What is "Medical Necessity" for CMS and PSMA-PET

Does anyone know what the Medicare guidelines are for deeming medical necessity for a PSMA-PET scan.

https://www.cms.gov/medicare-coverage-database/view/ncd.aspx?ncdid=331

This^^ shows they will not pay for "Diagnosis and Staging", but will pay for "restaging and monitoring for treatment"

Since it is commonly assumed Gleason 6 does not spread, would they cover if Gleason 6 is found on biopsy? What about a Gleason 3+4?