This is a function of the field of radiation and if the IMRT mapping included areas outside of the actual node that was malignant, ie known routes of mets, and the remaining nodes in the adjacent chains. Mapping of these feilds is still a subject of discussion and finite guidlines for treament vary from institution to institution and RO. In the opinion of someone who may be unqualified to discuss this from a perspective of personal experience ( I got the full blast before the days of IMRT) if things were in the feild, I would agree with your doctors. If you wanted to get a second opinion I would ask a surgical head and neck oncologist if he felt that doing a partial, modified neck disection was in order. My guess is he is going to agree with your docs. But IMHO this is a function of what got radiated.