Anyone experience painful urinating after radiation?

My husband experienced extremely painful and burning bladder and urine after his 3rd proton beam radiation treatment, it started one hour after his treatment on our way home a 4 hour ride. It continued for over 4 hours, his not able to pee almost anything at times, but still pain. Today we are back for treatment 4 and are so afraid. No coffee this time before, but only had one cup in the morning and treatment was after 2:00. He also drank plenty of water. He does have an enlarged prostate, is 80, but has never had an issue, any suggestions.
Thank you