By Calvin Biesecker

The health risks to individuals screened by X-ray-based imaging systems that are being used to screen people for concealed threats in some airports in the United States and internationally are “miniscule,” according to a joint letter from Food and Drug Administration (FDA) and Transportation Security Administration (TSA) officials who responded to a request from the White House science adviser to describe the safety of the machines.

“There are numerous publications regarding the biological effects of radiation and the appropriate protection limits for the general public that apply to these products,” John McCrohan, deputy director for Technical and Radiological Initiatives at the FDA, and Karen Shelton Waters, TSA’s Chief Administrative Officer, say in their Oct. 12 letter to John Holdren, director of the White House Office of Science and Technology Policy (OSTP). “As a result of these evidence-based, responsible actions, we are confident that full-body X- Ray security products and practices do not pose a significant risk to the public health.”

The letter from the FDA and TSA was released this week on the OSTP web site.

Holdren’s request was prompted by a letter sent to him last April from some faculty at the Univ. of California-San Francisco (UCSF) concerned about the “potential serious health risks” associated with the use of backscatter X-ray Advanced Imaging Technology (AIT) being deployed by TSA. The AIT systems in question are made by OSI Systems [OSIS] Rapiscan division. TSA is also buying AIT systems from L-3 Communications [LLL] that are based on active millimeter wave technology that has not elicited similar health concerns as the X-ray-based machines.

In their April 6 letter to Holdren, the UCSF professors said their “overriding concern is the extent to which the safety of this scanning device has been adequately demonstrated. This can only be determined by a meeting of an impartial panel of experts that would include medical physicists and radiation biologists at which all relevant data is reviewed.”

And in their detailed, reply, the FDA and TSA officials say that regulation of AIT systems goes back 20 years and that in 2002 the first consensus-based national standard was created regarding the upper limit of radiation a person should be exposed to in a year. That level is 25 millirems, which means a person would have to be screened more than 1,000 times to reach this annual limit, they say.

The national standard was further revised and published in late 2009, taking account of a number of new system designs that have been developed to screen people with X-ray technology, although the annual effective dose limit of 25 millirems was retained.

The FDA and TSA officials point out that TSA requires that manufacturers of full-body X-ray screening equipment adhered to the standard. Moreover, countering the UCSF letter claiming that independent safety results don’t exist, the federal officials cite five examples of independent measurements conducted between 1991 and 2009 on various versions of Rapiscan’s Secure 1000 system, saying “all results are consistent with the dose specified by the manufacturer.”

On its web site, UCSF says it has received Holdren’s reply to their April letter and is reviewing its details in consideration of “the appropriate next step to advance the issue.”

TSA delayed for years the operational deployment of AIT systems due to privacy concerns that the machines reveal too much bodily detail of a person. To address these issues, the technology was improved somewhat to blur certain features such as a person’s face and other measures were taken such as locating the TSA officer reviewing the images remotely from where the actual screening occurs and disabling the ability to store and print images.

As for the health concerns, TSA has long maintained that the AIT units are safe. On its web site, the agency says that a single scan by a backscatter X-ray system produces is the equivalent radiation of two minutes of flying on an airplane while the millimeter wave-based system produces energy that is “thousands of times less than a cell phone transmission.”

Regardless of TSA’s attempts to ease people’s concerns about the health effects of the body scanners, the union representing US Airways [LCC] pilots this month urged its members to avoid using the machines and instead submit to a private pat down search that is observed by a fellow crew member.