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.