Dear Father's Daughter,
Sorry it takes all day for me to reply, but I work nights and that is when I spend most of my time on the computer. Wow! You sound just like my wife and I when we were told of the CC. We felt like we could spend 24 hours a day gaining knowledge and it was exhausting. Be careful not to drive yourself crazy by trying to absorb everything at once. It is easy to forget about yourself during this time, but you need to take care of you as well as help your dad.
My father in law's cancer was near the junction of the two bile ducts, the tumor was borderline between intra and extra(that was my take on the doctor's explanation). It sounds like marylloyd is more knowledgeable about the topic of radiation than I, but I will share what I do know. For most people, I believe, quantity of radiation is not of much concern. For my fil(father in law), it was of concern for this was his third primary cancer, and he had received radiation in the past(he has had stomach cancer and lymphoma starting in the 90's, which shows he was with us for a long time even with these cancers). We never experienced radiation causing nausea, only chemo which pretty much wiped him out for a couple of days after each treatment. Whatever may cause him to be nauseous can be counteracted by medicine.
As a family, we always had a positive outlook regarding CC, including my fil. I think positive thinking has healing powers-the mind can convince the body about many different things(that sounds alot better in my head than it does on the screen but I hope you get the meaning). My fil wanted to fight as long as there were still options to possibly get him better. He was sick, fatigued and sometimes nauseous, but he felt good most of the time, until the final month or two. When a doctor would tell us, "this is all we can do", we would consult with someone else and sure enough, there was something else they could do. So don't take one doctor's opinion as gold, each doctor has there own way of doing things, and some are more up to date with new medicines, treatments and clinical trials. The doctor that gave you a timeframe on your father's life is making a guess, maybe an educated one, but a guess nonetheless. My fil's was a stage IV by the time we found out, it sounds like you got a better jump on it than we did.
There are many 'natural' ways (that some people swear by) to help him through this and if he chooses not to seek medicinal treatment, he might want to try some of these(this I know very little about). As marylloyd said, good nutrition cannot be streesed enough. You want to be as healthy as possible in all aspects to better fight this.
Hang in there,