Personalized Ultrafractionated Stereotactic Adaptive Radiotherapy (PULSAR ) Combined With Anti-PD1，Chemotherapy and Target Therapy for Metastatic Colorectal Cancer

Radiation therapy will be delivered every 3 weeks on the PULSAR schedule to achieve optimal local control of metastatic cancer and augment the effects of sintilimab.

Sintilimab will be given at 200 mg q3w every 3 weeks and schedule to the next day of every pulses of radiation.

"First-line standard systemic therapies in cohort A include: FOLFOX/FOLIRI/XELOX+ bevacizumab, FOLFOX/FOLIRI/XELOX+cetuximab (KRAS/NRAS/BRAF WT and left-sided tumors only).~Second-line standard systemic therapies in cohort B include: FOLFOX/XELOX+ bevacizumab, FOLFOX/XELOX+cetuximab (KRAS/NRAS/BRAF WT), FOLFIRI/irinotecan+raltitrexed/irinotecan/+bevacizumab, FOLFIRI/irinotecan+raltitrexed/irinotecan/+cetuximab (KRAS/NRAS/BRAF WT), based on the previous first-line chemotherapy and adverse events."