[sstone]

The document was linked here before but is very detailed and interesting, even naming specific issues:

A) The large population of older travelers, >65 years of age, is particularly at risk from the mutagenic effects of the X-rays based on the known biology of melanocyte aging.

B) A fraction of the female population is especially sensitive to mutagenesis provoking radiation leading to breast cancer. Notably, because these women, who have defects in DNA repair mechanisms, are particularly prone to cancer, X-ray mammograms are not performed on them. The dose to breast tissue beneath the skin represents a similar risk.

C) Blood (white blood cells) perfusing the skin is also at risk.

D) The population of immunocompromised individuals--HIV and cancer patients (see above) is likely to be at risk for cancer induction by the high skin dose.

E) The risk of radiation emission to children and adolescents does not appear to have been fully evaluated.

F) The policy towards pregnant women needs to be defined once the theoretical risks to the fetus are determined.

G) Because of the proximity of the testicles to skin, this tissue is at risk for sperm mutagenesis.

H) Have the effects of the radiation on the cornea and thymus been determined?

[jrockway]

That's fine though. Society has already determined that 3000 people dying in a terrorist attack is much scarier than 500,000 people that die every year from heart disease. Otherwise we'd be spending money on encouraging a heart-healthy lifestyle rather than preventing someone from bringing a toothpaste-bomb onto a plane.

It's clear that if we can save 200 business travelers and vacationers from incineration, it's worth killing off a few senior citizens. Won't someone please think of the children?

(Hey, this isn't my policy. If someone asked me, "is it worth hurting someone to possibly save someone else", I would have said no. But nobody ever asks me about these things!)

[pygy_]

I've been told by an engineer friend of mine that the radiation dose these scanners deliver was dwarfed by the in-flight cosmic irradiation.

He didn't give me numbers, though. It would be nice if a radiotherapist (or another expert) could chime in on this topic.

----------------------------

edit: answering my own question: he's wrong.

from [1] :

>The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv.

> Other experiments, or dose rate measurements with the neutron dosimeter, consisting of LR-115 track detector and boron foil BN-1 or 10B converter, were performed on five intercontinental flights.

> Comparison of the dose rates of the non-neutron component (low LET) and the neutron one (high LET) of the radiation field at the aircraft flight level showed that the neutron component carried about 50% of the total dose.

> The dose rate measurements on the flights from the Middle Europe to the South and Middle America, then to Korea and Japan, showed that the flights over or near the equator region carried less dose rate; this was in accordance with the known geomagnetic latitude effect.

[1] http://www.sciencedirect.com/science?_ob=ArticleURL&_udi...

[fluidcruft]

The PR video/slideshow at the last checkpoint I went through said that the dose was safe because it was equivalent to being in the airplane for 3 hours. This presumably was meant to be comforting, but in my mind I was computing a 3hours:3sec ratio and trying to remember if time-dose averaging was appropriate (I work in MR, and it's been a while since my ionizing radiation course). I was not asked to go through the machine, but I would have refused simply because of the flippant tone of the 3hrs in the air claim.

[uvdiv]

No, actually your data validates him. Maybe you are confusing 'm' with 'μ', that is, milli- (10^-3) with micro- (10^-6)?

>The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv.

1.64 mSv (milliSieverts) / 500 hours = 3.28 μSv/hour. A 3-hour flight is 10 μSv.

For comparison, the FDA letter [1] linked in another comment here cites the effective dose of the backscatter x-rays as 0.25 μSv.

The cosmic ray dose from a 3 hour flight is 40 times that of the backscatter x-ray. Pretty much "dwarfs it".

(Note that while the FDA letter says the effective dose is 0.25 μSv, the footnote there (11) says that RapiScan is <=0.05 μSv. Not sure how to parse this -- maybe the 0.25 μSv is a regulatory definition, not the real dose. An NPR article [2] I cited earlier claimed 0.02 μSv, consistent with that <=0.05 μSv figure.

While I'm in these parentheses, NOAA has a table [3] of cosmic ray doses as a function of altitude. Pretty much consistent with your source -- 3 μSv/hr at 30,000 ft, 6 μSv/hr at 40,000 ft).

[1] http://www.fda.gov/Radiation-EmittingProducts/RadiationEmitt...

[2] http://www.npr.org/templates/story/story.php?storyId=1268330...

[3] http://www.swpc.noaa.gov/info/RadHaz.html

[pygy_]

Indeed. I know the difference between µ and m, but I missed it here.

/hides

[aperiodic]

The health risks can't just be quantified by the overall radiation dose. It depends on how that dose is deposited in the subject. The letter raises the concern that the since almost all the radiation is absorbed by the skin, the dose to your first centimeter or two of epidermal tissue may be fairly high. If the calculations that concluded the devices were safe assumed that the radiation was evenly distributed throughout the body, then the safety of the devices could be suspect.

[pygy_]

Thanks for the details.

I could not find the energy of the X-Rays used for these scans, but they would likely be low-energy (high energy rays don't scatter much), hence absorbed mostly superficially, as you said.

[tomjen3]

Maybe, but unless they remove radiation, they give out too much for what they are worth.

Cancer machines are bad for you, say no to cancer machines.