Painful Radiation??

My dad has esophageal cancer that has bone met. and also in his brain. They started radiation this week on his head and shoulder but although he was given plenty of pain meds prior, he made them stop the radiation on the 2nd treatment due to the extreme pain. He does have a completely torn rotary cuff in that shoulder, but is this normal?? I hate seeing him in pain, but he NEEDS this treatment to possibly slow the very aggressive growth and chemo. nor surgery is an option. Has anyone else had these problems with radiation and do you have any suggestions????