Submandibular gland sparing when irradiating neck level IB in the treatment of oral squamous cell carcinoma.

Patients with oral squamous cell carcinoma (OSqCCA) frequently require postoperative radiation (PORT), which may include contralateral level IB within the clinical target volume (CTV). The submandibular gland (SMG) is typically included within the level IB CTV; however, the SMG does not contain lymph nodes or lymphatic vessels. We hypothesized that level IB could be adequately irradiated while sparing the SMG to reduce xerostomia. Twelve patients with OSqCCA receiving PORT, which included the contralateral level IB within the planning target volume (PTV), were retrospectively reviewed and replanned using volumetric modulated arc therapy. CTV contouring, including contralateral level IB, was in accordance with the consensus contouring atlas but excluded the SMG. The contralateral neck PTVs were planned to 54 Gray (Gy) (PTV54). Dose requirements were per Radiation Therapy Oncology Group-1008: PTV54 D95% >54 Gy, with an allowable variation of >48.6 Gy. The dose constraint for the SMG was mean dose ≤39 Gy based on published dose-effect data for the SMGs. Mean SMG and PTV54 doses were 38.5 Gy and 56.3 Gy, respectively. Median PTV54 D95% was 53.0 Gy (range 52.5 to 54.6 Gy), with all cases meeting our allowable coverage goal. When assessing the portion of the PTV associated with level IB only (PTV_IB), mean PTV_IB dose was 54.4 Gy and median PTV_IB D95% was 43.3 Gy (range 42.5 to 52.2). Median D95% to CTV_IB was 50.2 Gy. SMG sparing resulted in 10% to 20% underdosing of the part of the PTV corresponding to level IB, as a portion of the PTV lies within the SMG. The SMG can be spared to a mean dose ≤39 Gy with slight underdosing of the surrounding PTV where the PTV overlaps with the SMG. Clinical trials evaluating SMG sparing are warranted.

Predictors of severe long-term toxicity after re-irradiation for head and neck cancer.

OBJECTIVE: To identify predictive factors of severe long-term toxicity after re-irradiation of recurrent/persistent or second-primary head and neck cancer. METHODS: Outcomes and treatment plans of patients who underwent modern IMRT based re-irradiation to the head and neck from 2008-2015 were reviewed. Co-variables including demographic, clinical and oncologic factors, as well as interval to re-irradiation and re-irradiated planning tumor volume (PTV) were analyzed as predictors of developing severe (CTCAE grade⩾3) long-term toxicity with death as a competing risk. RESULTS: A total of 66 patients who met inclusion criteria were eligible for analysis. A median re-irradiation dose of 70Gy was delivered at a median of 37.5months after initial radiotherapy. Re-irradiation followed surgical resection in 25 (38%) patients, and concurrent chemotherapy was delivered to 41 (62%) patients. Median follow-up after re-irradiation was 23months and median overall survival was 22months (predicted 2year overall survival 49%). Of the 60 patients who survived longer than 3months after re-irradiation, 16 (25%) patients experienced severe long-term toxicity, with the majority (12 of 16) being feeding tube -dependent dysphagia. In multivariable analysis, shorter intervals to re-irradiation (<20months) and larger re-irradiated PTVs (>100cm(3)) were independent predictors of developing severe long-term toxicity. Patients with longer disease-free intervals and smaller PTVs had a 94% probability of being free of severe toxicity at two years. CONCLUSION: Selection of patients with longer re-irradiation intervals and requiring smaller re-irradiated PTVs can independently predict avoidance of severe long-term toxicity.