Intensity Modulated Radiation Therapy for Pleural Recurrence of Thymoma: A Prospective Phase 2 Study

Purpose This study aimed to evaluate the efficacy and safety of intensity modulated radiation therapy (IMRT) for pleural recurrence of thymoma that was not suitable for surgery and had progressed after chemotherapy. Materials and Methods From February 2012, consecutive patients with pleural recurrence of thymoma were prospectively enrolled. Due to dose restrictions to normal tissue (lung, liver, and kidney), 3 different levels of radiation doses (30 Gy, 40 Gy, and 50 Gy) were prescribed for pleural lesions of different sizes and locations, with a daily fraction dose of 2 Gy. The objective response rate, local control time (LCT), overall survival time, and toxicity were recorded, respectively. Results By August 2016, 31 patients had completed the IMRT treatment. There were 21 male and 10 female patients, with a median age of 49 (range, 22-70) years. B3 thymoma was the major (62%) tumor subtype observed. During the median follow-up of 48 (24-70) months, the objective response rate was 97%, and the median LCT was 49 (95% confidence interval, 40.4-58.1) months. However, 29 (93.5%) patients developed out-of-field recurrence, among whom 10 (32%; 30 Gy, n = 7; 40 Gy, n = 3) developed both out-of-field and in-field recurrence. The median progression-free survival was 19 months, and no in-field recurrence occurred in the 50 Gy group. Moreover, a higher dose was related to a longer LCT. No toxicities higher than a grade 4 occurred after IMRT within the normal-tissue dose limitation. The 5-year overall survival of the patients was 81%. Conclusions IMRT for pleural recurrence may act as an alternative treatment when surgery is not feasible, with a higher dose resulting in a longer LCT. In this study, out-of-field recurrence was considerably common, but repeated IMRT for new recurrence should be cautiously carried out due to the high risk of radiation-induced pneumonitis.