Your timeline is similar to mine. In my case, I've ended up having just about every diagnostic test there is because my PSA is high enough to strongly suggest spread, but they can't find any. However, some of the tests took months to arrange. I'm still at least a month or two away from RT.
Presumably your dad has been on hormone therapy (HT) all that time? This is normally used before RT because it improves the chance of the RT catching all the cancer cells. The HT drives his PSA down, and the lower it is at the start or RT, the better the outcomes, so don't think of it as wasted time.
One thing I would get checked over this period is that his PSA has gone down significantly.
What was is PSA at diagnosis, and what is it in the most recent test?
If you haven't had a recent PSA test, ask for one.