First Clinical Report of Proton Beam Therapy for Post-Operative Radiotherapy for Non-Small Cell Lung Cancer

Abstract Background and Purpose The characteristic Bragg peak of proton beam therapy (PBT) allows for sparing normal tissues beyond the tumor volume that may allow for decreased toxicities associated with PORT. Here we report the first institutional experience with proton therapy for PORT in NSCLC patients and assess early toxicities and outcomes. Materials and Methods We identified 61 consecutive patients treated from 2011-2014 that underwent PORT for locally-advanced NSCLC for positive microscopic margins and/or positive N2 lymph nodes (stage III), with 27 patients receiving PBT and 34 receiving intensity modulated radiation therapy (IMRT). Results Median follow-up time was 23.1 months for PBT (2.3-42 months) and 27.9 months for IMRT (0.5-87.4 months). The median radiation dose was 50.4 Gy for PBT (50.4-66.6 Gy) and 54 Gy for IMRT (50.0-72.0 Gy). Grade 3 radiation esophagitis was observed in 1 and 4 patients in the PBT and IMRT groups, respectively. Grade 3 radiation pneumonitis was observed in 1 patient in each cohort. Dosimetric analysis revealed a significant decrease in the V5 and mean lung dose (p=0.001 and p=0.045, respectively). One-year median overall survival and local recurrence-free survival were 85.2% and 82.4% (95% CI 72.8-99.7% and 70.5-96.2%, p=0.648) and 92.3% and 93.3% (82.5-100%, 84.8-100%, p=0.816) for PBT and IMRT cohorts, respectively. Conclusions Post-operative PBT in NSCLC is well-tolerated and has similar excellent short-term outcomes when compared with IMRT. Longer follow-up is necessary to determine if PBT has a meaningful improvement over IMRT for PORT.