It's a magnetic field, no? Is there any particular radioactive component? I'd be more worried about the acute effect on the plane's electronics, the whole point is they disrupt electrical systems.
I don't know the numbers on actual dose for something like this, but I'd expect that it's "elevated radiation risk" in much the same way that getting a CT is. If you get scanned 10,000 times, there's a pretty good chance you'll die from cancer, but mostly it's just a slight statistical increase in your odds.
I read some time ago that normal routes are fine but if possible people should avoid polar routes. Then again I think airlines nowadays track these exposures and adjust routes.
