OK, trying to be more specific: Many locations administering Proton Beam Treatment (PBT) have used a treatment regime of five treatments per week for five weeks for a total of ~25 treatments. Three places where that has been true (not sure today) were Mayo AZ, Seattle Cancer Care Alliance, Loma Linda Hospital, and California Protons (San Diego). Mayo in Rochester/MN uses a five treatment regime for 90% of their patients with localized prostate cancer - so five PBT treatment sessions spread over two weeks - so something like M,W,F, M, W. Its my impression (bears verification) that the total dosage for 25 or for 5 treatments is the same. My own treatment at Mayo Rochester was the five treatment regime. I had some urethra irritation after the second treatment for which I started and continue Flomax and I may have some bowel irritation that persists, but for which I would say that I am asymptomatic.
If the cost of treatment is the same (I don't know) then the incidental costs of being away from home somewhere maybe a deciding factor for some patients on not choosing a 25 treatment option and choosing a different therapy without realizing that PBT is administered in some locations according to a different approach.
All that said, patients and the nature of their disease are different so different therapies may be dictated by the nature of their prostate cancer, and/or other illnesses or state of health.
Hope that helps