@dave27

Unfortunately everybody needs to check PSA for many, many years, no matter what were findings after surgery. At the beginning they will check his PSA every 3 months, than every 6 months , than if there is no change after a couple of years once a year and that is protocol for everybody. That shows you that no matter how good or how troubling findings are nobody is in "clear" for many years after either RP or RT . That is the nature of PC, unfortunately. It can be dormant for 20 years and than pop up again but one can only take one step at a time.
The most important thing is that your father does not have aggressive cancer to begin with and even if it comes back it will most probably be treated successfully. I know that this all is so hard to hear and I wish I can tell you with certainty anything, but unfortunately nobody can. There are statistics and there are "probabilities" but everybody is different.

The one thing that is kind of important predictive factor is PSA level. If it comes undetectable and stays that for a year or more, that would be very good sign. Sometimes it is very low but not undetectable, still, if it grows over time in a very slow manner, that is again good sign and he may have couple of years before deciding to go into additional "clean-up" treatment. If it comes up fast, it just means that treatment should be administered VERY soon.

I know that this all sounds overwhelming and it IS. Just make sure that your father has the best doctor that there is and also never shy of asking for a second opinion. It is common thing to do with any kind of cancer treatment and doctors completely understand that and many even encourage patients to do that.