Immunonutrition Reduces Acute Esophagitis After Thoracic Radiotherapy in Lung Cancer

Inclusion Criteria: 1. The subject voluntarily participates in this clinical study, understands the study procedures, and is able to provide written informed consent. 2. Age ≥ 18 years. 3. Pathologically confirmed diagnosis of lung cancer, including non-small cell lung cancer and small cell lung cancer. 4. Indication for thoracic radiotherapy, with the esophagus within 1 cm of the PTV. 5. Prescription dose for the PTV: 60-70 Gy once daily (2 Gy/Fx), 45 Gy twice daily (1.5 Gy/Fx, with intervals exceeding 6 hours), or 45 Gy once daily (3 Gy/Fx). 6. Ability to orally intake food normally. 7. Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1. 8. The volume of both lungs receiving more than 20 Gy (V20) should not exceed 30% of the total lung volume. 9. Expected survival of more than 3 months. 10. Laboratory test results during the screening period: Complete blood count: ANC ≥ 1.5 × 10\^9/L; PLT ≥ 80 × 10\^9/L; Hb ≥ 90 g/L. Blood biochemistry: TBIL ≤ 1.5 × ULN; ALT and AST ≤ 2 × ULN; BUN and Cr ≤ 1.5 × ULN, with creatinine clearance ≥ 50 mL/min (calculated using the Cockcroft-Gault formula). 11. Female subjects of childbearing potential, male subjects, and partners of male subjects agree to use reliable contraceptive methods during the study period (such as abstinence, sterilization, oral contraceptives, or other contraceptive measures). Exclusion Criteria: 1. Previous history of thoracic radiotherapy. 2. Suspected or confirmed tumor invasion of the esophagus. 3. Patients with other primary tumors. 4. History of esophageal cancer, gastric cancer, or prior esophageal surgery. 5. Concurrent active reflux esophagitis. 6. Current regular use of immunonutrition (e.g., Oral Impact®). 7. Patients with severe cardiovascular or cerebrovascular diseases, or comorbidities such as liver or kidney diseases. 8. Female subjects who are pregnant, breastfeeding, or planning to become pregnant during the study period. 9. Concurrent active autoimmune diseases requiring treatment. 10. Known history of human immunodeficiency virus (HIV) positivity or acquired immunodeficiency syndrome (AIDS). 11. Any medical (e.g., pulmonary, metabolic, endocrine, or neurological diseases, congenital disorders, etc.), psychiatric, or social condition that, in the investigator's judgment, may interfere with the subject's rights, safety, health, or ability to provide informed consent, cooperate and participate in the study, or interfere with the evaluation of the study drug, interpretation of patient safety, or study results.