The photon v proton response is worth investigating. I am 72. I just finished week 1 of external beam radiation to my trachea. I have almost no symptoms. My trachea is where the cancer is left over, post total thyroidectomy.
You are 80 years old. God bless you. Don't give up. I have been told that most of our experiences during treatment are mental as well as physical. Perhaps you can do the treatment at a proton facility, and also have supportive counseling. I hope you see your 100th birthday. Read the book by Potts. I think he had cancer 5 times.