Comparing 68Ga-FAPI PET-Guided Abdominal Radiotherapy Combined With Second-Line Standard Therapy and Cadonilimab Versus Second-Line Standard Therapy in Colorectal Cancer With Peritoneal Metastasis

This study is testing a combination approach for colorectal cancer that has spread to the lining of the abdomen (called peritoneal metastasis). It compares standard second-line chemotherapy alone versus combining it with targeted radiation therapy guided by a special type of imaging scan (68Ga-FAPI PET) and an immunotherapy drug called cadonilimab. **You may be eligible if...** - You are 18 or older and have colorectal cancer confirmed to have spread to the abdominal lining - Your cancer progressed after first-line treatment (but you have NOT received immunotherapy) - You are in good enough health to tolerate treatment (ECOG 0–1) and expected to live at least 6 months - Your blood counts, liver, kidney, and clotting function are within acceptable levels **You may NOT be eligible if...** - You have very low blood counts, uncontrolled high blood pressure, or active bleeding or ulcers - You have significant heart disease, a recent stroke, or blood clots within the past 6 months - You have previously received immunotherapy (anti-PD-1/PD-L1 drugs) - You have active hepatitis B or C - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.