As I have said many times before, get yourself to a good physical therapist. Besides handling the problems that occur post neck dissection with arm weakness and massaging the scar to keep it from tightening up, they also handle post radiation problems from the accumulation of fluid under the chin. It may not go away altogether, but with proper massage, it should go down considerably, but will take a while. I think mine took a year.

Take care,
Eileen