Try to remember that the HT is the main treatment, the Oncologist said to us that the Chemo is "the icing on the cake" in other words the HT is the main cake. If your Dad has to stop the chemo it is not a disaster. I think we tend to see the chemo as more important than it is because it is obvious, whereas the HT is not as noticeable. It is only very recently that they have started to give chemo early on as they found that in some cases it can help the HT work for longer.
Obviously something is working, probably the HT. When was the PSA taken? My OH had his taken just before the first chemo his had dropped to 1 from 66 just on the HT alone.