HI, A Relative Was Diagnosed With Prostate Cancer 2nd Stage

HI, A relative was diagnosed with prostate cancer 2nd stage five years ago, after surgery and radiation every became ok. A year after he was diagnosed with intestine cancer stage 2 had chemotheraphy and again everything was ok. then later the found a spot on his lung, had chemo again and everything went well. Just recently 15 tumors were found on his brain plus there's also undrained fluid. He was diagnosed with 4th degree cancer and will undergo radio therapy. May I know what to expect with this treatment ? Thank you