title: Adjuvant Proton Beam Therapy in the Management of Thymoma: A Dosimetric Comparison and Acute Toxicities.
abstract: We 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.
  
  
  
  We 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.
  
  
  
  Compared 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.
  
  
  
  PBT 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.
authors.affiliation: Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ. Electronic address: parikhrr@cinj.rutgers.edu.
authors.forename: Rahul R
authors.initials: RR
authors.lastname: Parikh
authors.affiliation: Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai, New York, NY.
authors.forename: Ryan
authors.initials: R
authors.lastname: Rhome
authors.affiliation: Princeton Radiation Oncology, Princeton, NJ; ProCure Proton Therapy Center, Somerset, NJ.
authors.forename: Eugen
authors.initials: E
authors.lastname: Hug
authors.affiliation: Princeton Radiation Oncology, Princeton, NJ; ProCure Proton Therapy Center, Somerset, NJ.
authors.forename: Henry
authors.initials: H
authors.lastname: Tsai
authors.affiliation: Princeton Radiation Oncology, Princeton, NJ; ProCure Proton Therapy Center, Somerset, NJ.
authors.forename: Oren
authors.initials: O
authors.lastname: Cahlon
authors.affiliation: Princeton Radiation Oncology, Princeton, NJ; ProCure Proton Therapy Center, Somerset, NJ.
authors.forename: Brian
authors.initials: B
authors.lastname: Chon
authors.affiliation: Department of Radiation Medicine, North-Shore LIJ Health Systems, New Hyde Park, NY.
authors.forename: Anuj
authors.initials: A
authors.lastname: Goenka
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D061766:Proton Therapy / Q000009:adverse effects / Q000379:methods*; D011832:Radiation Injuries / Q000453:epidemiology; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant / Q000009:adverse effects / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D013945:Thymoma / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D013953:Thymus Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D016896:Treatment Outcome
keywords: Adjuvant radiation; IMRT; Mediastinum; Proton therapy; Radiation therapy; Thymoma