Abstract
We performed preoperative proton beam therapy for locally advanced thymoma and subsequently achieved complete resection. The patient was 31-year old woman, in whom chest computed tomography revealed a huge mass at the left anterior mediastinum. We diagnosed locally advanced type B3 thymoma. Because of the potential for complications to the lung and heart, definitive photon radiation therapy would have been difficult to administer. Therefore, we performed proton beam therapy, which could be administered within dose limitations. After proton beam therapy, the huge tumor had remarkably decreased in size. We were thereby able to achieve complete resection. As of 24 months after surgery, the patient has not developed any severe adverse events associated with proton beam therapy. Our experience suggests that preoperative proton beam therapy may be an effective modality for reducing tumor size, facilitating complete resection, and preventing toxicity of radiation therapy.