Patterns of Failure Following Postoperative Radiation Therapy Based on "Tumor Bed With Margin" for Stage II to IV Type C Thymic Epithelial Tumor.

<bold>Purpose: </bold>The study purpose was to report failure patterns in Masaoka-Koga stage II to IV type C thymic epithelial tumor (TET) after postoperative radiation therapy (PORT) and to evaluate the suitability of PORT target volume confined to the "tumor bed only with margin."<bold>Methods and Materials: </bold>A retrospective review of 53 patients with stage II to IV type C TET was performed. The clinical outcomes, failure patterns in relation to PORT target volume, and prognostic factors were analyzed.<bold>Results: </bold>During a median follow-up period of 69 months, 14 deaths and 25 recurrences were observed. The 5-year rates of overall survival, disease-specific survival, and freedom from recurrence were 81.0%, 91.5%, and 49.7%, respectively. The failure patterns in relation to PORT target volume were in-field failure in 2 patients (3.8%), marginal in 2 (3.8%), and out of field in 23 (43.4%), respectively. The most common failure site was the pleura (12 patients), followed by the lung parenchyma (8 patients). Relapse involving the regional lymph nodes was observed in 6 patients, of whom 4 had synchronous distant failure and only 2 had isolated ipsilateral supraclavicular lymph node failure.<bold>Conclusions: </bold>The policy of PORT target volume confined to only the tumor bed seems reasonable in treating patients with stage II to IV type C TET. The development of a more effective systemic therapy regimen is warranted. [ABSTRACT FROM AUTHOR]