Actually I think you are safe inside the cockpit.
As you know, the massive centrifugal forces once the blades start rotating will throw all the radiation outwards. Beware of any manoeuvres causing re-circulation though.
The lead underpants might be useful if you haven't finished procreating but as you know, we helicopter pilots seldom get our leg over anyway due to the lack of a leg-opening flash uniform to wear, and the smell of AVTUR puts the ladies right off.
Hope this helps to alleviate your worries.
But keep the windows shut just in case, eh!