Hey Brian, As usual I am looking thru the narrow lens of my own experience with IMRT 5 yrs after surgery.
From what I understand ( and I could certainly be wrong) proton radiation is usually given as ‘adjuvant salvage’ radiation immediately after surgery when there are known metastases directly outside the prostate bed or in the pelvic nodes.
These areas can, of course, be targeted and proton therapy is very effective at treating them and causing minimal peripheral damage. However, in cases such as mine, with rising PSA 5 yrs post-op and NO visible activity on PSMA I do not believe proton therapy would be as effective; there are targets (bed and nodes) but the radiation beams produced by proton radiation vary in intensity from the center (strongest) to the periphery (weakest) and you may overtreat one part of the target and undertreat the other.
IMRT offers more consistency thru its arc - which ironically is both its strongest and weakest points: it will fry everything evenly, but do more damage to other organs on the way in - and out!
It would be interesting to know if the men you met were in the adjuvant salvage or late salvage stage. Thanks for the post!
Phil