Laura,
I just went through the hemiglossectomy and modified neck dissection, and faced the same post-op dilemma you are facing. I went through this site and other internet resources like a two year old through a bowl of cheerios, and because my margins were clear, opted not to radiate. If my margins had not been clear, or if I had perineural invasion, I would have radiated (I was a day away from getting my mask fitted when I made my final decision, as it is!)
My husband of 35 years put it in perspective for me, making my decision a lot easier..
"If it was me", he said, "what would you have me do?"
When I changed focus, it cleared my decision-making process enough that I could see through the wall of "facts" I had build around my disease.

May your decision be the best one for you,
Andrea