• Rahul R Parikh, Ryan Rhome, Eugen Hug, Henry Tsai, Oren Cahlon, Brian Chon, and Anuj Goenka.
• Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ. Electronic address: parikhrr@cinj.rutgers.edu.
• Clin Lung Cancer. 2016 Sep 1; 17 (5): 362-366.

BackgroundWe evaluated the dosimetric differences between proton beam therapy (PBT) and intensity modulated radiation therapy (IMRT) for resected thymoma. We simultaneously report our early clinical experience with PBT in this cohort.Patients And MethodsWe identified 4 patients with thymoma or thymic carcinoma treated at our center from 2012 to 2014 who completed adjuvant PBT to a median dose of 57.0 cobalt Gy equivalents (CGE; range, 50.4-66.6 CGE) after definitive resection. Adjuvant radiation was indicated for positive (n = 3) or close margin (n = 1). Median age was 45 (range, 32-70) years. Stages included II (n = 2), III (n = 1), and IVA (n = 1). Analogous IMRT plans were generated for each patient for comparison, and preset dosimetric endpoints were evaluated. Early toxicities were assessed according to retrospective chart review.ResultsCompared with IMRT, PBT was associated with lower mean doses to the lung (4.6 vs. 8.1 Gy; P = .02), esophagus (5.4 vs. 20.6 Gy; P = .003), and heart (6.0 vs. 10.4 Gy; P = .007). Percentages of lung, esophagus, and heart receiving radiation were consistently lower in the PBT plans over a wide range of radiation doses. There was no difference in mean breast dose (2.68 vs. 3.01 Gy; P = .37). Of the 4 patients treated with PBT, 3 patients experienced Grade 1 radiation dermatitis, and 1 patient experienced Grade 2 dermatitis, which resolved after treatment. With a median follow-up of 5.5 months, there were no additional Grade ≥ 2 acute or subacute toxicities, including radiation pneumonitis.ConclusionPBT is clinically well tolerated after surgical resection of thymoma, and is associated with a significant reduction in dose to critical structures without compromising coverage of the target volume. Prospective evaluation and longer follow-up is needed to assess clinical outcomes and late toxicities.Copyright © 2016 Elsevier Inc. All rights reserved.

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