Comparative Outcomes After Definitive Chemoradiotherapy Using Proton Beam Therapy Versus Intensity Modulated Radiation Therapy for Esophageal Cancer: A Retrospective, Single-Institutional Analysis

Abstract

Purpose: To compare clinical outcomes between proton beam therapy (PBT) and intensity modulated radiation therapy (IMRT) in patients with esophageal cancer (EC) treated with definitive chemoradiotherapy (CRT).

Methods and materials: From 2007 through 2014, 343 EC patients who received definitive CRT with either PBT (n=132) or IMRT (n=211) were retrospectively analyzed. Survival, recurrence, and treatment toxicity were compared between groups. A Cox proportional hazards regression model was performed to test the association between patient/treatment variables and survival.

Results: Patient/treatment variables were overall well balanced, except for age and race. Compared with IMRT, PBT had significantly better overall survival (OS; P=.011), progression-free survival (PFS; P=.001), distant metastasis-free survival (DMFS; P=.031), as well as marginally better locoregional failure-free survival (LRFFS; P=.075). No significant differences in rates of treatment-related toxicities were observed between groups. On multivariate analysis, IMRT had worse OS (hazard ratio [HR] 1.454; P=.01), PFS (HR 1.562; P=.001), and LRFFS (HR 1.461; P=.041) than PBT. Subgroup analysis by clinical stage revealed considerably higher 5-year OS (34.6% vs 25.0%, P=.038) and PFS rates (33.5% vs 13.2%, P=.005) in the PBT group for patients with stage III disease. However, no significant intergroup differences in survival were identified for stage I/II patients.

Conclusions: Compared with IMRT, PBT might be associated with improved OS, PFS, and LRFFS, especially in EC patients with locally advanced disease. These results need confirmation by prospective studies.