Safety and efficacy of INTRABEAM intraoperative radiotherapy for invasive thymoma

Intraoperative radiotherapy (IORT) has been used to treat different residual solid tumors after tumor removal and has shown many advantages over other treatment methods. However, the use of IORT for invasive thymoma has not been reported. Therefore, in this study, we tried to determine the safety and efficacy of INTRABEAM IORT for the treatment of invasive thymoma. Among the patients admitted to our hospital from September to December 2016 who were diagnosed with invasive thymoma, 14 were selected as study subjects. With medical histories taken beforehand, 8 of these patients were diagnosed with Masaoka stage IIA and 6 with Masaoka stage IIB; furthermore, 5 of the patients were diagnosed with myasthenia gravis (MG). INTRABEAM radiation (8-10 Gy, low energy) was delivered to the postoperative tumor bed of each patient during surgery. The intra- and postoperative complications were observed and evaluated, and the improvement in symptoms was assessed. An additional 23 patients with stage II thymoma undergoing radical surgery from April to August 2016 were chosen as the control group. One month after the operation, only 1 patient in the IORT group had cough, increased levels of leucocytes and neutrophils, and pulmonary inflammation on chest computed tomography. Reactive inflammation and pleural effusion in the 2 groups were similar (P > .05). There was no significant difference between the 2 groups in the improvement of myasthenia gravis (P > .05). Postoperative chest computed tomography and routine blood examination at 3 and 12 months showed that all the patients recovered, with normal hemogram levels and no pulmonary fibrosis around the radiation field. In addition, ultrasonic cardiography and electrocardiography demonstrated no significant difference before or after surgery within the IORT group. At the end of the follow-up, all the patients were alive, no relapse or remote metastasis was observed in the IORT group, and 2 inpatients in the control group had experienced relapse at 24 and 26 months. There was a significant difference in disease-free survival between the 2 groups (P = .00). It is safe to administer low-energy INTRABEAM IORT at a dose of approximately 10 Gy in patients with stage II invasive thymoma. INTRABEAM IORT does not significantly increase operation- or radiation-related complications and has no significant effect on vital organs such as the lungs and heart. Its long-term efficacy is worth expecting.