Susan,
I underwent 30 radiation treatments after surgery for a tumor found on the left/base side of my tongue. I completely understand the swallowing and taste issues your father is dealing with. I too got to the place where I couldnt' take ANYTHING else by mouth and although I was afraid I wouldn't be able to swallow again, I just couldn't do it anymore. I am currently 2 1/2 months from my last dose of radiation and just now able to do some light swallowing of liquids, pudding, applesauce, etc. I had a swallowing test completed last week and they said things look good but I'm still really swollen in my tongue and throat which could account for the difficulties I'm having.
My best advice, which is hard to hear, is he has to do this for himself. As frustrating as it is for you, you're right...the only control he has is over how he chooses to respond. I'm 31 years old. As much as I wanted to swallow, I couldn't do it. Everyone deals with this in their own way and everyone responds differently to the treatment. No one ever expected me to have the side effects that I did due to my age, but anything that could go wrong did and my recovery has been much more slow than I'd hoped.
Hang in there! Sounds like you're doing an amazing job!