djbattle,
With general field radiation, such as the kind you say your husband is getting, it's possible to feel reasonably OK for 2-3 weeks, but please be prepared for it to get significantly worse at some point beyond that. Side effects such as dry mouth, thrush, mouth sores and skin irritation can appear rather suddenly, so it's best to be ready just in case. Your medical team should be watching for early warning signs of any problems and giving you the necessary medications to help cope with them. Nutrition and hydration are absolutely essential to enable him to get through this phase, so it's really important to track his intake each day.
Cathy