ESTRO 2022 - Abstract Book

S432

Abstract book

ESTRO 2022

Results We observed 41 cases of ORN of the mandible (crude incidence 18.1%, 39 within 5 years), with 13 mandibular fractures (31.7%) and 15 patients with orocutaneous fistulas (36.6%). 92.7% of patients were symptomatic or required treatment (CTCAE grade ≥ 2). The Notani score (based on panoramic radiograph), was available for 35 patients (87.8%), with N=18 Grade 3, N=10 Grade 2 and N=7 Grade 1. The estimated cumulative incidence was 8.4% (SE 1.8) at 1 year, 15.9% (SE 2.5) at 3 years, and 19.8% (SE 3.0) at 5 years (Figure 1). Univariable analysis (Table 1) showed that being an active smoker at diagnosis, N-stage, any mandible resection as primary surgery, fibula reconstruction of the mandible and tumor location at the floor of mouth, were significantly associated with increased ORN risk. Looking at dosimetric factors, we found that the Dmean of the mandible was higher in patients with ORN (mean 41.1 Gy) than in patients without ORN (35.6 Gy). This was similar for the DMax (69.4 Gy vs 65.7 Gy) and V60 (37.9% vs 22.9%). Multivariable analysis (HR, 95% CI) showed that smoking at diagnosis (2.17, 1.12-4.22) and V60 (1.03, 1.01-1.04) remained significant risk factors.

Conclusion Patients treated with PORT for OCC are at high risk for ORN, with a 5-year cumulative incidence of 19.8%. Smoking at diagnosis significantly increases the risk, with a 2.18 times higher chance of developing ORN. We also found a strong relation with mandibular RT dose. We found that even small changes in treatment planning can decrease the risk of ORN, as a 1% increase of V60 leads to a patient being 3% more likely to develop ORN.

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