In a recent article entitled Radiation risks: Are airport body scanners ‘a great public health experiment’?”, Leon Kaufman argues that the use of these scanners at airports exposes airline passengers to undetermined amounts of radiation without reason and with little knowledge of the consequences.
I would like to address certain incorrect assertions in this article. Whole Body Imagers manufactured by American Science and Engineering (AS&E) rigorously adhere to the standard that is designed to govern x-ray scanners for security applications, the American National Standards Institute (ANSI) standard 43.17. This standard was written with input from a wide variety of industrial, military, National Laboratory, and government experts, including representatives from the National Institute of Standards and Technology (NIST), the Department of Homeland Security (DHS), the Occupational Safety and Health Administration (OSHA), and the Center for Devices and Radiological Health (CDRH), a section of the U.S. Food and Drug Administration (FDA) responsible for regulation of radiation producing equipment.
While surely there are misunderstandings as to how x-ray backscatter personnel scanners function, it is true that these scanners utilize ionizing radiation, and that the x-rays emitted from them penetrate skin, as well as clothing. However, it is the dose, truly negligible by any standard radiation metric, which is of importance here.
For more on this topic: Radiation risks: Are airport body x-ray scanners ‘a great public health experiment?’ A traveler’s guide to digital imaging Whole-body airport scanners are basically safe—or are they? British Medical Journal editorial defends whole-body airport scanners |
First, let me note that my comments refer specifically to x-ray backscatter systems that are designed to scan people, such as AS&E’s SmartCheck personnel screening system. In order to perform a backscatter scan, a well-collimated beam of x-rays is sequentially scanned, at a very high rate in a horizontal direction across a person’s body, while simultaneously moving down at a lower rate of speed. The entire scan takes a few seconds. The dwell time of the relatively small-diameter beam at each point of the person’s body is extremely short (measurable in microseconds), in contrast to medical x-rays, for example, that may irradiate a much larger area on a person for 1000 times as long, or longer. The x-ray dose delivered by the SmartCheck system is measured according to well-established guidelines using calibrated ionization chambers and following the procedures described in ANSI Standard N43.17, Annex C. The doses that we measure, and that have been confirmed by a number of independent measurements, are less than 10 microrem per scan (or equivalently, less than 0.1 microSievert per scan), using this well-established ANSI procedure. This dose falls into the category described as “trivial” by radiation experts from the Health Physics Society.
According to the published ANSI standard for general-use systems, at this dose level an individual could be scanned 2500 times per year with SmartCheck before reaching the annual limit suggested for security screening by the U.S. National Council on Radiation Protection and Measurements (NCRP 2003) of 250 µSv, which is a quarter of NCRP’s recommended dose limit from all radiation sources for the general public. The NCRP’s all-source limit is the same as that of the International Commission on Radiological Protection (ICRP 2007), the U.S. Nuclear Regulatory Commission (10 CFR 20), and the U.S. Department of Energy (10 CFR 835).
It is important to keep in mind that all of us are exposed to ionizing radiation every day of our lives, from many parts of our environment, including the food we eat, the building materials used in our homes, and even the altitude of the cities and towns in which we live. The radiation dose received from a backscatter scanner should be looked at in this context.
The effective dose from a scan by the SmartCheck system is equivalent to:
- About 1% of the radiation dose received by the average person on any day of the year, much of which is from natural sources.
- Less than 0.2% of the radiation received from a medical chest x-ray.
- The radiation dose received from flying two minutes in an airplane at 30,000 feet (due to the increased exposure from cosmic rays.). A flight from Boston to Los Angeles, for example, exposes a passenger to the equivalent of 180 SmartCheck scans, still trivial, and due to the increased exposure to cosmic rays at higher altitudes./
In this context, we believe one gets a much better sense of how truly minute the radiation dose is from a backscatter scanner.
One may ask: Why is any dose justified at all? From a radiation protection standpoint, no exposure is justified unless it produces a net positive benefit. In the case of security screening, it is becoming increasingly apparent (from security breaches similar to what occurred in the recent “underwear bomber” case) that many organizations charged with maintaining security are coming to the conclusion that techniques such as x-ray scanning of passengers are an effective means of preventing events that could lead to tragic consequences for large numbers of people. This is because SmartCheck enhances the security inspection process by displaying threats concealed under a person’s clothing, including many items that a metal detector would miss.
I would argue that the risks associated with the dose delivered by backscatter security screening are certainly trivial both compared to typical daily exposures from natural sources, and also compared to the benefits to the traveling public from dramatically improved security. More importantly, those in charge of our nation’s security are coming to the same conclusion, and increasingly, their counterparts in other nations are as well.
Finally, Dr. Kaufman asserts that AS&E’s BodySearch system “permits hard-copy printing and storage of images.” In fact, this particular product he references is no longer manufactured by AS&E. In 2005, AS&E introduced the SmartCheck personnel screening system. The privacy-enhanced SmartCheck system is not capable of storing, exporting, or printing images.
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In sharp contrast to the image shown in the article, the SmartCheck system’s privacy image provides only an outline of the individual that looks more like a chalk drawing than a real person, with information to help identify the nature and location of any threats. The easy-to-understand image also eliminates the need for intrusive pat-down searches. In fact, in pilot tests conducted by TSA at multiple U.S. airports, over 90% of passengers chose a SmartCheck scan over a pat-down search.
We trust that, when presented with these facts, people will recognize the value of this technology, and how beneficial it can be in improving security, not only for airline passengers, but in other venues as well.
References
ANSI/HPS N43.17-2009 American National Standard: Radiation safety for personnel security screening systems using x-ray or gamma radiation. Approved: August 2009.
Health Physics Society. Position statement of the Health Physics Society: Use of ionizing radiation for security screening of individuals: PS017-1. December 2009.
Strom D. Screening individuals with backscatter x-ray systems. McLean, VA: Health Physics Society, 2005.
National Council on Radiation Protection and Measurements (NCRP). Screening of humans for security purposes using ionizing radiation scanning systems. Bethesda, MD: NCRP Commentary No. 16, National Council on Radiation Protection and Measurements, 2003.
International Commission on Radiological Protection. “The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication No. 103.” Ann ICRP 37(2-4), 2007.
National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. NCRP Report No. 160. Bethesda, MD: NCRP Publications, 2009.
U.S. Nuclear Regulatory Commission. Standards for protection against radiation. 10 CFR 20. Title 10, Code of Federal Regulations, Part 20. Washington, DC: U.S. Government Printing Office, 2010.
U.S. Department of Energy. 2010. Occupational Radiation Protection. 10 CFR 835. Title 10 Code of Federal Regulations, Part 835. Washington, DC: U.S. Government Printing Office, 2010.
