DonnaJean,
You may want to fight harder with your stubborn hubby to get him to drink Ensure or Boost. Nutrition is totally important for recovery, and if you can't get it through the solid foods, you need to get it through the liquid supplements. This is especiallly important for patients with other health problems.
It also would be good to see if his doctors could get him a liquid form of his other medications. It's not a good thing for him to be off of them while he's recovering from the radiation. He needs to use all of his energy to recover from the cancer treatments. Any other health problems flaring up could impede his progress. All patients need to keep as healthy as possible during treatments and recovery so things go smoothly.
The lack of energy thing is totally common. I am 4 months out and just started to have energy again last week. I used to have "crash days" every other day, but now get them less and less. What really helped me improve was getting my diet back in line. I hadn't been getting enough calories (both by mouth and by PEG tube) and was told by the doctor that I had 5 weeks to gain 10 pounds. My energy started to return as I gained the weight. The deadline passed and I still am 4 pounds short, but I'm still working on it. I have to thank the inventors of Boost for getting me through all of this.
I'll keep you and your hubby in my prayers. Good luck.