The study is a prospective, single-center, single-arm, phase II clinical trial. Patients with pelvic recurrent rectal cancer aged from 18 to 75 years, Eastern Cooperative Oncology Group performance status of 0-1, will receive 45-50Gy/25Fx irradiation or 30Gy/15Fx reirradiation (history of pelvic radiation). PD-1 inhibitor (Toripalimab) was used throughout the course of induction chemotherapy (before radiation), concurrent chemoradiation and consolidation chemotherapy (after radiation); radical resection was followed by well-experienced surgeons .

The primary endpoint was pathological complete response (pCR) rate. Secondary endpoints were R0 resection rate, 3-year progression-free survival, overall survival, pathological tumor regression grade, operation characteristics and incidence of major surgical complications.

Inclusion Criteria:

1. Patient is 18-75 years old at the time of signing the informed consent form.
2. ECOG performance status 0-1.
3. Pathological confirmed or MRI/ enhanced CT confirmed pelvic recurrence.
4. No distant metastasis lesions outside the pelvic.
5. No prior radiotherapy within 6 months.
6. Participants with pelvic recurrence who have not previously been treated with first-line chemotherapy.
7. Life expectancy at least 24 weeks.
8. 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.
9. Non pregnancy or lactation.
10. Fully informed and willing to provide written informed consent for the trial.

Exclusion Criteria:

1. Neutrophil < 1.5×10^9/L, PLT < 75×10^9/L.
2. TBIL > 1.5 ULN.
3. AST or ALT > 2.5 ULN, or ALT and / or AST > 5 ULN in patients with liver metastasis.
4. Cr > 1.5 ULN.
5. Serious electrolyte abnormalities.
6. Active coronary artery disease, severe/unstable angina, or newly diagnosed angina or myocardial infarction within 12 months.
7. Arterial thrombosis or deep vein thrombosis within 6 months, such as cerebrovascular accidents (including transient ischemic attacks), pulmonary embolism, deep vein thrombosis.
8. Congestive cardiac failure ≥ NYHA grade 2.
9. Human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS), untreated active hepatitis (hepatitis B defined as HBV-DNA ≥ 500 IU/ml; hepatitis C defined as HCV-RNA higher than lower limit of detection) or hepatitis B and hepatitis C virus co-infection.
10. Active inflammatory bowel disease or other colorectal diseases that lead to chronic diarrhea.
11. Suspected autoimmune disease.
12. Interstitial lung disease, non-infectious pneumonia or uncontrollable systemic diseases (such as diabetes, hypertension, pulmonary fibrosis and acute pneumonia).
13. Suspected allergic to any drugs used in the trial.
14. History of any immune checkpoint inhibitor therapy.
15. Clinically detectable second primary malignancy, or history of other malignancies within 5 years.
16. 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.
17. 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.
18. Serious mental abnormalities.