Nelie,
For what it's worth, I had radiation focused mainly on the right side of my mouth and neck. The radiation oncologist at Mass General said that given the location of my tumor (on the very right side of my mouth between my teeth and gum) the radiation fields she was using would do the job. I pushed the radiation oncologist about this and she was convinced that her approach would be successful. After reading posts on the board, I wished in retrospect that I had both sides radiated. Time will tell, I'm 10 months post-radiation.
You might also want to ask your radiation oncologist about the possibility of combining Erbitux (a monoclonal antibody treatment, not a chemo drug) with radiation. A recent Phase III trial indicated that this is a more successful approach than radiation alone and it might not interfere with the healing from your breast cancer surgery. Best wishes for a successful treatment. - Sheldon