What adjuvant therapy would you recommend for a T3N0, grade 3, undifferentiated sarcoma of the mandible with positive margins that is not amenable to re-resection?  

From a radiation standpoint, I would offer adjuvant radiation therapy. Given positive margin, would image to make sure no gross disease. If microscopic positive margin, I would go to 66-70 Gy.

Not much in the mandible is unresectable. I would get the patient a second surgical opinion with an experienced ENT surgical oncologist. Regardless of use of RT, R0 margins are necessary for optimal local control in STS so would want to evaluate for any possibility of re-resection. (A nuance to this...