Ellen - my husband found that my blender contoctions were generally easier to get down that the canned products - the difficulty with the canned products is that they leave a residue in the mouth. Ugh. See if you can get a referral to the nutritionist so you are sure he is getting the nutrition he needs. I use both dairy and soy-based products, with a packet of Carnation Breakfast Essentials, and some extra whey power - but review with your doctors!!!
Besides general health, weight loss is an issue because if you lose too much, the radiation mask will not fit properly, and they may have to replan the IMRT.
When my husband was going through his therapy, I thought in terms of a week at a time - and I marked on the calendar each radiation and infusion - one more down, less to go!