My research on proton vs photon with IMRT/IGRT was the same as JohnT states. The machine used in my treatment was the Varian but not the Rapidarc. Rapidarc is a recent development that speeds up the process but I do not believe makes it any more accurate. I have had very little in the way of side effects due to the radiation. The HT is another matter entirely.
Also my original research showed for "localized" PCa that radiation and surgery gave similar results with a slight edge to surgery at 10 years out. If you are considering radiation there are a couple of other photon machines as well. One is the Cyberknife. Somewhat new to PCa but advantage is shorter treatment duration. Five vs 45.
Look at all the options no matter how confusing before making the final choice.
Good luck to you.
Don