So sorry to hear brother. Be prepared for not only radiation side effects, but also those of low test... fatigue, weakness, mood swings, loss of muscle and gain of fat. I'm a big fan of sublingual B vitamins (taken in the am) for energy and appetite stim. Can be found anywhere on the cheap. Your gut destroys most B vitamins, so under the tongue administration is key, and has been shown to be almost an effective as injections, without the insomnia sides. Coffee and tea, besides energy boost, also mobilize fat and have antioxidants. Also watch your diet, especially sugar, alcohol and processed foods (basically all the fun stuff), you will notice a huge difference in the way you feel and heal.
Thoughts are with you.