To determine dosimetric parameters associated with osteoradionecrosis (ORN) in oropharyngeal cancer (OPC) patients in the IMRT era.

Subsequent to institutional review board approval, we identified ORN in OPC patients treated with IMRT from 2002 to 2013. 1:2 case-control matching was implemented. Mandibular dose-volume histograms (DVH) were extracted. Dosimetric parameters were compared using non-parametric stats. Recursive partitioning analysis (RPA) was done to identify DVH correlates of ORN.

68 ORN cases and 131 controls were matched. Median follow-up was 41months and median time to development of ORN was 16months. Mandibular mean dose was significantly higher in the ORN cohort (48.1 vs 43.6Gy, p<0.0001). However, the maximum dose was not statistically different. DVH bins from V35 to V73 were all significantly higher in the ORN cohort compared with controls (p<0.0006). Two DVH parameters were identified in RPA analysis, V43 and V58. The majority (81%) of ORN cases were observed with both V44≥42% and V58≥25%.

Our data demonstrate that a wide range of DVH parameters in the intermediate and high beam path were all significantly higher in ORN patients. Mandibular V44<42% and V58<25% represent reasonable DVH constraints for IMRT plan acceptability, when tumor coverage is not compromised.