2 points here:
1) When I got radiation, they had me
empty my bladder before each treatment in order to hit the upper rear area where the gland had been where that pesky 1mm positive margin was. I had a treatment that was different from some of you guys, but that is how it was done to me.
2) My little guy often just sucks right up into my body cavity like a Sumo wrestlers' can, I have to fish for him when I gotta pee sometimes. I too think (beyond the atrophy) that cutting an inch out of the urethra then stitching it back together would tend to pull it back in.
Sometimes reality looks different than the pictures in the book.