Sorry you're here.
I would suggest you push for a PSMA PET scan. 0.25 is a little on the low side - there's a chance the PET scan might not find the cancer at the low level, and some places would want you to wait until it was higher before the scan. If the histology found that the cancer had got out of the prostate via perineurial invasion, then it's almost certainly in the prostate bed, but the PET scan might pick up any that's got anywhere else, and in some circumstances such as pelvic lymph nodes, the radiotherapy target field can be adjusted to include them.
Salvage RT does work, more so when preceded with a PET scan. Sometimes it's given with HT, sometimes not.
Wishing you all the best in the circumstances, and do come back and ask anything else that springs to mind.