I had proton for a different cancer and there were patients there who were repeating appeals to their Medicare Advantage Plans for coverage. The md may have been exaggerating, maybe not exactly lying.
I've had cause to look at prostate cancer treatments recently. I'd like to suggest that you look at treatments with MRI guided photon. MRI guidance isn't available wth Proton, yet. I'm partial to the MRIdian Viewray, because the margins might be smaller than with other machines. The treatments are hypofractionated (higher dose lower number of treatments). It is usually five treatments 40GY total with hypofractionated and 28 treatments with proton or photon without MRI guidance.
The MRI guided treatments close down when there is target movement.
You should, though, talk to a proton specialist and at least one radiation oncologist. I found it easiest to have video consults and then travel for treatment.
Best wishes