If it came from the prostate than it is prostate cancer, not bone cancer and if this is the case it is not curable. I’m not sure what you mean about radiation not working as it usually works very well for pain. They could also try hormone therapy. Patients can survive years at stage 4, it really depends on if they respond to treatment.
EDIT: I understand. Prostate cancer usually does spread to the bone doesn’t make it bone cancer.