I had a lower PSA of only 41, as a T3B cancer 6 years ago. My bone scan was clear too, and my Gleeson was 4+4 which is 8. I went through hormone therapy for 6 months, the radiotherapy (IMRT) for 7 weeks and they injected 3 gold seed into my prostate, so on every treatment day they could X-Ray me first, see the seeds and therefore where my prostate was, and adjust the RT beam to hit the centre of the cancer. The reason for the "seeds" is that the prostate can move up to 2 centimetres day to day, and the gold seeds allow them to fix the actual position.i also had to have a full bladder, and empty bowel before the Radiotherapy, which involved drinking water, and giving myself a micro-enima before each of the 37 treatment sessions, but it was worth it!
I had 2 more years of Hormone therapy, and now I am off all treatment. I only have a PSA test every 6 months.
The hormone therapy has its issues (hot flushes, lower energy, tiredness, being emotional and loss of libido), and the radiotherapy does have a few issues, but they are not too bad, and the radiotherapy nurses are there to help.
MY PSA now is 0.18.... I can live with that!
Hope your dad is lucky enough to have the good treatment I enjoyed.
Good luck to your dad...