Amy,
Like Cathy, my experience was that just about everything tasted lousy. Those things I could taste didn't taste right (vanilla ice cream tasted like a stick of butter).
The things I had to avoid included , of course, anything spicy, but you might be surprised at the foods which became spicy. I couldnt go near spaghetti sauce or marinara. Ketchup is still bothersome. Anything with acid such as vinegar in it would burn terribly. I had to get creative with gravies and sauces.
I did it without a PEG tube, so despite the flavor or lack of flavor, I had to get about 2000 or more calories and 2 liters of fluids down each day. Toward that end, I put a whiteboard on the refrigerator, and logged in all of my fluids and calories each day. This proved to be a pretty good motivational tool ( and it kept my wife on my case to keep hydrated and fed).By the end of RAD Tx I couldn't choke down all that fluid every day, and was getting at least one liter thru my port. My insurance covered periodic visits from a home healthcare nurse to hook up the port, and I hooked up the IV bag every day.

The bottom line though is that it's absolutely critical to his recovery that he get those calories and fluid every day. Calories that the body uses to rebuild from the damage caused by the radiation.
I have no better recipes than those that have been posted here before. Sorry.
My best wishes for a speedy recovery.

Good Health,

Chuck