I asked my doc the same question after one of my nodes tested positive. Why do I need radiation? Didn’t you get all the lymph nodes? The answer I was given is no. First of all, some lymph nodes are too small to be seen by the doctor in OR. Second, they can only remove the nodes that are visible and can be reached. There are some lymph nodes that are deeper in the neck. Also different people have different number of lymph nodes and in different areas. It’s not as precise a procedure as I had imagined. Research shows that if even one node is positive the chance of recurrence increases. Just my opinion however