You should NEVER put film into checked in luggage. Always take it as carry on. The Xrays for checked luggage will destroy your film even in the xray proof bags.
Definitely, checked baggage gets a much higher dose than carry-on.
I got an "airport x-ray proof bag" by
Hama for something like $5, put all my film in that in my carry-on last time I went somewhere. They picked up "something not right" and put my bag back through 3 times on various angles to try to see what it was before they asked me to open it (I was standing there watching). Once I took it out and opened it they let me off with it (better than last time I had to open all my 120 Delta 3200 to get it passed around and not xrayed), but the TX in my camera went through the xray 3-times unprotected (no ill effects that I can see, but the Bessa is mostly metal).
After a bit of googling it looks like those bags don't protect against
everything, but a) it's better than nothing, and b) it's a bit easier to convince dumbshits running the xrayer that it's film when it's in something official-looking like that.