@bennetthecht
Basically SBRT photon is kind of now a bit older tech. So called by some SBRT proton is often very advanced new machines out there, but the name is kind of a misnomer, they are proton systems in a smaller format. Proton, or so called SBRT proton is the way to go. I worked on many medical devices and systems, so as an engineer working to get things where they need to be here is my rating of just the machines out there. top is best, bottom is not the best or least best since sometimes we have no say.

1 Proton therapy (sometimes called IMPT) & so called SBRT Proton. This includes Varian Probeam, or Mevion + similar, or large-scale proton such as Hitachi and others
2 MR Linac – MR based adaptive photon, MR Linac consortium/Phillips, MRIdian ViewRay, Elekta.
3 Varian Truebeam and Adaptive ones like Varian ETHOS – CT based, or CT with adaptive. Some places don't think the ETHOS is that great.
4 SBRT cyberknife type or photon
5 IMRT

There are other way to handle PCa but were it my choice proton as far as the radiation types, lowering side effects, handling cancer, and machine development. I should say even in proton there are ones coming out all the time that improve it, the Varian Probeam is new but there is a even newer Varian Probeam to some sold. Ask what machine they have if they will tell you.