I have had that from head to toe, travleottie. It is well studied but not well understood. I could bore you with years of details but the real key is improving blood flow while periodically checking calcium levels. There are many early intervention possibilities but with me, I was too little, too late. I don't know if I can reverse it or stop it, but I certainly have managed it beyond anything doctors thought was medically possible.
I was curled up in a ball, unable to sit up or stand up because there were no muscles left and it hurt from nerve pain head to toe. I emerged from hospice care and have put back 30% more body weight and mostly muscle. I just retired the last of the machines that helped me regain body functions.
Blood flow, removing nerve impingement, diet, cardio work, light resistance work and stretching are all part of the complex puzzle. It is a full-time job but it's working as long as I want it to. 5 days of nothing causes muscles to start shriveling up again.
Statistical outlooks given by several of my doctors says about 1/2 of 1% will get to the point of no return after radiation above 45 Gy to the upper chest to the ears. That would be maybe 30-40 people a year for our group. Numbers are only historical calculations based on what happened and not necessarily what will be.
Be well...but be diligent.