What specific dietary changes do you recommend for patients undergoing H&N, CNS, or GI RT?

I would leave Boost and Ensure as the absolute last recommendation possible. This goes for Carnation Instant breakfast as well, which is mostly made up of sugar and high fructose corn syrup. These supplements are poor sources of nutrition for anyone, let alone cancer patients. As cachexia is a state...

For patients undergoing rectal radiotherapy, I would recommend avoiding large amounts of high roughage: nuts, popcorn, crunchy raw fruits and vegetables. This may help with frequency and urgency of stools, both during RT and (sometimes) long-term afterwards.

Bob Myerson