Wired lets me down with some airport body scanner fear mongering:
TSA admits bungling of airport body scanner radiation test:
The Transportation Security Administration is reanalyzing the radiation levels of X-ray body scanners installed in airports nationwide, after testing produced dramatically higher-than-expected results.
The TSA, which has deployed at least 500 body scanners to at least 78 airports, said Tuesday the machines meet all safety standards and would remain in operation despite a “calculation error” in safety studies. The flawed results showed radiation levels 10 times higher than expected.
Read a little more deeply, and it turns out that the problem is not that the machines are emitting 10 times higher than expected radiation – it’s the much less hazardous (and less sensational) problem that the technicians testing the machines forgot to divide by 10.
Apparently, the radiation emission from each machine was supposed to be measured 10 times, and the average of these 10 tests placed in the report. Instead of the average, some technicians didn’t divide by 10 – they reported the sum of all 10 tests, not the average. Hence, a report that makes it look like the machines are emitting 10 times more radiation than they are supposed to.
In another recent article, Wired gives plenty of space to scientific critics of the these scanners, and almost none to the response by the FDA and the scientists who performed the safety tests. For example, Wired quotes UCSF biochemist John Sedat:
Sedat counters that the mechanical beam’s intensity level has not been published, making it impossible to evaluate the safety claims. “I want a real hard number in terms of photons per some unit of area,” he said. “The one physical quantity that is crucial for determining what dose a person is getting, that data is missing.”
Moreover, standard medical X-ray machines disperse radiation throughout the body, whereas the airport scanners penetrate to about skin level. That means there is a high concentration of radiation on a single organ — the skin — which was not accounted for in the Johns Hopkins report, Sedat said.
The “correct way” to test any such technology, he said, is to use mice “and appropriate tissue-culture cells and see if there is a biological response.”
“That kind of stuff has never been done,” he said.
Wired quotes the CEO of the company that manufactures the scanners in response, but not the scientific response to these criticisms by the FDA, which I find convincing:
Fourth is the concern that “the relevant radiation quantity, the Flux [photons per unit area and time (because this is a scanning device)] has not been characterized.” We disagree that flux is the appropriate quantity. The air kerma (or skin entrance exposure) for one screening can be determined by a direct measurement of the total charge produced in the air contained in an ion chamber during one complete screening when the meter is correctly calibrated14. Additionally, measurements to determine the amount of material required to reduce the intensity of the x-ray exposure by half16 are necessary to convert air kerma (or exposure) to effective dose15. These measurements can most practically be made —and indeed have been repeatedly made— at locations where these products are installed and can be made without altering a scanner’s normal operation. These are the same sorts of measurements made to characterize the output of medical x-ray systems17.
Fifth is the assertion that “if the key data (flux-integrated photons per unit values) were available, it would be straightforward to accurately model the dose being deposited in the skin and adjacent tissues using available computer codes [. . .]” In fact, we have done better. FDA and NIST used software called PCXMC18 to estimate the individual organ doses and to calculate effective dose. This analysis was part of an evaluation performed under contract for TSA. The input information required by the PCXMC program required considerably more information than simply the x-ray flux. Its parameters include 1) the x-ray tube anode angle, 2) anode voltage, 3) total filtration, 4) x-ray field size, 5) location of the field on the body, 6) focus-to-skin distance (FSD), and 7) entrance skin exposure. Every parameter was measured, calculated, or verified by indirect measurement. The modeling results revealed that the dose to the skin is approximately twice the effective dose19.
We don’t need more mouse and tissue culture studies to determine the effects of this type of radiation exposure, and Sedat’s insistence on getting a photons per unit area number is unnecessary.
I share other concerns about these scanners: privacy issues, and the odd choice not to go with a non-x-ray alternative, but I’m not worried about body scanner induced cancer.
See also this previous post.
The Finch and Pea 
And, as we have pointed out here before, even “acceptable” risks become intolerable when there is no demonstrable benefit.
Agreed… the current policy probably has something to do with the political influence of manufacturer of these Rapidscan devices, and less to do with sensible cost-benefit thinking.
Precisely. The safety issue is, in some ways, a distraction. Even if the devices are perfectly safe to any reasonable degree, there are principled reasons to be opposed to such policies and intentionally terrorizing people into compliance.