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The health concerns of radiation exposure of backscatter X-ray have never been properly characterized at all. One specific concern that was raised with airport scanners is that existing methods of estimating safety limit dosage simply don't work with backscatter, which deposits the majority of radiation in the surface layers of the subject (i.e. in the person's skin), which has much lower volume (and therefore higher radiation absorbed per volume) than the whole body. (http://www.ucsf.edu/news/2010/11/5810/ucsf-scientists-speak-...)

The privacy concerns are peanuts compared to the potentially massive harm that the X-rays caused in terms of skin cancer susceptibility.

The worst case is pretty scary and regardless of the outcome, I think the government (we the taxpayers) will be on the hook for huge liability litigation in the future regarding these machines.

It has legitimate uses for scanning cargo, and I see little issue with imaging a car if there's nobody in it, but one of these things driving down the street irradiating everyone is potentially a massive health problem.

"I see little issue with imaging a car if there's nobody in it"

If you were to spend some time at a border checkpoint sitting in a chainlink cage(literally) in the accompaniment of other travelers as your vehicles are batch scanned you may change your mind. More so if that checkpoint happens to be located 100+ miles north of the border.

I think he is talking health concerns, not privacy concerns.

> The health concerns of radiation exposure of backscatter X-ray have never been properly characterized at all.

To amplify: The former head of homeland security profited handsomely from their approval. http://www.washingtonpost.com/wp-dyn/content/article/2009/12...

I wouldn't want to be in his shoes if there is ever a larger-than-average number of cancers in the TSA agents. Even if it is merely statistical fluctuation, his conflict-of-interest may come back to haunt him in ways he has not anticipated.

I may be more cynical than you but I'm pretty confident that being in his shoes won't be unpleasant whatever the outcome. The taxpayer will sort it all out.

Also, these scanners are not operated by trained radiologists, and I am highly doubtful that those who do operate them have been given adequate clinical training—much less care about the clinical ramifications.

"Honestly 0.1 μSv is the headline figure. What is the full body accumulated figure? I'm going to guess as much as .30 μSv per scan."

Should .30 be 3.0? Or...?

From http://as-e.com/products-solutions/cargo-vehicle-inspection/...:

"Dose to Cargo: Less than 0.1 microSievert (μSv) per scan (equivalent to 10 microRem (μrem)), at an average speed of 5 km/h (3 mph) at a scan distance of 1.5 m (5 ft). Should a stowaway accidentally be scanned, the effective dose is well below the ANSI specified limit for accidental exposure and is equivalent to flying two minutes at altitude."

In other words:

a) "Beam" is not over a small area but over the entire scanning area.

b) The 0.1 μSv dose is for entire cargo.

c) The total body dose in above case is therefore much below 0.1 μSv (because person is much smaller than cargo).

Also read this: http://www.medpagetoday.com/PublicHealthPolicy/PublicHealth/...

You can look at this the other way as well. The scanning beam only causes a low exposure at a point because it is scanning very quickly. The peak radiation is quite high. We know the dangers of cumulative dose because that is most useful in the case of low level exposure over a long time. Could it be possible that the risks are different for brief intense exposure?

http://en.wikipedia.org/wiki/Linear_no-threshold_model

If it holds, it's 'good' for the scanners because their high power shouldn't be penalized; bad for them because any dosage increases risk.

It is still rather contraversial but radiation hormesis is interesting to read about. Populations have been exposed to relatively high radiation levels from things like the earth (Iran and some places in the US among others), contaminated steel (Taiwan) and various medical procedures. These groups have not fitted into the linear no threshold model very well at all, and there is an argument that low doses may actually be a health advantage. http://en.m.wikipedia.org/wiki/Radiation_hormesis http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664640/

Edit: keep the body scanners and bomb scanner away from me please.

> Instead of reporting the total body accumulated dose, they report the dose a single scanning beam sweep induces over a small area.

A major problem radiation dosimetry has is definitions are easily confused. The NRC's dose limits for individual members of the public [0] dictate a total effective dose equivalent of 1 mSv a year. The confusing part is keeping all the numbers straight if it is an effective dose, effective dose equivalent, or a dose equivalent. I'll get back to why I bring this up in a second.

I do want to say that I don't see the reference you are getting the 0.1 μSv per 1x1 (cm square?) area from the article (just mentions a per-sweep radiation measurement but doesn't report what kind of dose that is). However, from your sources it actually doesn't surprise me they are reporting the radiation dosage that way, if they are reporting it as an equivalent dose.

An equivalent dose normalizes for radiation type. A gamma or X-ray is weighted much less than alphas (typically 1 vs 20 weighing factors, depending on what standard you follow). But the equivalent dose does NOT take into account what part of a human's body you are irradiating. If I had to choose between a pinky finger and my thyroid, you can probably imagine which one I would pick to be subject to irradiation. Instead, the effective dose accounts for the different parts of the body (and effective dose equivalent for both). This is why I suspect the manufacturer preferred the equivalent dose as opposed to the effective dose - they are normalizing for the type of radiation but not the part of the body they hit. There is the ICRP's notion of an "ideal adult" but each person's natural variation of geometry (height, girth, etc) would skew the manufacturer's number in some way. Of course effective dose is still imperfect as it contains a general biological potency assumption but it would mean a lot more to the public than a count of gamma rays and their energies.

> What is the full body accumulated figure? I'm going to guess as much as .30 μSv per scan.

That would depend on the van's speed, its beam patterns (spatially and temporally), the position of the person, etc. Honestly I can't tell if that is reasonable or not, but (returning to the NRC limits for the general public) keep in mind that the van would have to drive by you 1,000 times in a year to reach .3 mSv of your 1 mSv regulated limit with your guess. Of course, there are people out there that put lead-foil hats on and distrust the regulatory limit.

[0]http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/pa...