Sequential Tegafur-gimeracil-oteracil Potassium Capsule (s-1) and Serplulimab Following Concurrent Chemoradiotherapy for Esophageal Squamous Cell Carcinoma

Serplulimab will be administered as a fixed dose of 300 mg via intravenous infusion every three weeks, continuing for up to 12 months or until disease progression, unacceptable toxicity, or withdrawal of consent

S1 will be administered at a dose of 60 mg/m2 per day, taken orally in two divided doses on day 1 concurrent with radiotherapy, repeated every 28 days; and from day 1 to day 14 of each 21-day cycle, for up to 12 months or until disease progression, unacceptable toxicity, or withdrawal of consent

Radiotherapy will be delivered as a total dose of 50.4 Gy in 28 fractions over six weeks using techniques such as IGRT, IMRT, VMAT, or TOMO, targeting the primary tumor and associated lymph nodes

Cisplatin will be administered at a dose of 75 mg/m\^2 on day 1 concurrent with radiotherapy, repeated every 28 days