Rising PSA after SBRT - worrysome or to be expected?

Five years ago, I was diagnosed with Gleason-9 PC and had a prostatectomy.

Shortly thereafter, I had a biochemical recurrence and had 39 IMRT treatments on my prostate bed and pelvic region. I also had 18 months of Firmagon.

One year later, I had another biochemical recurrence and had SBRT on my Lumbar + Rib. In addition, I had 6 months of Eligard.

One year later, I had a PMSA/PET scan which revealed a metastasis on my sternum. I subsequently had SBRT on this lesion on my Sternum (but no hormonal treatment).

For my most recent SBRT on my sternum, my PSA was 0.75.
After 3 months, my PSA rose to 0.81.

Is it considered normal for my PSA to rise 3 months after my sternum SBRT?

How long would you expect my PSA to become undetectable or near-undetectable after receiving the sternum SBRT?

Thank you very much,
Mark