Thymoma is a common tumor in adult mediastinum and its incidence accounts for 10-20% of mediastinal tumors, mostly in the anterior mediastinum, with the same incidence in men and women, usually most common at the age of 40-50. Pathology: Most thymomas are in the shape of substantial nodules with gray or grayish-yellow surface. They are generally classified clinically as benign thymomas (non-invasive thymomas) and malignant thymomas (infiltrative thymomas). Thymoma with intact envelope and clear boundary with surrounding tissues is called benign thymoma; thymoma with incomplete or no envelope and infiltrative growth, invading the envelope or surrounding adipose tissue and organ tissue outside the envelope is called malignant thymoma. Based on the cellular composition of the tumor tissue, thymoma is divided into four types: lymphocyte-dominant, epithelial cell-dominant, mixed lymphoepithelial cell, and spindle cell type. Most of the malignant thymomas belong to the epithelial cell type. Local infiltration and lymphatic metastasis are the main modes of spread of thymoma, and invasion of important mediastinal organs is the main cause of death. Hematogenous metastasis is rare. Most thymomas occur in adults, usually between 40-50 years old. Early stage usually has no special symptoms, but as the tumor enlarges and compresses the bronchus and laryngeal nerve, or the tumor extrapolates, cough, shortness of breath, chest pain and hoarseness may appear. In late stage, cervical lymph node enlargement, superior vena cava compression syndrome and pleural effusion may occur. About 1/3 of patients can be complicated by myasthenia gravis and poor hemoglobinopoiesis. Some patients are diagnosed with thymoma on chest X-ray during routine physical examination. The diagnosis of thymoma is mainly based on chest X-ray, which can reveal a mass on one side of the anterior mediastinal region with a wide variation in mass morphology, but most of the masses are mildly lobulated. Of course, CT (MRI) examination has a higher rate of positive diagnosis and can accurately determine the location, scope and relationship between the tumor and the surrounding tissue structure. For patients who cannot undergo open thoracotomy, percutaneous needle aspiration biopsy before treatment is necessary, especially for tumors with extensive anterior mediastinal lesions, which should be differentiated from lymphoma or germ cell tumors. Clinical staging (Verley’s recommended staging in 1985) Stage According to stage I. The pericardium is intact, no infiltration, and complete resection. Ⅰa No adhesion with surrounding area. Ⅰb Fibrous adhesions with mediastinal structures. Stage II Partial infiltration, i.e. peri-peripheral growth into the mediastinal adipose tissue or adjacent pleura or pericardium Ⅱa Complete resection Ⅱb Incomplete resection with local tumor remnants. Stage III Massive infiltrative tumor Ⅲa Infiltrative growth into surrounding tissues or/and intrathoracic implantation (pericardium, pleura). IIIb Lymphatic or hematogenous metastasis. (1) Surgery is the first choice for thymoma treatment, with complete resection or removal of as many tumors as possible. (2) Radical radiotherapy is required for postoperative invasive thymoma (even for stage I cases with complete radical resection). (3) For stage I non-invasive thymoma, postoperative radiotherapy is not necessary after complete resection, but should be reviewed regularly, and once recurrence is detected, radical radiotherapy should be performed after the second surgery. (4) For advanced thymoma (stage III and IV), radiotherapy or/and chemotherapy should be actively given as long as the patient’s condition allows. Radiotherapy indications: a. Postoperative thymoma with infiltrative growth; b. Patients whose thymoma is not completely resected, patients with biopsy resection only and patients with advanced stage; c. Preoperative radiotherapy for partial thymoma; d. Treatment of recurrent thymoma. 2.Radiation source: Generally, 60Co-r rays or high-energy X-rays can be used as the radiation source. 3.Radiotherapy range: including 1-2cm of the outer edge of the tumor bed. if there is pericardial effusion, the whole mediastinum should be considered and whole pericardium radiotherapy should be given. after DT30-35Gy, the field should be shrunk in time to prevent the occurrence of radiation pneumonia and the local tumor bed should be increased. Radiation dose: 50Gy/5 weeks for lymphocyte-dominant type, 60-70Gy/6-7 weeks for other types, 40-50Gy/4-5 weeks for infiltrating thymoma with complete surgical resection. 5. Radiation field design: The range of radiation field, the focus of dose distribution, the protection of important organs such as spinal cord (controlled below 40Gy) should be determined based on CT (MRI) and surgery and pathology. Generally, we often use the previous posterior field to penetrate the treatment, and then change the two anterior oblique field plus wedge plate and a posterior median field and other central irradiation, and pay attention to the matching of each field dose, and generally do not do double supraclavicular area prophylactic radiotherapy. Treatment of thymoma with myasthenia gravis: Myasthenia gravis mainly refers to the increase of weakness of the muscles innervated by the medulla oblongata and respiratory muscles, resulting in severe difficulty in breathing or even respiratory muscle paralysis. Thymoma combined with myasthenia gravis should be handled with special care, whether surgery or radiotherapy. Before treatment, anticholinesterase drugs such as neostigmine 60mg orally or neostigmine 0.5mg intramuscularly 3-4 times/day should be given to control the symptoms of myasthenia gravis. If sweating, lacrimation, abdominal pain, diarrhea and other symptoms of sympathetic excitation occur during the treatment period, appropriate amount of atropine (0.15-0.3mg/dose) can be used to control the symptoms. During and after treatment, the myasthenia performance should be closely observed, and even if the symptoms disappear, the dose should be gradually reduced and the oral medication maintained for a period of time. In case of myasthenia gravis, the dose should be gradually increased from a small dose of 1Gy to 1.5-2Gy/time from the beginning of radiotherapy. A single high-dose irradiation is not advisable.