The Combination of Hypofractionated Radiotherapy and Immunotherapy in Locally Recurrent Rectal Cancer

Inclusion Criteria:

* Patient is 18-75 years old at the time of signing the informed consent form.
* ECOG performance status 0-1.
* MRI/enhanced CT confirmed pelvic recurrence. According to RECIST 1.1, there is at least one measurable pelvic lesion.
* Distant metastasis lesions are no more than 5 and metastatic organ are no more than 3.
* No prior radiotherapy within 6 month.
* Previous system therapy. Patients Group Cohort A: participants with pelvic recurrence who have not previously been treated with first-line chemotherapy. Cohort B: Patients with disease progression or new lesions after first-line chemotherapy.
* Has an investigator determined life expectancy of at least 24 weeks.
* Demonstrate adequate organ function (bone marrow, liver, kidney and clotting function) within 7 days before the first administration without using blood products or hematopoietic stimulating factors.
* Non pregnant or lactating patients. Effective contraceptive methods should be used during the study and within 6 months of the last administration.
* Fully informed and willing to provide written informed consent for the trial.

Exclusion Criteria:

* Neutrophil \< 1.5×10\^9/L, PLT \< 100×10\^9/L (PLT \< 80×10\^9/L in patients with liver metastasis), or Hb \< 90g/L; blood transfusion within 2 weeks before enrollment is not allowed to meet the enrollment criteria.
* 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 \< 50ml / 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-hour urine protein ≥1.0g/24h.
* Uncontrolled hypertension: SBP \>140mmHg or DBP \> 90mmHg.
* The presence of gastrointestinal diseases such as gastric or duodenal active ulcers, ulcerative colitis or unresected tumours with active bleeding; or other conditions likely to cause gastrointestinal bleeding or perforation; or unhealed gastrointestinal perforation or gastrointestinal fistula after surgical treatment.
* 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 (including congestive heart failure, acute myocardial infarction, severe/unstable angina, coronary artery bypass grafting, cardiac insufficiency ≥ NYHA grade 2 and LVEF\<50%).
* Uncontrolled malignant pleural effusion, ascites, or pericardial effusion.
* History of anti-PD-1, PD-L1, PD-L2, CTLA-4 or any other specific T cell co-stimulation or checkpoint pathway targeted therapy.
* The presence of a clinically detectable second primary malignancy, or history of other malignancies within 5 years excluding adequately treated non-melanoma skin cancer, carcinoma in situ of cervix and superficial bladder tumour (non-invasive tumour, or carcinoma in situ, or T1).
* A history of liver disease including, but not limited to HBV infection or HBV DNA positive(≥1×10\^4/ml), HCV infection or HCV DNA positive(≥1×10\^3/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 3cm or the total volume is greater than 30cc.
* Clinical or radiological evidence of spinal cord compression, or tumours within 3 mm of the spinal cord on MRI.