But they are not really exposed to the elements while up there. How much aluminium and airplane interior does it take to replace 10.000m of atmosphere?
According to the CDC, a west-east coast flight is about 0.035 mSv per passenger.
The average annual exposure per person in the US would be about 3.3 mSv (without medical radiation from xrays and such)[0], mostly from natural background radiation. There are high regional differences[1], could be as low as 1 mSv or as high as 20 mSv. Human made factors play a role as well, e.g. coal burning (e.g. in power plants) will dose people living close by with radioactive elements in coal ash.
Anyway, a busy crew member can do maybe the equivalent of 100 such flights a year, which would be roughly an additional dose of 3.5 mSv per year.
Their total annual exposure would then come out as double the average (US).
For comparison, an xray can be as low as 0.1 mSv for a chest one, but a whole body PET scan comes in at about 23 mSv.
So I'd conclude that being a flight crew member would of course somewhat increase your radiation-induced health risks, but maybe not as bad as people might think.
Looking at other health factors for crew members, like in-flight air quality, increased exposure to fuel (kerosene) fumes and burn products working in airports and planes, or work/sleep schedules might offer additional/better explanations for the increase in cancer in this group compared to the average population.
[0] the world average is about 2.4 mSv, Germany comes in at 2.2 mSv, Japan 1.5 mSv. Didn't find a good number for India, where the article author lives.
