Welcome,Stray!
I also had GS 3+3 in a lot of my cores on both sides when I was 57. I talked to specialists in surgery, low dose rate brachytherapy, high dose rate brachytherapy, SBRT, protons, and IMRT. All of them had about
equal and excellent odds of curing me, 95+%. At the time (2010) we didn't have as much info on active surveillance as we do now, and mpMRIs were not prevalent, or I would have given more consideration to that as well.
Since all were about
equal in expected outcome, the most decisive factor for me was potency preservation. The best potency preservation numbers were from SBRT and HDR brachytherapy. Luckily, the most expert practitioners of each were nearby. I finally went with SBRT, just because it was easier (no hospital stays) and less expensive. 8 years later, I have no side effects of treatment other than loss of semen.
But we are all different, and each man has to assess what is important to himself. Here are some questions he might want to ask himself:
/pcnrv.blogspot.com/2017/12/questions-to-ask-yourself-in-deciding.html