It's sound bl00dy good to me - I'd be well chuffed.
I was PSA 58 @ referral, T3b N0 M0 locally advanced, and I have had HT + RT + continue on HT, and myself I am now PSA 1.0 at 6 months post RT, and pretty happy with that.
Not sure how low it might eventually go, but doesn't matter too much about the minimum, just that it stays down there whatever that value might be.
Congratulations, enjoy your good result.
Regards
Grahamr