My surgeon told me right at the beginning, on giving me my diagnosis, that I'd have the op, the chemo and the radio.
I questioned him about the radio and his reply was, well I don't want you not to have radio and then come back with metastases in a year or two's time. He said the radio was a belt and braces scenario, to make as sure as we could, that any stray cancer cells would be wiped out and make recurrence LESS likely. Note he didn't say UNlikely, just less likely so. Take whatever comfort you can from that because there really are NO guarantees with this as with everything else in life.