Table 2.

Cohort at risk (531/715 patients with > 60 Gy to the mandible bone; no ORN in bones exposed to < 60 Gy)

	Definitive IMRT	Postoperative IMRT	ORN events (N = 36)
OCC, > 60 Gy to the mandible	1/52 (2 %)	18/106 (17 %)	19/158 (12 %)
ORN G1	0	0	0
ORN G2	0	0	0
ORN G2–3	0	15	15
ORN G3	0	0	0
ORN G4	1a	3a	4
MC, > 60 Gy to the mandible	16/227 (7 %)	0/74 (0 %)	16/301 (5 %)
ORN G1	2	0	2
ORN G2	4	0	4
ORN G2–3	6	0	6
ORN G3	4	0	4
SGT, > 60 Gy to the mandible
ORN G2	0/3	1/69 (1 %)	1/72 (1 %)

^aFour of the eight postintervention osteoradionecrosis (ORN) cases observed in our cohort developed grade 4 ORN.

OCC oral cavity cancer, MC mesopharyngeal cancer, SGT salivary gland tumor.