I am on my final week of proton therapy for prostate cancer and have had no side effects. Several others have just completed their treatment and they also have had no issues. Most doctors will not tell you about proton therapy and it's up to you to do the research. I am so glad I chose this option. The advantage of proton therapy is the radiation can be controlled so the majority of the dose goes into the prostate unlike conventional radiation.
As a result only a small amount affects other organs. The doctors also inject a gel called SpaceOar which pushes the rectum away from the prostate which minimizes the amount of radiation that it is exposed to. Everyone that I have spoken too is very happy with this treatment because there are little to no side effects. Definitely check into this before making your decision.
Have you had urinary control since prostate cancer surgery?