Clinical Research Directory

Inclusion Criteria: * Age ≥18 years at the start of treatment, regardless of sex. * Histologically or cytologically confirmed esophageal squamous cell carcinoma. * Clinical stage cT2-4aN0-3M0 and received definitive radiotherapy or preoperative radiotherapy, with systemic treatment consisting of concurrent chemoradiotherapy with or without immunotherapy. * Received modern precision radiotherapy, including IMRT, VMAT, TOMO, or proton therapy, with the original radiotherapy plan, target structures, and dose distribution available for review. * Contrast-enhanced CT available before treatment for staging and target volume review; endoscopy, EUS, PET/CT, or MRI may also be used when available. * Major baseline characteristics, treatment information, and at least one efficacy or safety assessment available in the medical record; this requirement does not apply to patients who died during treatment. * Treatment occurred within the predefined study period and met the data-use conditions approved by the ethics committee. Exclusion Criteria: * Distant metastasis, malignant pleural or peritoneal effusion before treatment, or radiotherapy given with a clearly palliative intent. * Previous thoracic radiotherapy that could substantially affect current target volume design, dosimetric assessment, or outcome evaluation. * Other active malignancies that could substantially affect survival or recurrence outcomes. * Missing original radiotherapy plan or DICOM-RT data, preventing determination of the GTV-CTV longitudinal margin, regional lymph node irradiation extent, or key dosimetric parameters. * Severe missing clinical, pathological, or follow-up data preventing determination of the primary exposure or major outcomes. * Duplicate cases; only the first eligible treatment record will be included.