Multicenter Phase III Randomized Controlled Clinical Trial of Proton Radiotherapy versus Photon Radiotherapy with Concurrent Chemotherapy Followed by Immunotherapy Consolidation for Locally Advanced Esophageal Squamous Cell Carcinoma

INTERVENTION: treatment group:Proton Radiotherapy with Concurrent Chemotherapy Followed by Immunotherapy Consolidation;Control group:Photon Radiotherapy with Concurrent Chemotherapy Followed by Immunotherapy Consolidation; CONDITION: Esophageal Squamous Cell Carcinoma PRIMARY OUTCOME: Overall survival (OS); SECONDARY OUTCOME: Incidence of grade =2 pneumonia;TRAEs;Various quality‐of‐life scales;Overall survival time without cancer;Cancer‐specific overall survival time;Progression‐free survival; INCLUSION CRITERIA: 1. Sign the informed consent; 2. 18‐80 years old, male and female; 3. Esophageal squamous cell carcinoma confirmed by cytology or histology; 4. Stage II‐ (isolated supraclavicular lymph node metastasis) IVB by imaging evaluation; 5. Patients were evaluated as unresectable by MDT, or patients refused surgery, or patients were evaluated as unable to tolerate surgery due to medical reasons; 6. ECOG: 0‐1; 7. Expected survival time >= 12 weeks; 8. Adequate organ function: (1) Hematologic function: White blood cell count (WBC) >= 3.5×10^9/L, absolute neutrophil count (ANC) >= 1.8×10^9/L, platelet count >= 75×10^9/L, hemoglobin >= 10 g/dL; (2) Adequate liver function: ALT and AST <= 1.5× upper limit of normal (ULN), bilirubin <= 1.5× ULN; (3) Adequate kidney function: In adults, endogenous creatinine clearance >= 80 mL/min or serum creatinine (SCR) <= ULN, BUN <= ULN; and urine protein < 2. For patients with baseline urine protein >= 2, a 24‐