I was treated with SBRT, which is much more specific than IMRT, though not as much as Proton. I did suffer some radiation cystitis and proctitis (symptoms appeared a year later), but it wasn't too serious.

With IMRT, which is more of a blunt tool, I think the goal is to radiate the area around the prostate as well as the prostate itself (though as a layperson I could be completely wrong) — were they concerned about some local spread in your case? If that's true, then surgery probably wasn't an option, since you'd have needed the radiation anyway.

I think the choice for radiation would depend on which kind you're getting and why, rather than just a blanked yes/no decision. For me, surgery made no sense, because

1. I'd just had debulking surgery for the lesion on my spine to try to decompress my spinal column, and I had a lot of complications afterwards (including a prolonged ileus that left me unable to eat for 2 weeks).

2. The cancer had already spread (hence the spinal lesion), so simply removing the prostate wouldn't do much.

3. I was still in a wheelchair, so dealing with the acute post-surgery complications of a prostatectomy would have been very difficult (getting to the bathroom was already a complicated challenge involving transferring to a stair lift).

A lot of people experience very few side effects with SBRT, and they resolve quickly; I was an exception, but no regrets.