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

This study is testing whether ultra-precise, adaptive radiation therapy (called PULSAR — Personalized Ultrafractionated Stereotactic Adaptive Radiotherapy) can help "wake up" the immune system to attack colorectal cancer that has spread. The idea is that high-dose, precisely targeted radiation may cause a systemic immune response. **You may be eligible if...** - You are between 18 and 75 years old - You have colon or rectal cancer that has spread (metastatic), with 10 or fewer metastatic sites, all safely treatable - Your cancer is confirmed as MSS/pMMR type (a specific genetic subtype) - Your general health (ECOG) is 0 or 1 **You may NOT be eligible if...** - You have MSI-H or dMMR cancer (a different genetic subtype) - You have had radiation therapy within the past 6 months - Your cancer has spread too widely to treat all sites - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.