Hi debz76.  Welcome to the forum.

I am not a doctor. I am a prostate cancer patient who had a radical prostatectomy in 2010. I've also been involved since then with our local prostate cancer support group.  This means I've picked up a lot of information along the way. 

I'm not an expert on what happens after radiotherapy, but I do know that the PSA does not drop to its lowest level until 12-24 months after treatment.  In the first few weeks after treatment, there is a rapid drop from the pre-treatment level.  I've managed to find a couple of graphs of "typical" PSA values versus time after treatment, and it's quite clear that the first few months are going to subject to a lot of uncertainty due to the shape of the curve.  Your father's PSA is somewhat higher than "typical", but not outrageously so.  A curve might be "typical" but that does include a lot of scope for individual variation. There is certainly no immediate cause for concern, particularly if the next reading (after 2 months) shows a lowering.  As I said earlier, it can take up to 24 months (or even longer) for PSA to reach its lowest value.  I know it's difficult, but try not to worry.

Note that the decline in PSA after radiotherapy is completely different from that after surgery.  After surgery, PSA drops like a stone and should be < 0.1 (less than 0.1) six weeks after surgery.  Don't get these confused in your mind. 

Regarding PSA tests. I always arranged with my GP surgery to have a PSA test 7-10 days before my hospital appointment.  This mean that I could pick up the result a few days before the appointment and if necessary I could tell the consultant the result! 

Best wishes

Telemando