I went on a vacation at about a month out and it was the best thing ever (getting away from hospitals and doctors and cancer was much needed at that time), but I recovered from my treatments really fast. Also, you may want to take into consideration that he is going to have to stay out of the sun for the most part because of his radiation. But walking on the beach in the mornings and evenings in Florida is always nice! I would just say that if you do plan a vacation to be flexible just in case things aren't progressing very fast in the healing department or be ready to have a relaxing weekend just hanging out and not doing too much.