Purpose: To analyze risk factors and the dose-effect relationship for osteoradionecrosis (ORN) of the mandible after radiotherapy of oral and oropharyngeal cancers.
Materials and methods: One-hundred ninety-eight patients with oral (45%) and oropharyngeal cancer (55%) who had received external radiotherapy between 1990 and 2000 were retrospectively reviewed. All patients had a dental evaluation before radiotherapy. The median radiation dose was 60 Gy (range, 16-75 Gy), and the median biologically effective dose for late effects (BED(late)) in bone was 114 Gy(2) (range, 30-167 Gy(2)).
Results: The frequency of ORN was 13 patients (6.6%). Among patients with mandibular surgery, eight had ORN at the surgical site. Among patients without mandibular surgery, five patients had ORN on the molar area of the mandible. The median time to ORN was 22 months (range, 1-69 months). Univariate analysis revealed that mandibular surgery and Co-60 were significant risk factors for ORN (p = 0.01 and 0.04, respectively). In multivariate analysis, mandibular surgery was the most important factor (p = 0.001). High radiation doses over BED 102.6 Gy(2) (conventional dose of 54 Gy at 1.8 Gy/fraction) were also a significant factor for ORN (p = 0.008) and showed a positive dose-effect relationship in logistic regression (p = 0.04) for patients who had undergone mandibular surgery.
Conclusions: Mandibular surgery was the most significant risk factor for ORN of mandible in oral and oropharyngeal cancers patients. A BED of 102.6 Gy(2) or higher to the mandible also significantly increases the risk of ORN.