Hi Sandi,
I would suggest getting him on some glyconutrients (from Mannatech). They are nutritional supplements that will help strengthen his immune system. I personally know several people who have had chemo or radiation, or other procedures, including myself with a whipple, who take them and they seemed to have really helped. I credit them with saving my life and keeping me healthy. There are many people on these boards who have tried them with differing results, but I think they are worth a try. If he can tolerate milkshakes, they'll help him keep his weight up. Kim