GTV-CTV Longitudinal Margin

This prospective observational cohort study will evaluate different radiotherapy target volume delineation patterns in patients with locally advanced esophageal squamous cell carcinoma receiving radiotherapy combined with immunotherapy. In routine clinical practice, physicians may use different margins around the primary tumor and different approaches to regional lymph node irradiation. The study will not assign participants to a specific radiotherapy strategy. Instead, participants will receive treatment according to routine clinical practice, and the actual radiotherapy plans will be recorded and analyzed. The study will compare locoregional tumor control, recurrence patterns, survival, treatment-related toxicity, lymphocyte reduction, and completion of immunotherapy among patients receiving different target volume strategies. The main objective is to evaluate 2-year locoregional recurrence-free survival and to identify radiotherapy approaches that may achieve effective tumor control while reducing unnecessary radiation exposure and treatment-related toxicity.