i assume you're referring to normal film in canister type. If it already has been thru many times, you can either use it as an experimental roll or throw away and get a new one.
high speed film tend to be more sensitive -vs- normal 100-400asa films
*(there were cases of funky rolls at least according to some sites i visited years back even when its film-safe labeled). *
With today's technology who knows. No one will guarrantee anything, so at least be mentally prepared if it comes back from the lab a little funky. On your part, i suppose it won't hurt (a lot) to carry a digital body or point-n-shoot as backup.
I second that; multiple exposure to x-ray will likely do the film in despite modern machine being film-safe. If you put your films in a lead line bag, the officer will likely increase the intensity to see what are inside and this may also harm your films.