After recurrence a PSMA PET scan is definitely called for. The problem is that your PSA being so low it is unlikely anything will be found. I do know one person with a PSA as low as yours, whose doctor was having them get a pet test every three months, Because if something is growing, they can see it. In your case, if There is a significant metastasis it could be seen.

You are correct it’s usually below detection at that PSA level.

The reports you have gotten showing no spread are really not relevant if you actually are having reoccurrence, it could happen anywhere in your body. One thing people don’t realize is that when the cancer starts it sends dormant cells throughout the body to all different organs. At some point they can start to grow and become metastasis. As a result, you could have almost anything in bone or tissue.

I like your doctor being careful about waiting for your PSA to rise more, But the thing is when you have surgery, your PSA should stay undetectable. In your cases, it might come up a little and not be anything, but that is really unusual. As long as you have salvage radiation in time, you would not normally be required to have ADT. It depends on how quick your PSA is rising and whether or not the PSMA PET scan found anything.

Here are the recommendations of the American Society of clinical oncology for what to do when the PSA starts to rise after having a prostatectomy.

From Ascopubs about what PSA to do salvage radiation.

≤0.2 ng/mL:
Starting at this level maximizes disease control and long-term survival. Patients treated at PSA < 0.2 ng/mL achieve higher rates of undetectable post-SRT PSA (56-70%) and improved 5-year progression-free survival (62.7-75%).
Delaying SRT beyond PSA ≥0.25 ng/mL increases mortality risk by ~50%.

0.2–0.5 ng/mL:
Still effective, particularly for patients with low-risk features (e.g., Gleason ≤7, slow PSA doubling time). The Journal of Clinical Oncology recommends SRT before PSA exceeds 0.25 ng/mL to preserve curative potential.

0.5–1.0 ng/mL:
Salvage radiation remains beneficial but may require combining with androgen deprivation therapy (ADT) for higher-risk cases.

This article discusses the above;
https://ascopost.com/news/march-2023/psa-level-at-time-of-salvage-radiation-therapy-after-radical-prostatectomy-and-risk-of-all-cause-mortality/