Cindy,
Please keep in mind that the first two weeks following the end of radiation are often the toughest. Given your Dad's condition, you need to figure out how to get nourishment in him so that he can recover more quickly from the treatments, especially in the next few weeks.

I agree with the others on this message thread, you need to talk with the nutritionist at your Dad's facility, or another doctor. Often facilities will have an oncological nutritionist who specialized in these types of problems. At the very least, he should be getting some hydration intravenously if he's unable to swallow and has no feeding tube.

There are a number of possibilities for improving his nourishment and you may have to create a fuss to get somebody's attention. Good luck. - Sheldon