Although the HIFU procedure is the same, mine was as a salvage treatment for failed RT whereas in your case I believe it was as a primary treatment. This does make a considerable difference because your ultrasound was directed through virgin Prostate, whereas mine had to go through the scar tissue and mess caused by the earlier RT. Also with increasing age there is likely to be more calcification.
However, like you, I had my HIFU in 2015 but my PSA has been rising very slowly but persistently since. An MRI showed I had a small tumour about the size of a grain of rice and the surgeon who did the TP Biopsy said he would do well to hit it, although in the event he did. Interestingly, although my Gleason was still 7, it has gone from 3+4 to 4+3, so the percentage of higher graded cells are now the majority, at least in the core found. In January of this year my HIFU surgeon agreed to do a repeat HIFU. Another date for this (14th December) was only given to me yesterday after I had complained about various oversights and two previous cancellations that had caused the delay - a story in itself! I will try to establish whether the small tumour is in the same place and the previous HIFU was ineffectual. Is is possible that I could have a Prostatectomy with almost 100% risk of permanent incontinence as it was put to me but I believe this repeat HIFU will otherwise be my last chance of a Prostate confined treatment. I have already refused HT but accept this may be required if this second HIFU is unsuccessful.
In your case it is possible that the HIFU did not completely eradicate your tumour and it is regrowing, one that was previously regarded as insignificant has become significant, or a completely new tumour is forming. You would not have been offered HIFU if it was thought you had PCa cells outside the Prostate but this could be the case now, although it is unlikely. It's best if you wait until the result of the biopsy is given to you and what you are offered. We would like to share this information when available.