@clevelandguy
You may say this Has been used for years, But it appears that it is very rare.

I attend nine prostate cancer meetings every month. I’ve been attending nine for about two years and I have attended four weekly meetings for about five years with one group. I’ve been coming to the Mayo Clinic daily for almost 2 years. Six of those monthly meetings are just advanced cases.

I have never heard of anybody saying they had proton radiation to an area that had already been treated with a lifetime dose of radiation to a prostate or any other area. One of the online groups I go to weekly has almost 50 people show up every week, This week there were three brand new people annd about 10 others that wanted to talk about their current cases. No one mentioned having proton to an existing area, Never heard of it before from anyone.

It may be occurring in some places, but it is rare to put it mildly and from what I have read it is experimental. Hard to say what the long-term consequences are.