January 13, 2011 — Air travel has not been the same since September 11, 2001, when 4 commercial airplanes were hijacked and transformed into lethal weapons. Air passengers have since become accustomed to increased security, but the latest attempt to detect would-be terrorists has been mired in controversy.
The Transportation Security Administration (TSA) has begun to ramp up the deployment of whole-body backscatter scanners at security checkpoints in airports across the United States. These scanners deliver narrow, low-density x-ray beams over the entire person, front and back. The radiation is delivered at high speed and reflects off the body and presumably on objects that may be hidden on the person; the aim is to detect any hidden weapons or explosive devices.
|A volunteer goes through a full body scanner at O'Hare International Airport, in Chicago, Illinois. AP Photo|
However, despite assurances from the TSA and the US Food and Drug Administration (FDA) that the technology is safe, a number of radiation experts have voiced concerns about the widespread use of these scanners.
Concerns have been raised about the lack of independent safety data and a possible heightened risk in several specific populations. These include older travelers, immunocompromised individuals, including HIV and cancer patients, and children and pregnant women.
But the main concern is whether these new scanners increase an individual's risk of developing cancer.
Unfortunately, the answer to that question depends on who is being asked. Both the TSA and the FDA say that the technology is unequivocally safe for all passengers and that the radiation dose is too low to cause any health risk. Some professional organizations, such as the American College of Radiology, agree with that summation. Other medical groups, such as the American Academy of Dermatologists, have not yet issued a position on the subject, despite concerns that there might be an elevated risk for skin cancer.
Potential Serious Health Threats
Four experts in imaging and oncology from the University of California, San Francisco (UCSF) have voiced "concerns about the potential serious health risks of the recently adopted whole-body backscatter x-ray airport security scanners." They outlined their concerns in a letter, sent in April 2010, to President Obama's science and technology advisor, John Holdren, PhD.
Our overriding concern is the extent to which the safety of this scanning device has been adequately demonstrated.
"Our overriding concern is the extent to which the safety of this scanning device has been adequately demonstrated," they wrote. "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 of the available relevant data [are] reviewed."
The authors noted that their colleagues at UCSF, along with dermatologists and cancer experts, are particularly concerned about widespread exposure to specific populations. Immunocompromised individuals are likely to be at risk for cancer induction by the high dose to the skin, they pointed out. Also at risk is the large population of travelers older than 65 years, who face a particular risk from the mutagenic effects of x-rays related to the known biology of melanocyte aging.
In addition, there is a risk for sperm mutagenesis because of the proximity of the testicles to skin. And the risk for radiation emission to children and adolescents does not appear to have been fully evaluated, the letter authors noted.
In closing, they urged that an impartial panel of experts be allowed to reevaluate the "potential health issues we have raised before there are irrevocable long-term consequences to the health of our country. These negative effects may on balance far outweigh the potential benefit of increased detection of terrorists."
Six months after the letter was sent, the FDA and TSA issued a joint response, addressing the concerns that were raised, and reiterating their position that "the potential health risks from a full-body screening with a general-use x-ray security system are miniscule."
They noted that the technology has been available for nearly 2 decades and that their evaluation was based on scientific evidence and on the recommendations of recognized experts. In addition, they pointed out that there are "numerous publications regarding the biological effects of radiation and the appropriate protection limits for the general public that apply to these products."
We are confident that full-body x-ray security products and practices do not pose a significant risk to the public health.
"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," concludes their response.
However, the UCSF experts remain unconvinced. "We are writing a careful response to the flawed FDA/TSA answer to our letter," coauthor John Sedat, PhD, told Medscape Medical News.
In the meantime, Dr. Sedat, professor of biochemistry and biophysics at UCSF, plans to avoid the scanners. "All I can say is that I, at age 68, also have precancer skin problems, and will not go through these machines or be groped," he said. "I just will not travel by plane. Sadly, I can't travel in my own country."
For travelers who want to avoid the scanners, the TSA offers an "enhanced pat down," which has produced as much controversy as the x-rays. The pat down is more intrusive than it was previously; instead of using the "palms up" method, screeners are now using the "hands on" method.
There has been a flurry of reports that some TSA agents have been "overenthusiastic," with many passengers complaining that the touching goes too far. The procedure has also resulted in embarrassment and humiliation for some passengers. Incidents have included patting that resulted in a broken seal on a urostomy bag worn by a bladder cancer survivor, leaving the passenger covered in urine, and the request that a breast cancer patient remove her breast prosthesis.
Thus, for some travelers, such as Dr. Sedat, the screening options are equally unpalatable.
Scanners Are Safe
To quell concerns about the safety of scanners, the FDA has created a Web page dedicated to providing information to the public about body scanners. In a statement, Daniel Kassiday, an engineer at the FDA, pointed out that the "dose from 1 screening with a general-use x-ray security screening system is so low that it presents an extremely small risk to any individual."
A person receives more radiation from naturally occurring sources . . . than from 1 screening.
"A person receives more radiation from naturally occurring sources in less than an hour of ordinary living than from 1 screening with any general-use x-ray security system," he explained.
Mahadevappa Mahesh, MS, PhD, associate professor of radiology and medicine at Johns Hopkins University School of Medicine in Baltimore, Maryland, agrees. "The radiation dose from a single backscatter system is very low," he said in an interview. "A single backscatter scan is equivalent to about 30 minutes of natural background radiation or about 4 to 5 minutes of air travel."
"A person would need to undergo 1000 to 2000 backscatter scans to receive the radiation dose equivalent to a single medical chest x-ray dose," he added.
Dr. Mahesh pointed out that along with other regulatory agencies, the Nuclear Regulatory Commission recommends an annual limit to the public of 1000 microsieverts (μSv) of radiation from all sources. In addition, it recommends an annual limit of 250 μSv from any single source. The dose from backscatter scans might be as low as 0.05 μSv.
Thus, at a range of 0.05 to 0.10 μSv, the 250 limit would be reached only if a person undergoes 2500 to 5000 scans per year. That is highly improbable for any traveler, Dr. Mahesh noted.
Dr. Mahesh also does not believe that there is an increased risk for skin cancer, which was one of the points raised by the UCSF experts in their letter to the White House. "The actual time of the beam on the person's skin surface is a fraction of a second, because the entire scanning pattern is completed in 8 to 15 seconds," he said. "The letter introduced unnecessary fear to the general public."
Current calculations indicate that backscatter scans are safe for the public at large, even infants and children, pregnant woman, and those with genetically based hypersensitivity to radiation, he said.
Dr. Mahesh emphasized that in medical imaging, radiation delivery systems must be tested and the radiation dose verified after any maintenance or upgrade. "The same is true for these systems," he said. It is essential to establish routine maintenance and quality-assurance programs that involve trained professionals to verify the radiation dose delivered by the backscatter systems, he added.
Individual vs Population Risk
Radiation expert David J. Brenner, PhD, DSc, feels that the backscatter scanners are not inherently dangerous, but in the same vein, might not be as safe as the FDA and TSA assert.
Trying to estimate the risks associated with these very low radiation doses involves a lot of uncertainty.
"Trying to estimate the risks associated with these very low radiation doses involves a lot of uncertainty," said Dr. Brenner, Higgins Professor of Radiation Oncology and director of the Center for Radiological Research, Columbia University Medical Center, New York City. "In my view, one needs to distinguish between the individual risk from going through the scanner once, the risk for a very frequent flier or a pilot who might go through security 200 or 300 times each year, and the overall risk to the entire community of air travelers going through these scanners."
On an individual level, going through a scanner once carries a risk that is miniscule, Dr. Brenner told Medscape Medical News. When that "miniscule risk" is multiplied 200 or 300 times, the estimated individual risks are still small, but perhaps can no longer be described as "miniscule."
The bigger concern, contends Dr. Brenner, is the overall population risk. As an example, if 10 people are exposed to that small of a risk, the chances are that none of them will develop cancer related to scanner exposure.
But that changes with a larger number of people. "If a billion people are each exposed to a risk of 1 in 10 million, then chances are that some of them will get cancer as a result of that activity, even though the individual risk is extremely small," he explained. "So even though the individual risk is very small, the impact on the population may not be small if the exposed population is large. This is potentially the case with airport x-ray scanners."
When the scanners were being used for only a small fraction of all fliers, there were few concerns about safety issues, Dr. Brenner noted. But the TSA policy has changed, and now the goal is to have all air travelers pass through these devices.
Dr. Brenner pointed out that another type of full-body scanners, known as millimeter wave scanners, do not use x-rays and have no associated safety issues. The TSA is also deploying them, but in fewer numbers than the other type. "From the overall public health point of view, if millimeter wave scanners are just as sensitive for detecting concealed explosives, there is a good argument that they should be being deployed in airports rather than the x-ray scanners," he said.
To further fan the flames of controversy, an investigative report has suggested that there are discrepancies in the TSA's claims. According to AOL News, the TSA says that a number of groups, including the FDA, the US Army Public Health Command, Johns Hopkins Applied Physics Laboratory (APL), and the Health Physics Society, are all involved in determining and ensuring the safety of these systems. However, all of these groups deny that they have any responsibility for the ongoing safety of the scanners.
Specifically, AOL News contends that the TSA reports that the Army is involved in its safety program and that experts from the US Army Public Health Command routinely check 464 scanners that are located in 75 American airports. In reality, the TSA only requested that the Army check 15 scanners in 3 airports. Although no problems were found, the Army experts reported that none of the machines examined had the required warning label that states: "Caution: X-Rays Produced When Energized."
The TSA also often refers to a safety study that it commissioned, and that was conducted by the Johns Hopkins APL. But the assertion that it has helped to ensure public safety is misleading, according to AOL News.
The role of APL was to measure radiation coming off the body scanners to verify that it fell within acceptable standards, according to Helen Worth, head of public affairs for the Johns Hopkins lab.
She told AOL News that they were "testing equipment and in no way determined its safety to humans." Even though a number of media stories have stated that APL found the equipment to be safe, "that was not what we were tasked to do," said Ms. Worth.
AOL News also notes that the FDA does not conduct routine inspections of any nonmedical x-ray unit. They have not field-tested the scanners or performed any inspection of the manufacturer. The FDA told AOL News that they do not have the legal authority to require the owners of these devices, including the TSA, to provide access for routine testing once they have been sold.
Finally, the Health Physics Society has endorsed the use of the scanners for security screening, but only if there is compliance with nationally accepted exposure standards. But the organization informed AOL News that they do not monitor the safety of the scanners. The TSA has refused requests by the Health Physics Society for data that they collect on radiation exposure in and around its full-body scanners.
Into the Fray
In fact, the TSA has not released any exposure data for independent analysis, or inspection reports. This lack of disclosure has caught the attention of some members of Congress, who have now entered the fray and are calling on the TSA to release this information.
Last year Congressman Rush Holt (D-NJ) wrote to TSA Administrator Frank Pistole, expressing his concerns about the new screening procedures and urging the TSA to consider health and privacy implications.
Rep. Holt, who is a physicist and former chair of the House Select Intelligence Oversight Panel, questioned the ability of scanners to deter terrorists. He cited research that indicates that most of the radiation from x-ray backscatter machines strikes the top of the head, which is where 85% of basal cell carcinomas occur.
Congressman Edward Markey (D-Mass), a senior member of the Energy and Commerce Committee, has sent letters to Department of Homeland Security Inspector General Richard Skinner and Mr. Pistole requesting information on how the TSA ensures the adequacy of its efforts to maintain and evaluate these scanning systems.
He has requested a report from Inspector Skinner that addresses the following issues:
The effectiveness and reliability of TSA inspection plans for catching and resolving any potential issues that could arise with the functioning of the general-use full-body x-ray screening systems.
The efficiency of TSA quality-control plans to ensure that the systems and protocols being used remain in compliance with the general-use dose-per-screening limit of 0.25 μSv.
The manner in which TSA employees are trained in the appropriate operation and troubleshooting of the machines.
The way in which information about accidental overdoses is shared with other federal agencies and irradiated passengers or employees.
The coordination with other federal agencies, including the FDA, that have more subject matter expertise in this area.
In addition, Rep. Markey has asked Mr. Pistole to furnish documentation and provide responses to the following questions:
How often does the TSA plan to inspect the full-body x-ray screening systems to ensure that the radiation emitted is within acceptable standards?
What does this inspection entail and who is responsible for performing these inspections?
What are the maintenance and enforcement strategies that the TSA has in place to ensure that all screening systems and protocols being used remain in compliance with the general-use dose-per-screening limit?
What policies does the TSA have to ensure that any inappropriate dosage that occurs as a result from either human error or malfunctioning of the equipment is promptly reported to the individual(s) who are likely to have received a higher dose, and that the machines are repaired?
Does the TSA have dosimeter monitoring plans in place for TSA employees?
Surely it is possible to secure an airplane without sacrificing individual liberties or privacy.
Congressman Jason Chaffetz (R-Utah) agrees that more oversight is needed, not only for possible safety concerns, but for privacy issues as well. In a recent letter to President Obama, he stated that "surely it is possible to secure an airplane without sacrificing individual liberties or privacy. We can utilize bomb-sniffing dogs, [advanced imaging technology] machines as a method of secondary screening, and behavioral profiling to accomplish the shared goal of safe and secure air travel."
Rep. Chaffetz previously cosponsored legislation that would limit the use of the full-body scanners. The amendment to the Transportation Security Administration Authorization Act, H.R.2200, opposed the use of full-body scanners as a primary screening tool at airports, and allowed passengers to opt for a pat-down search instead. The bill passed the House but stalled in the Senate.
Now, as the new chair of the House Oversight Subcommittee on National Security, Homeland Defense and Foreign Operations, which oversees the TSA, Rep. Chaffetz intends to reintroduce a bill that is similar to the one that failed to pass.
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Cite this: Are Full-Body Airport Scanners Safe? - Medscape - Jan 13, 2011.