanners with enough explosives to bring down a Boeing747.... That's why we haven't put them in our airport."
In regard to millimeter wave technology, Ben Wallace, a member of the British Parliament who worked on millimeter wave scanners for the defense research organization QinetiQ, was quoted as saying, "The millimeter wave technology is harmless, quick and can be deployed overtly or covertly. But it cannot detect chemicals or light plastics." This limitation could prove to be a serious obstacle in the widespread adoption of millimeter wave technology in airport security.
Of course, the adoption by terrorists of alternative strategies designed to bypass both backscatter and millimeter wave machines, such as bodypacking, could render both types of scanners irrelevant.Although concerns about the effectiveness of these devices may one day make the issue of safety mute, such questions persist today.
In summary, given the current state of scientific knowledge, backscatter radiation scans maybe safe, with appropriate built-in safeguards to allow these machines to be deployed for everyday use by appropriately trained personnel. However, large-scale clinical testing of these devices has not yet been performed, and there are legitimate questions concerning the effectiveness of these machines in accomplishing the task for which they were designed.
Therefore, using the logic of the risk-benefit ratio, it might be prudent to obtain more information on clinical exposure and more confirmation of device effectiveness before exposing large segments of the population to these full-body scanners and the radiation they produce.