Really sorry to see this. No harm asking about R223 but be aware that, in some cases, it increases the bone pain rather than reducing it which makes it a bit of a gamble as a treatment that is purposed to improve quality of life :-/
When you say RT & surgery are no longer an option, do you mean RT / surgery on the prostate or on the spine? Some men are able to have RT to the spinal tumours to reduce cauda equina compression (SPCC) and there are men who have had cement or pins in the spine but as you say, your case may be too severe.