@robertov, in my case (stage 2 G9), even though PSMA PET scan showed no spread, adjunct external beam radiation was highly recommended for my treatment plan.

That recommendation was the same whether I opted for surgery or HDR Brachytherapy.

Before deciding, I consulted a surgeon (prostate specialist). In addition to RALP, he also recommended adjunct external beam as part of my treatment.

I think it's a risk vs reward decision.

At my age (72), I believe the long-term risks of adjunct radiation are outweighed by the benefit of a potential "cure". At the very least, for my aggressive prostate cancer, I believe adjunct radiation substantially delays a likely biochemical recurrence.