Hi Grant,
I was in a similar position to you having had failed RT. The Royal Marsden who had taken back my case then referred me to UCLH as a possible candidate for HIFU. Before taking the plunge, I asked a pretty senior consultant at UCLH whether I should consider a Prostatectomy instead. His reply was on the lines of yes if I wanted almost 100% chance of urinary incontinence, with the possibility of this being permanent. In view of this I proceeded with HIFU within the FORCAST trial. (Had the tumour been unreachable with HIFU, I would have had Cryotherapy instead).
A resultant fall in PSA following the HIFU showed that some, if not all the tumour had been ablated during the procedure but thereafter PSA began to climb again albeit very slowly. I was subsequently offered HT. I rejected this because I know the drawbacks of HT from having had 8 months back in 2007/8 before and during RT. Furthermore, I wanted HT to be a fall back treatment after all potential other treatment had been tried/ruled out. To cut a long story short, UCLH eventually agreed to do a second HIFU. This time PSA went down to 0.02 and 0.03 and a couple of years on was told no PCa could be seen in a follow up MRI and that I could consider myself in remission. (I know they will not do a further Focal Treatment should a tumour in my Prostate grow, which is always a possibility if there is still a Prostate but will take a view on how to proceed if this should happen).
HIFU does sometimes require a second attempt but I found it very easy, particularly after the catheter was removed after about a week. I had no side effects but already had ED due to previous RT. But I must stress this was my experience and as with other PCa treatments it can vary from one individual to another.
If I correctly recall, a member said there is a surgeon, I believe it was at Guys in London, who specializes in doing Prostatectomy on previously Radiated Prostates with less severe side effects than normally experienced. You might wish to investigate how accurate this is before making your treatment decision.