If your Dad has only a single metastatic lesion in his spine he has what is termed oligo metastatic disease (i.e very limited). Current aggressive treatment is SBRT (usually 3 treatments at high dose) to that area with curative intent. Yes, ADT is part of that plan. I believe current standard is triplet therapy to try and eradicate as much micromets as possible with the radiation killing the tumor visible on the PET. If his PSA becomes and stays undetectable, some MO and RO will stop the ADT and follow the PSA. If another met or 2 pops up, rinse and repeat-whack a mole.

Just my experience.