Everyday immediately after each proton radiation treatment I headed straight for the gym to lift weights. (That prevented me from being at home and having any excuses to miss working out.)

In addition, every other day, I also either swam laps for 35-45 minutes or ran a 5K.

My change of diet included a protein/fruit smoothie every morning, and a protein bar & two energy bars every day. I think that was helpful in sustaining energy and endurance during the months of low-testosterone.

Also important was for the radiation not to overshoot the prostate. The more otherwise healthy nearby tissues and organs that get hit with unnecessary radiation, the more fatigue will set in as the body has to deal with that.