Hypofractionated Radiotherapy Plus Immunotherapy Versus Conventional Radiotherapy in Locally Recurrent Rectal Cancer

Inclusion Criteria: Patient is 18-75 years. ECOG performance status 0-1. MRI/enhanced CT confirmed pelvic recurrence. Without synchronous distant metastases. No prior radiotherapy within 6 month. No prior first-line chemotherapy. Has an investigator determined life expectancy of at least 24 weeks. Demonstrate adequate organ function. Non pregnant or lactating patients. Fully informed and willing to provide written informed consent for the trial. Exclusion Criteria: Neutrophil\< 1.5×109/L, PLT\< 100×109/L (PLT\< 80×109/L in patients with livermetastasis), or Hb\< 90 g/L. TBIL \> 1.5 ULN, or TBIL \> 2.5 ULN in patients with liver metastasis. AST or ALT \> 2.5 ULN, or ALT and/or AST \> 5 ULN in patients with liver metastasis. Cr \> 1.5 ULN, or creatinine clearance\< 50 mL/min (calculated according to Cockcroft Gault formula). APTT \> 1.5 ULN, PT \> 1.5 ULN (subject to the normal value of the clinical trial research center). Serious electrolyte abnormalities. Urinary protein ≥ 2+, or 24-h urine protein ≥1.0 g/24 h. Uncontrolled hypertension: SBP \>140 mmHg or DBP \> 90 mmHg. A history of arterial thrombosis or deep vein thrombosis within 6 months; a history of bleeding or evidence of bleeding tendency within 2 months. A history of heart disease within 6 months. Uncontrolled malignant pleural effusion, ascites, or pericardial effusion. History of checkpoint inhibitor therapy. The presence of a clinically detectable second primary malignancy, or history of other malignancies within 5 years. A history of liver disease including, but not limited to, HBV infection or HBV DNA positive (≥1×104/mL), HCV infection or HCV DNA positive (≥1×103/mL), and liver cirrhosis. Pregnant or lactating women or women who may be pregnant have a positive pregnancy test before the first medication, or the female participants themselves and their partners who were unwilling to implement strict contraception during the study period. The investigator considers that the subject is not suitable to participate in this clinical study due to any clinical or laboratory abnormalities or compliance problems. Serious mental abnormalities. The diameter of brain metastasis is greater than 3 cm or the total volume is greater than 30 cc. Clinical or radiological evidence of spinal cord compression, or tumors within 3 mm of the spinal cord on MRI.