Even if the surgery has been adequate still there are chances of disease coming back , the resin is that surgery eradicates tumour that we can see by our own eyes but there is a chance that microscopic disease which is not seen by the eye or CT or pet may be left and that may return in future. I am sure your doctor has given you the right opinion. If any doubt do discuss with your doctor in person that's the best way to eradicate doubts coz online discussion and Google will only increase your confusion. You can also see the NCCN guidelines which are followed all over the world. All oncologists follow NCCN guidelines which is the right thing to do.

As your doctor told correct only. Surgery remove the macroscopic disease and radiotherapy will kill microscopic  cancer cell leading to recurrence in the future

Please attact scanning reports and postop biopsy report to comment up on...