Brachytherapy With Radiotherapy and Immunotherapy: Guided HDR Trial in Esophageal Squamous Cell Carcinoma

Inclusion Criteria: * Age of 18-85 years, with ECOG performance 0-2. * Locally-advanced esophageal squamous cell carcinoma with clinical stage III, IVA with biopsy proven. * Prior treatment with EBRT (40-50.4 Gy in 20-28 fractions) and platinum + fluoropyrimidine chemotherapy, with residual or progressive disease, and deemed inoperable or unable to undergo surgery. * No prior exposure to ICIs and had received first cycle of nivolumab after CCRT. * Biopsy proven with PD-L1 \[tumor cell (TC) ≥ 1%\] * Required at least one measurable or non-measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1. * Patients with limited stage IVB disease (e.g., non-visceral lymph node metastasis) may be enrolled if the primary tumor is locally dominant and suitable for brachytherapy, based on investigator's discretion. Exclusion Criteria: * Current or past history of severe hypersensitivity to any other antibody products. * Patients with any metastasis in the brain or meninx that is symptomatic or requires treatment. * Patients with active, known or suspected autoimmune disease * Stenosis of esophageal lumen that cannot performed brachytherapy * Involvement of tracheal mucosa or bronchial mucosa. * The distribution of the lesions of interest exceeds 10 cm range. * The patient is participating in other interventional clinical trials associated with immunotherapy. * The patient is scheduled to undergo esophagostomy.