SBRT + PD-1 Antibody in Unresectable Locally Recurrent Rectal Cancer（SPARKLE）

This is a prospective study to delve into the therapeutic benefits of combining stereotactic body radiation therapy (SBRT) with PD-1 monoclonal antibody treatment for patients with unresectable locally recurrent rectal cancer (ULRRC). Our aim is to ascertain the safety of this approach and to offer robust, evidence-based medical guidance for the management of ULRRC using this innovative combination therapy. Researchers will combine SBRT with PD-1 for ULRRC to see if this treatment can provide a benefit of survival. Participants will: 1. Receive chemotherapy combined with PD-1 therapy for 1 cycle → SBRT treatment → Chemotherapy combined with PD-1 therapy for 3-6 cycles (assessment 6 weeks after SBRT treatment) → Surgery/Maintenance therapy. 2. Visit the clinic once every 3 months for checkups and tests