Gross tumor volume margin and local control in p16‐positive oropharynx cancer patients treated with intensity modulated proton therapy

Background To determine if the extent of high‐dose gross tumor volume (GTV) to clinical target volume (CTV) expansion is associated with local control in patients with p16‐positive oropharynx cancer (p16+ OPC) treated with definitive intensity modulated proton therapy (IMPT). Methods We performed a retrospective analysis of patients with p16+ OPC treated with IMPT at a single institution between 2016 and 2021. Patients with a pre‐treatment PET–CT and restaging PET–CT within 4 months following completion of IMPT were analyzed. Results Sixty patients were included for analysis with a median follow‐up of 17 months. The median GTV to CTV expansion was 5 mm (IQR: 2 mm). Thirty‐three percent of patients (20 of 60) did not have a GTV to CTV expansion. There was one local failure within the expansion group (3%). Conclusion Excellent local control was achieved using IMPT for p16+ OPC independent of GTV expansion. IMPT with minimal target expansions represent a potential harm‐minimization technique for p16‐positive oropharynx cancer.