The saying goes "Radiation, the gift that keeps on giving". Yes, actually for a while he will feel worse but that tapers off. Basically, the inside of his throat continues to cook for a while after radiation and then takes it's sweet time healing. Food will probably taste strange, if not dowright awful, for anywhere from a couple months to (in my case) a year and a half. I spent that time living on Ensure Plus and fruit smoothies as solid food tasted awful and my mouth was really dry, and still is dry. Biotene maks a whole line of products to deal with dry mouth which has made a huge difference for me, It's available at most pharmacies and supermarkets. Well, however long it takes, most things do improve, and those that don't, he'll come tothink of as the "new normal". Best of luck on Dad's recovery.