US carry on scanners aren't all film safe which is why they'll allow hand checking, however in the UK/Europe they are safe and virtually all airports will refuse to hand check film. Even if you hand them the film boxes for checking they will still scan the film, there may be a the very odd exception.

Unlike the UK/Europe the US has a large number of smaller commercial airports and not all have modern scanners, my own experience was that even in a major hub airport the scanners were years old compared to the ultra modern scanners I've seen in UK/Europe, South Aerica etc.

Ian