Long-term Outcomes After Moderate Hypofractionated Proton Therapy for Centrally Located Non-small Cell Lung Cancer

Background/Aim: To investigate the outcomes of patients with centrally located non-small-cell lung cancer (NSCLC) treated with proton beam therapy (PBT) using moderate hypofractionation. Patients and Methods: Between 2006 and 2019, 34 patients with centrally located T1-T4N0M0 NSCLC who received moderate hypofractionated PBT were retrospectively reviewed. Results: The median follow-up was 50.8 months (range=5.8-100.4 months). The 3-year overall survival, progression-free survival (PFS), and local control rates were 70.4%, 55.5% and 80.5%, respectively. Grade 2 or 3 lung adverse events (AEs) after PBT were observed in five (14.7%) patients; however, grade 3 radiation pneumonitis was observed in one (2.9%) patient. Notably, no grade 4 or higher AEs were observed. Regarding the correlation between the lung dose and proximal bronchial tree maximum dose and grade 2 or higher lung AEs, a weak correlation was observed between the mean lung dose and AEs (p=0.035). Although the clinical target volume (CTV) was a risk factor for poor PFS, no significant correlation was found between the CTV and lung AEs after PBT. Conclusion: Moderate hypofractionated PBT may be a useful radiotherapy method for centrally located cT1-T4N0M0 NSCLC.