Molly,
my mother had RAD before her neck dissections, and they told us it was because when she was diagnosed, her tumors were too big for surgery. She had 35 RAD treatments, to shrink the tumors, so they would be operable. Her chemo was for cancer on the tongue, and the RAD greatly reduced the tumors in the lymph nodes...they also removed other nodes, and they tested negative. I'm not certain, but I think that is the main idea of RAD pre-op.....possibly the RAD after an operation would be to get rid of any remnants?? Not sure!