Small Minnow,
I know this is a very difficult time for you and your friend. Remember that the effects of radiation are cumulative and seem to peak about two weeks after the treatments end. It is a long, slow recovery process. Hopefully your friend will start to turn the corner and you will see some signs of improvement. The more hydrated and nourished the hospital can keep him, the faster he'll start to feel better.
Best wishes, Sheldon