Proton therapy posterior beam approach with pencil beam scanning for esophageal cancer : Clinical outcome, dosimetry, and feasibility

The aim of this study is to present the dosimetry, feasibility, and preliminary clinical results of a novel pencil beam scanning (PBS) posterior beam technique of proton treatment for esophageal cancer in the setting of trimodality therapy. From February 2014 to June 2015, 13 patients with locally advanced esophageal cancer (T3-4N0-2M0; 11 adenocarcinoma, 2 squamous cell carcinoma) were treated with trimodality therapy (neoadjuvant chemoradiation followed by esophagectomy). Eight patients were treated with uniform scanning (US) and 5 patients were treated with a single posterior–anterior (PA) beam PBS technique with volumetric rescanning for motion mitigation. Comparison planning with PBS was performed using three plans: AP/PA beam arrangement; PA plus left posterior oblique (LPO) beams, and a single PA beam. Patient outcomes, including pathologic response and toxicity, were evaluated. All 13 patients completed chemoradiation to 50.4 Gy (relative biological effectiveness, RBE) and 12 patients underwent surgery. All 12 surgical patients had an R0 resection and pathologic complete response was seen in 25 %. Compared with AP/PA plans, PA plans have a lower mean heart (14.10 vs. 24.49 Gy, P < 0.01), mean stomach (22.95 vs. 31.33 Gy, P = 0.038), and mean liver dose (3.79 vs. 5.75 Gy, P = 0.004). Compared to the PA/LPO plan, the PA plan reduced the lung dose: mean lung dose (4.96 vs. 7.15 Gy, P = 0.020) and percentage volume of lung receiving 20 Gy (V20; 10 vs. 17 %, P < 0.01). Proton therapy with a single PA beam PBS technique for preoperative treatment of esophageal cancer appears safe and feasible.