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Turning to Your Health now, today we'll look at the dangers of radiation at airport security checkpoints. Few people think twice about passing through airport scanners, but concerns are being raised about the small dose of x-rays that some new airport machines are putting out.

NPR's Richard Knox assesses the risk.

RICHARD KNOX: At a time when terrorists board airplanes with bombs in their underwear, we're all pretty tolerant of the airport security drill.

Unidentified Woman: Sir, do you have anything in your pockets?

Unidentified Man: No.

Unidentified Woman: Please remove your boarding pass and hold that in your hand. Are you wearing a watch?

KNOX: Boston, where I live, has one of the first airports to get the very latest in security technology. At the checkpoint, TSA workers are asking people to take off their shoes and belts and empty their pockets. Nothing new about that. But then passengers are asked to walk between two big blue boxes.

Unidentified Woman: You'll be walking through the new body scanners.

KNOX: Plant their feet on two squares and raise their arms in the air. While they're holding still for about six seconds, a narrow beam of low-energy X-rays scans them from head to toe. In a separate room, a screener eyeballs the images for concealed weapons or explosives. For privacy, the scans look like sketches made with chalk.

Most people seem to be taking it in stride, like Jason Snipes, who's on his way to North Carolina.

Mr. JASON SNIPES: My wife's pregnant. You know, you're not supposed to be around X-rays. But, like, for me, personally, no, I don't have any concerns or anything like that. And if it helps, I'm all for it.

KNOX: Magdi Hannah(ph) is headed home to San Diego. He got X-rayed coming and going.

Mr. MAGDI HANNAH: It was a pretty normal thing. I didn't feel like anything made a difference.

KNOX: Most others I saw wore the "whatever" expressions of experienced travelers, and that's striking since we're all indoctrinated with the idea that radiation is a dangerous thing.

Dr. DAVID AGARD (University of California at San Francisco): Many people will approach this as, oh, it must be safe. The government has thought about this, and I'll just submit to it.

KNOX: That's David Agard of the University of California at San Francisco.

Dr. AGARD: But there really is no threshold of low dose being OK. Any dose of X-rays produces some potential risk.

KNOX: Agard's a biochemist and a biophysicist. He and several of his colleagues at UCSF recently wrote a letter to President Obama's science advisor, asking for a more thorough look at the risks of exposing all those airline passengers to X-rays.

Dr. AGARD: Ionizing radiation such as the X-rays used in not only these scanners, but also in medical X-rays, really have the potential to induce chromosome damage, and that can lead to cancer.

KNOX: The San Francisco group thinks the machine's manufacturer and government officials have miscalculated the dose that the X-ray scanners deliver to the skin. That's where nearly all the radiation is concentrated.

The manufacturer, Rapiscan, declines to comment. Federal officials have prepared a formal reply. They defend their calculation and insist the radiation dose from the scanners is below negligible.

The UCSF scientists aren't the only ones with concerns, though. David Brenner heads Columbia University's Center for Radiological Research. He recently´┐Żbriefed congressmen and staffers on the new airport scanners.

Dr. DAVID BRENNER (Center for Radiological Research, Columbia University): There really is no other technology around where anyone has been planning to X-ray such an enormously large number of people.

KNOX: Brenner thinks the risk to most individual travelers is miniscule. But he worries about the unknowns of scanning something like 700 million travelers a year. Brenner says recent research indicates that about one person in 20 is especially sensitive to radiation. They have gene mutations that make them less able to repair X-ray damage.

Dr. BRENNER: I don't know if I'm one of those 5 percent. I don't know if you're one of those 5 percent. And we don't really have a quick and easy test to find those individuals.

KNOX: All children are also more vulnerable to radiation damage, which can lead to cancer years later. Brenner says the most likely risk is a common type of skin cancer called basal cell carcinoma, which is usually curable. It often occurs on the head and neck. He points out that it'd be pretty hard to conceal a weapon or explosive on your head or neck. So, to him, that suggests a work around - avoid scanning the head and neck.

But TSA officials say that's not practical. Think of the long lines, they say, if the machines had to be readjusted for the height of every passenger. In any case, the TSA's Maurine Fanguy says the health risk is so tiny that it's not necessary to avoid the head or neck or to exempt children.

Ms. MAURINE FANGUY (Office of Security Technology, TSA): It is optional, and so parents can choose for children not to undergo screening. Personally, as a mother of two young children, I want to ensure that all technology that we use is safe. And we would not deploy technology unless we had done very rigorous and thorough health and safety testing.

KNOX: Over at the FDA, officials are equally confident. Daniel Kassiday is a specialist there in radiation hazards. He says the amount of radiation from an airport scanner is nothing to worry about. It's far below what airline passengers get from cosmic rays at 30,000 feet.

Mr. DANIEL KASSIDAY (FDA): At worst case, flying from New York to L.A., assuming a five-hour flight, it would take 75 screenings to equal the dose you get from that one flight. Or, more simply, one screening is equivalent of four minutes in the air.

KNOX: Kassiday also dismisses scientists' concerns that the scanners could malfunction and give passengers too high a dose.

Mr. KASSIDAY: Are they going to break? Possibly, you know, eventually. Am I really worried there's going to be a significant dose as a result? Not really.

KNOX: Brenner, the Columbia University radiation expert, says there's an obvious answer to all these questions.

Dr. BRENNER: Put more interest in the millimeter wave scanners, which, as far as we know, don't have any radiation risks associated with them.

KNOX: Millimeter wave scanners: That's a different kind of machine that produces comparable images using radio waves, not X-rays.

The TSA plans to deploy roughly equal numbers of the X-ray and millimeter wave machines. So I ask officials why they don't just use millimeter wave. They say they don't want to put all their eggs in one basket.

Back at Logan Airport, I ran into one man who doesn't necessarily trust the government to make the right decision.

Ivor Benton was on his way from Boston to Columbus.

Mr. IVOR BENTON: I don't think they're safe.

KNOX: What are you worried about?

Mr. BENTON: Well, what do you expect them to tell you? Do you expect them to tell you it's unsafe after they've spent millions of dollars for them?

KNOX: Benton says Toyotas were supposed to be safe, and Children's Tylenol, so he's learned to be skeptical.

Richard Knox, NPR News, Boston.

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