Mark,
My experience with IGRT -
1) I was taking Cialis already when I started RT. It was causing what I thought was very minor low back pain, but when trying to stay perfectly still, it wasn't pleasant. Two solutions worked for me - still taking the daily Cialis, take an ibuprophen about 2 hours before the session, or take the Cialis in a bigger dose once Friday after the session was done.
My theory is that if the radiation does something negative, if I'm in better shape to start, I'm better off in the end.
Casey is right - for many, wait and see is pointless with the ED drugs. If you are expecting magic, well, you may be disappointed. You have to take matters in hand, so to speak.
2) My uro says the minimum wait from surgery to RT is 18 weeks. At that point I was at 1 pad per day. Over RT it worsened to 3-4. Now at 9 months from RT I am back at 1-2 per day. So yes, my incontinence worsened over time compared to before RT.
3) I had my last PSA before RT the week before all of the planning started for RT, and my next one the week after it ended. The uro / RO waited for one month after RT ended, saying anything closer was inconclusive. My GP slipped one in earlier in my 6 month blood work. There was no discussion of impact of the CT scan, and I can't see how it would make any difference (not a doctor here).