As the person on this board with the second highest amount of radiation, I fully support your husband's decision. Of course you love Him, but radiation has never improved anyone's quality of life. Reread Christine's answer to your first two posts about 70 and 80 year olds. At 90 let it go as the pain and issues will rob him of quality of life.
Explore hospice and palliative care so you can both enjoy his remaining years.
In my opinion, if your tears make him change his mind, you will both regret it.
I am so sorry that this has happened to you
Chram