Hypofractionated Adjuvant Radiotherapy for Thymic Epithelial Tumors

Inclusion Criteria: 1. Thymic epithelial tumor, including thymoma or thymic carcinoma, confirmed by pathology. 2. Received radical thymothymectomy. 3. Masaoka-Koga stage I to III disease with an indication for postoperative radiotherapy. 4. Age \>= 18 years. 5. Karnofsky performance status \>= 70%. 6. Life expectancy \>= 1 year. 7. Sufficient bone marrow reserve, renal function, and liver function within 90 days prior to registration, defined as: white blood cell count \>= 2000/mm3; platelet count \>= 50,000/mm3; hemoglobin \>= 8 g/dL; serum creatinine \<= 2.0 mg/dL or estimated glomerular filtration rate \>= 30 mL/min; AST/ALT \<= 2.5 times the upper limit of normal. 8. Women of childbearing potential must have a negative qualitative serum or urine pregnancy test within 14 days prior to study entry. 9. Able to comply with study procedures and follow-up schedules and willing to provide study-specific informed consent. Exclusion Criteria: 1. Prior radiotherapy to the thorax. 2. Severe active comorbidities that, in the judgment of the investigator, make the patient inappropriate for study entry, interfere with safety or adverse event assessment, or limit compliance with study requirements, including: uncontrolled active infection requiring intravenous antibiotics at registration; transmural myocardial infarction \<= 6 months prior to registration; unstable angina or congestive heart failure requiring hospitalization \<= 6 months prior to registration; life-threatening uncontrolled clinically significant cardiac arrhythmias; hepatic insufficiency resulting in clinical jaundice and/or coagulation defects; chronic obstructive pulmonary disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy at registration; uncontrolled psychiatric disorder. 3. Planned receipt of another investigational treatment during radiotherapy. 4. Planned concurrent chemotherapy during radiotherapy. Prior induction or neoadjuvant chemotherapy, or planned sequential adjuvant chemotherapy after adjuvant radiotherapy, is allowed. 5. Pregnant or breastfeeding women. 6. Women of childbearing potential and sexually active male participants who are unwilling or unable to use medically acceptable contraception during radiotherapy and for 3 weeks after completing treatment.