For a patient who has undergone preoperative chemoradiation to 50Gy for locally advanced rectal cancer followed by LAR or APR, would you treat a positive margin with radiation therapy?

No. The majority are still controlled locally even with a positive margin. The cells seen on histologic evaluation may be clonogenicly dead. After an 8-12 week interval, there is not much that can be done with more irridation anyway. Previuosly irradiated fixed bowel could be in the field. Furthermo...

This is somewhat controversial, IORT if available should be considered for very close or positive margins. If IORT is not available 10-20Gy external beam radiation to a limited volume soon after surgery. Image guidance is an issue though and discussion with surgeon should be done to delineate target...