Metastatic prostate cancer is extremely painful for most men towards the late stages. The myth of a painless death is rarely achieved. The trick is balancing the meds so that pain is controlled without the man being in a permanently unconscious state - not something that hospital oncology teams or GPs are usually particularly skilled at. If not already done so, ask for a referral to the local hospice who are generally the specialists in pain control - or perhaps the pain clinic at your hospital, if there is one.
RT can sometimes be offered if one or two bone mets are causing most of the pain, or if the mets are making the bone unstable.