Would you continue serial PSMA PET scans after 2 negative scans for patients with a persistently rising PSA post-RT?

Some context would probably be helpful for this. E.g., PSA >2 is different for a patient post-prostatectomy vs. post-radiotherapy. But, in general, if clinical suspicion of cancer recurrence/progression is high, and PSMA PET is negative, one can consider the following options:

1. There may not be a cancer recurrence. For example, PSA ~2 post-radiotherapy could be from residual benign prostate.
2. Cancer may not yet be macroscopic. For example, multiple foci of microscopic disease are growing, but none have reached sufficient size to be detected on PSMA PET.
3. Cancer may be macroscopic in size but has low PSMA expression. Common alternative imaging options include multiparametric MRI (of the pelvis, for example; whole-body MRI also has utility, tho...

No, I wouldn’t repeat the same imaging. Prostate MRI next, and consider biopsy of the prostate. If disease is present in the prostate, consider post-radiation salvage local therapy, such as HIFU.