Prostate Cancer has spread to bones.

My prostate cancer has spread to my bones.  My prognosis is 6 to 9 months.

I have been offered Radium treatment which could help.

Should I  go ahead with this, what can I expect in terms of quality of life?  I realise that this treatment will not improve my life expectancy by much, but my main worry is how quickly my health & mobility will deteriorate. Is it likely to be gradual, or will I be comparatively fit for most of the time, reaching a 'cliff edge' near the end?

Any comments or advice from anyone who has been through this (or family & friends who have experienced this) would be greatly appreciated. 

Thank you.