When I was going thru treatment, my rad onc told me my throat would feel like there was broken glass in in toward the end of treatment. He was right. I had 33 radiation treatments and the last week of treatment was tough. I was unable to swallow anything for about 2-3 days when treatment ended. I remained functional throughout my entire treatment and did not get a feeding tube. Is your dad on his 12th treatment or is he finished? This was my experience. I hope it helps.