When I had treatment there were several folks in their 70's having the same IMRT for basically Head & Neck CA. I don't know how they did after treatment as I lost contact with them when mine was completed. It is a very tough treatment and there are definitely side effects. How you fare throughout depends as much on your mental conviction to complete the treatment and not let it break you as is does on your physical condition. Only your father can know if he thinks he can handle it, but I'll say this, I think not having it will be worse. SCC usually travels a well defined path. It's looking to metastasize to your lymphatic system where it can travel to anywhere. It usually likes to setup shop in your lungs. It can also wind up in your bones, pancreas, liver, etc... No matter how you slice it, it's not good, it's deadly, and yes it will be painful. Show your father this message board and all of the threads in this section and in the root of the head & neck section. It might give him hope and the courage to face this terrible thing head on.
Good Luck!
Joe