I'm no expert but Brachytherapy not the gold standard for all cases.
I expect my cancer was too extensive. My initial diagnosis from MRI and then targeted biopsy was cancer on left side apex. As it turns out I had positive margins at the bladder base, and I think prostate bead.
As has been mentioned in other answers. There is a life time limit on RT. So can't have repeats on same area.
There are focal therapies that I don't know anything about. I have read these been repeated on different areas.
Jim