I know how worrying it is when PSA starts to rise, as you say '...We waiting for PSA to reach 3 to 5 to make sure we can see the suckers wherever they are grrrr...'
Thing is when I was in that position back in 2013, my PSa rose 2 to 4, in 6 months and 4 to 6 in two months, at which point I had an appointment with the Consultant's assistant, I think they call them 'housemen'. The scheme they had in place at my hospital was that patients got to alternate, seeing the main consultant at one appointment, and his assistant at the next one. So I was only seeing the main man once a year. Anyway with PSA at 6 and rising rapidly the assistant 'houseman' suggested I go back on HT and I had no qualms about that.
He was also telling me at that time that because I had already had one bout of radiotherapy, there were no treatment options other than HT. So logically there was no point in further scans, because they were not going to do anything other than HT whatever the scans might show.
Later, having done a little research myself, and identified options such as cyberknife, and having sent them a polite and detailed letter, I ended up getting referred to another hospital for salvage HDR brachytherapy.
Then I had to have scans, indeed I had the full set of MRI/CT and Bone scans twice, not because they were so much looking for PCa, but because they were double checking that I was otherwise healthy and not about to die from something else.
They picked up interesting facts like I have arthritis, I had cysts on my kidneys, two different types of cysts on my thyroid gland etc, but none of the scans were of any use for finding the PCa as my prostate and surroundings were likened to a bombsite, they had to do template biopsies to find the actual cancer.
In the middle of all this, I actually got my 6 monthly appointment with my Consultant, he is a nice guy, I have every faith in him, but he has that habit I guess a lot of doctor's have, of looking at his notes and bringing himself up to date while you are sitting next to him. He read through my notes, and sort of asked me 'you went back on HT when your PSA got to 6?' When I replied yes, he said sort of talking to himself that he might have been inclined to let it go higher, he didn't say how high and I didn't ask.
I wish I had taken that conversation further because he was implying that when the PSA starts to rise there is some minimum threshold it needs to cross, before there is any chance of seeing a tumour on a scan, and presumably in my case with an irradiated prostate that was higher than 6?
Right at this moment I am feeling very uneasy, on paper I am doing very well, my last PSA was a mere 0.2, but I can sort of sense, a gut feeling, (I almost said a feeling in my bones!) that it is on the rise, quite how high it will be prudent to let it rise to before going back on HT is something about which I am far from clear.
I suppose it is a sort of bare knuckle ride, because the higher you let PSA go without treatment, the more chances of further spread, but as you say you need it high enough to see the suckers?
I don't know if any of this helps? But best of luck.