Hi Jim,
I just completed IMRT three weeks ago. I asked the oncologist just how low would the PSA go since there will be (is) still viable prostate tissue after radiation. His comment was anything below 1.0 and steady would be considered good. As you can see from my signature I am also taking hormone treatment and my PSA was .82 before beginning the radiation. My oncologist says that the hormones will keep the PSA low and I will most likely see a rise when I discontinue the hormones in about 16 more months. After that the PSA should decline and level off if the radiation has been successful. If not, then I deal with that when the time comes.
I have read some other information that indicates the longer it takes to nadir and the lower the nadir the better the outcome and lower the chances for reoccurence. Taking all of this into account I do not think that you or I will join the zero club any time soon.
If it helps at all I have a friend whose dad had radiation treatment 28 years ago at age 70. When I asked if PCa is what he died from she said he is still living on his own but has slowed down some since he fell off the roof while doing repairs a few years back. I don't know about you but I like those kinds of stories. 
Best wishes for continuing success.
Don