My post op psa was 1.5 and rapidly climbing with a doubling time of 9 weeks. They offered RT but I’ve refused 4 times now as with that result they suspected further spread. This seems possible in your case as you’ve had SRT but now it’s climbing again already. My psa is expected to be over 100 in January and I’m having zero treatment as scans indicate nothing. I’ll hold off HT and Chemo as long as possible as enjoying recovery. Ask for a PET scan