Prior to the three current PSMA PET scans (tradenames Illuccix, PYLARIFY, and Posluma), there were a number of PET scans that didn’t rely on PSMA. Some are still backups in case PSMA doesn’t work:
> F18-Fluciclovine —> Axumin® is the go-to these days other than PSMA. (Insurance still covers it.) Axumin doesn’t rely on PSMA. Axumin works by exploiting the fact that prostate cancers absorb amino acids at a much more rapid pace than normal cells. Axumin is made up of a radioactive tracer linked to an amino acid. Cancer cells absorb the amino acids more avidly than normal cells, so when Axumin is used, the radioactive tracer concentrates inside the tumor cells. When the patient is imaged, the areas that have a high concentration of the imaging agent signal the location of the cancer in the patient’s body.
> Choline C11–> works well for detecting prostate cancer; not sure who besides Mayo used it.
> F18-FDG —> Didn’t work so well for detecting prostate cancer (unless the cancer was very advanced); but, it did great for detecting lung and brain cancers which are more avid for sugar (glucose).
> F18-NaF —> worked well for detecting prostate cancer, but not sure if insurance still covers it.

You might consider asking your medical team what scan they use as backup if PSMA doesn’t see any known cancers.