To identify predictive factors of severe long-term toxicity after re-irradiation of recurrent/persistent or second-primary head and neck cancer.

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.

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.

Selection of patients with longer re-irradiation intervals and requiring smaller re-irradiated PTVs can independently predict avoidance of severe long-term toxicity.