Welcome to the Board and I'm so sorry about your dad. How old is he (you said elderly). I think the treatment is likely more difficult on older people but there are vast differences in how people cope physically and psychologically. He should be assigned a dietitian as part of his medical team (if not right away, request one) and this person will prescribe a liquid feeding product to be used with the tube. Anything he can eat by mouth for as long as possible is important including drinking water and other liquids. My husband used the tube for extra water to keep him hydrated once his mouth and throat started to hurt.