I don't have a lot of facts relating to radiation exposure for flight crews on long haul flights, but I do remember reading a report, about 6 or 7 years ago, when I was flying the MD11, about that subject. The one fact that remains with me, is that for every 4000 feet increase in altitude, your exposure to cosmic radiation doubles. So that always stayed in the back of my mind when flying for 4 or 5 hours at FL390, as opposed to staying down at 350. In fact, after that report came out, one of my buddies would state, "You can just call me Mr. 310 from now on, cause that was as high as he was going to go on the long flights, especially at the high latitudes, where you had very little atmospheric protection. Of course, we are supposed to be fuel sensitive, and fly high to save that precious liquid, and, I suppose help protect somebody's MBO points. But when you hear numbers like this, you have to just say, hmmmmm. But I will say, that I rarely flew above FL350 for extended periods after that. Something for you 777 guys to think about when you are sitting up there for 16 hours at a time, month in, and month out.