[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.