Just a follow up to your reply. I asked my MO at JH and his very experienced NP (Dr. Pienta and Diana Reyes NP) what the next steps would be. They said that from their experience treating men in a subgroup like me (high grade cancer G9, very limited spread, excellent response to initial triple therapy with undetectable PSA) that about 70% remain undetectable after about 3 years (I don't think they have reliable data further out) and 30% will see PSA rise as testosterone rises. If PSA goes up they will wait until it hits 0.5 and then repeat the PSMA PET. If the PET shows another site of spread they will use SBRT to obliterate the cancer +/_ short 3 month course of Lupron.
I don't believe there are set-in-stone protocols for men in my position at this time due to the rapid evolution of treatment and the large number of trials ongoing. For me, that is why I went to someone with extensive experience, heavily involved in research, treats almost exclusively prostate cancer, and treats patients individually based on their circumstances rather than following set protocols (Standard of Care-which lags the curve of latest trials etc).