This was definitely not explained thoroughly if at all when side effects were discussed. Thanks for responding.
Surgeons don't often- seems to me- bring these side effects up pre-op. I don't know why your radiation guy would be blaming the radiation, when it is a well known complication of surgery. At least, well known to those of us who have had surgery. Though I'm sure radiation can add to any problems, or have it's own set of problems.
In addition to the section of urethra which is cut out, if normal erections are not soon restored- or at least any erection even if caused by pills or injections- lack of blood flow to the penis very often results in shrinkage, atrophy. An inch or 2 is not uncommon. I think if more surgeons spelled this out pre op, along with other problems common from surgery, at least when other options are available, there would be a whole lot less surgery. Again, assuming other options were available. And they usually are.