Here is all I could find on it. I believe it says something under "Survival & Staging" that might help.
I do know that my daughter's grandfather has had prostate cancer for 10 years, is 82, and is still going strong. I'm no
RadiationTherapy for Cancerby
Cancer.govtherapy : External-beamradiationtherapy can be delivered by protonbeams as well as the photon beams... to a tumor ( 9 ). Protontherapy has not yet been compared with standard external-beamradiationtherapy...