Airport security scans and fertility

December 1, 2010Carole No Comments »

It’s the holiday travel season and the new full body scans used for airport security are on everyone’s mind. Aside from issues about civil liberties, are these scans safe? On the internet, you will easily find hysteria based on bad facts, unfounded fears and conspiracy theorists who believe that our government is trying to kill us with the new scans. You can also find some non-inflammatory debate between government officials, scientists and private citizens regarding the health effects of the new technology.

A group of scientists at the University of California San Francisco recently voiced their concerns regarding the new technology. In an open letter to Dr. John P. Holdren, Assistant to the President for Science and Technology. The UCSF scientists are primarily concerned about the concentration of radiation at the level of the skin and just below and feel that adequate research has not been done before implementation.They identify specific populations and tissues which they believe may be most at risk.

A.) Older travelers, >65 years of age, at greater risk of skin damage due to ageing of melanocytes which protect the skin.
B) Women who have a known increased risk of breast cancer due to existing
defects in DNA repair mechanisms. This group is usually advised to avoid X-ray mammograms.
C) White blood cells just under the skin would also be at increased risk for mutagenesis.
D) Immunocompromised individuals–HIV and cancer patients
E) Pregnant women, children and adolescents may have risks that have not been fully evaluated.
F) Testicles with sperm producing cells are just below the scrotal skin and may have increased risk for
sperm mutagenesis.
G) Risks to cornea and thymus may not be known.

The UCSF scientists also raised concerns about the resources available to airports for ensuring that scanners are properly operated and calibrated after a hardware repair or software update.

Dr. Holdren shared the scientist’s letter of concern with John L. McCrohan who is the Deputy Director for Technical and Radiological Initiatives at the Food and Drug Administration. Mr. McCrohan and Karen R. Shelton Waters, Deputy Assistant Administrator /Chief Administrative Officer, Designated Safety and Health Official at the Transportation Security Administration. McCrohan and Waters prepared a public response to the “red flag” concerns raised by the UCSF scientists.

The FDA did perform an evaluation of safety risks from security scans. The FDA sponsored a working group composed of industry experts and scientists to identify a safe dose for scanners. The group published  “Radiation Safety for Personnel Security Screening Systems Using X-rays1” which established a standard that no scanned person should receive “an effective dose in excess of 0.25 mSv (25 mrem) in any 12-month period.” According to the response letter, vulnerable populations were considered when this maximal dose level was determined.

Because newer scanners were developed since the 2002 report, the FDA re-evaluated the allowable safe dose in 2009 and published a revised standard , “Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiation, which “retained the annual effective dose limit for members of the public of 0.25 mSv (25 mrem). This standard defines a general-use x-ray screening system  as one that delivers less than 1/1000 of this dose per screening (0.25 µSv (25 µrem).” The TSA requires that any scanners used at airports deliver less than 1/1000 of the annual allowable dose.

The “general use system” referred to in the report is the same as the “backscatter” systems mentioned in the popular press. The term back scatter comes from the way the system creates an image by using small amounts of x-ray energy  that “bounces” off the person being screened. The x-rays bounced back from the person are detected by sensitive detectors and analyzed by a computer to produce the controversial “naked” image.

The response letter goes on to say that the annual recommended limit for skin exposure to the general public is 50,000 µSv. According to the letter, “The dose to the skin from one screening would be approximately 0.56 µSv when the effective dose for that same screening would be 0.25 µSv. Therefore the dose to skin for the example screening is at least 89,000 times lower than the annual limit.”

The UCSF letter raised concerns about the possible concentration of radiation at the skin level, resulting in higher effective doses than if the radiation was equally distributed throughout the entire volume of the body. Effective doses are usually based on whole body exposure. The FDA response is that at most, skin exposure would be three times the effective dose and over 1000 scans would be needed to approach an annual limit of exposure.

Regarding the safety of the hardware or software, the response letter points to FDA requirements that manufacturers have safety systems in place and immediately inform the FDA about any changes in their system design or performance. Also, the FDA requires manufacturers report any adverse safety events. These requirements are not particularly reassuring since the FDA appears to be overwhelmed with its existing responsibilities. The letter concludes, “In summary, the potential health risks from a full-body screening with a general-use x-ray security system are miniscule.” At the bottom of the letter, you can find a list of resources and studies used to come to these conclusions if you are interested.

The American College of Radiology, the professional society for radiologists, radiation oncologists, medical physicists, interventional radiologists and nuclear medicine physicians also issued a reassuring statement regarding safety.

Other issues, such as image pixel size also impact the effective dose that a person might receive and this issue was not discussed in the response. Can scan operators adjust the pixel size and thus the dose? What is the upper limit of exposure?

Interestingly, according to the FDA, everyday living and actually flying in the airplane provide you with more exposure to ionizing radiation than one airport scan. Consider this, every 42 minutes of actual living exposes you to the equivalent of one airport scan because naturally occurring ionizing radiation is all around us. Two minutes of flight time is equivalent to the dose from one airport scan.

Are the UCSF scientists satisfied? No, according to this CNN report which has a nice summary of the issues. Dr. Marc Shuman, a cancer researcher and his colleagues are writing a rebuttal to the Department of Health and Human Services letter, calling the agency’s arguments “seriously flawed.” They would like to see a moratorium on full-body scanning until further study is conducted.

How about reproductive safety? As far as I could tell from the existing research referenced in the FDA report, no specific fertility studies were cited. The dearth of fertility studies is hardly surprising since you couldn’t ethically use human subjects and animal studies are frequently criticized as not being relevant. Robert Brent, MD, PhD of the Health Physics Society published a summary of radiation exposure during pregnancy.

The Health Physics Society report states that to cause a miscarriage, exposures above 200 mSv are usually necessary. Most diagnostic procedures deliver less than 50 mSv, according to Dr. Brent. A airport scan delivers less than 0.25 µSv. Remember in the metric system, one thousand micro (µ) units equal one milli (m) unit. So an airport scan is tens of thousands of units less than needed to induce a miscarriage. Developmental abnormalities are another concern and can be induced by radiation exposure in later weeks of pregnancy (after the first two weeks) if exposures over 200-300 mSv occur.

The Health Physics society has issued its own policy statement about the “Use of Ionizing Radiation for Security Screening Individuals” which you can read here. Briefly, the society states that:

  1. The practice of using radiation to scan people should be limited to those applications that result in an overall net benefit to society.
  2. When the practice is used to screen members of the general public, the effective dose delivered should not exceed 0.25 µSv (25 microrem) per screening, or  250 µSv (25 millirem) in a year. (Doses achieved with about 1000 scans)
  3. Subjects should be informed of the radiation exposure.

The John Hopkins Applied Physics Laboratory performed an engineering study for the TSA to measure exposures from radiation produced by the RapiScan brand of security scanner. Exposures were determined from radiation detected by sensors- no humans were harmed in this study! The heavily redacted study report can be accessed from the TSA site. I am not an engineer so I can’t evaluate the report, but the conclusion of the report is that the delivered dose from the scan would be less than the maximum allowed 0.25 microSv, if the scanner is functioning correctly.

I think questions still remain about the use and maintenance of these instruments. I don’t know how confident we should be that dose limits can not be exceeded by either operator error or equipment malfunction. That doesn’t mean that we are actually at risk, just that it is difficult to find reassurance in the public domain regarding operational concerns.

I don’t believe our government is trying to kill us. Who would be left to pay the taxes? I do think that life is full of risks and we must make choices based on ongoing risk/benefit analysis. We could eliminate all security screening, totally preserve our civil liberties and probably increase our security risks. Taking my chances actually appeals to the libertarian streak in me but no one is putting that option on the table. So, for the foreseeable future, we must choose between being scanned or groped. Neither option is particularly palatable. The scans are probably safe enough if you fly less than 1000 times a year.  If you need a 100% guarantee of safety, no one can guarantee that, but you might have more peace of mind opting out of the scan.

© 2010, Carole. All rights reserved.

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