• Written informed consent, voluntarily signed and dated by the subject, must be obtained in accordance with regulatory and institutional guidelines before any procedures related to the study protocol that are not part of routine care are performed.

• Patients with pMMR/MSS colorectal adenocarcinoma;

• Age 18-75 years;

• Patients with histologically or cytologically confirmed colorectal cancer liver metastasis, with or without extrahepatic oligometastatic lesions, who are deemed by the hepatobiliary surgeon within the multidisciplinary team (MDT) to be ineligible for upfront R0 resection of liver metastases (unresectability is defined as one or more of the following conditions: ① Involvement of both left and right branches of the portal vein at the first hepatic hilum; ② Involvement of ≥2 hepatic veins at the second hepatic hilum; ③ No indication for upfront R0 resection/ablation after MDT discussion);

• Liver metastases are measurable by imaging (based on RECIST 1.1 criteria), with a maximum diameter of ≤6 cm;

• Patients who have not previously received radiotherapy for liver metastases, or whose liver tissue near the planned irradiation site has not been previously irradiated, and who have at least 700 cc of liver volume outside the treatment area;

• Previous hepatectomy, systemic chemotherapy, or local ablation therapy, or hepatic arterial infusion pump chemotherapy is allowed, with a washout period of 2 weeks;

• Child-Pugh score Class A ;

• ECOG performance status 0-1;

⁃ Peripheral blood counts and liver and renal function within allowable ranges (tested within 15 days before the start of treatment);

⁃ No history of other malignancies, not pregnant or breastfeeding, and effective contraception should be used during the study period and for 6 months after the last dose;

⁃ Life expectancy of ≥6 months.