Eating is always dicey right after treatment...sometimes due to pain, sometimes due to tastelessness....sometimes (like your dad...tastes awful and texture is stinky). I know one person who didn't have anything but smoothies for 7 months post treatment, and then everything started working again. I wanted my Peg out so bad, I wore steel toed work boots for a weigh in....I suffered from the plaster board symptom...that's what everything tasted like to me.
High calorie smoothies might be worth a try...
p
PS...My nose was so good during radiation, I could have tracked a human across a field and found him
.