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

Patients will begin SBRT treatment within 2 weeks after the first round of chemotherapy. Intensity-modulated radiation therapy (IMRT) technology will be used, with a target gross tumor volume (GTV) of 5-8Gy/5 sessions, a total dose of 25-40Gy equivalent to a biological effective dose (BED) of 37.5-72Gy, administered from Monday to Friday. For patients who have previously received pelvic radiotherapy, the re-irradiation dose will be 3-5Gy/5 sessions, a total dose of 15-25Gy equivalent to a BED of 19.5-37.5Gy, administered from Monday to Friday.

The PD-1 monoclonal antibody used is Sintilimab 200mg every 3 weeks

First-line chemotherapy regimen of rectal cancer, using a second-line regimen primarily based on fluorouracil, such as a tri-weekly CAPOX or a bi-weekly mFOLFOX6/FOLFIRI/FOLFOXIRI + targeted therapy