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The role of postoperative adjuvant radiation therapy (PORT) remains controversial. The purpose of this study was to evaluate outcomes and toxicities of PORT in a series of patients with thymoma or thymic carcinoma.

We retrospectively analysed 27 consecutive patients (17 thymomas, 8 thymic carcinomas) who underwent surgery with a curative intent and PORT to the mediastinal surgical bed and microscopic/macroscopic disease, if present, from 2006 to 2020 at our institution. Eight patients received neo-adjuvant chemotherapy prior to surgery.  Surgical margins status was reported as follow: R0 resection (microscopic negative margin) was achieved in 14 patients, R1 (microscopic positive margin) in 11 patients and R2 (macroscopic positive margin) in 2 patients. According to Masaoka-Koga staging system 4, 6, 13 and 4 patients were stage I, II, III and IV of disease, respectively. Acute toxicities were graded according to the RTOG/EORTC scor­ing system and late toxicities where scored according to the SOMA (symptoms, objective, management, analytic) scoring system. The Kaplan Meier method was used to assess overall survival (OS), relapse-free survival (RFS) and metastases-free survival (MFS). Sub-group analysis was performed stratifying patients with R0 vs R1-2 resection margins, patients staged I-II vs III-IV stages and patients with A-AB-B1 vs B2-B3-0 histologies.

PORT was administered with 3-dimesional conformal radiotherapy in 23 patients while 4 patients were treated with intensity-modulated radiotherapy. The median planning target volume (PTV) was 250cc (range 60-610). Median dose was 54 Gy delivered using conventional fractionation (2 Gy daily). Median follow-up was 54 months. OS at 1- and 5-years was 96.3% and 89%. One- and 5-year RFS was 100% and 83%. MFS at 1- and 5-years was 92% and 67%. Patients with stages III-IV had worst 5-yers OS and MFS compared to stages III-IV, 83 vs 100% (CI 95%: 1.16-2.06; p 0.03) and 45 vs 100% (CI 95%: 1.42-2.8; p 0.01). WHO histologies B2-B3-0 showed worst 5-years OS and MFS compared to A-AB-B1 group, 82.6 vs 100% (CI 95%: 1.27-2.2; p 0.02) and 46.6 vs 100% (CI 95%: 1.2-2.6; p 0.02) . No acute nor late G3-4 toxicities were observed.

PORT in patients with thymic malignancies achieved good local control and a safe toxicity profile. Patients with III and IV Masaoka stage and WHO B2-B3-0 histology had significant worst OS and MFS.