Radiotherapy Target Volume Delineation in Locally Advanced Esophageal Cancer in the Immunotherapy Era

Inclusion Criteria: 1. Age 18 to 80 years, regardless of sex. 2. Histologically confirmed esophageal squamous cell carcinoma. 3. Clinical stage cT2-4aN0-3M0, or considered by a multidisciplinary team to be suitable for definitive immunotherapy combined with radiotherapy or preoperative immunotherapy combined with radiotherapy. 4. Planned to receive one of the following modern precision radiotherapy techniques: IMRT, VMAT, TOMO, proton therapy, or heavy-ion radiotherapy. 5. Contrast-enhanced CT completed before radiotherapy; endoscopy, EUS, PET/CT, or MRI is recommended when clinically appropriate to assist target volume delineation. 6. ECOG performance status of 0-2. 7. Expected survival of at least 6 months. 8. Able to understand the study and provide written informed consent. Exclusion Criteria: 1. Presence of distant metastasis or malignant pleural or peritoneal effusion. 2. Previous thoracic radiotherapy that may affect the current target volume design or dose constraints. 3. Pre-existing esophagotracheal fistula, esophagoaortic fistula, or a high risk of perforation considered unsuitable for radiotherapy. 4. Active interstitial lung disease, severe infection, or uncontrolled autoimmune disease considered unsuitable for immunotherapy. 5. Severe missing data that prevent determination of the actual CTV margin, lymph node irradiation extent, or major study outcomes. 6. Any other condition that, in the investigator's judgment, makes the patient unsuitable for participation in the study.