This study evaluates hypofractionated radiotherapy combined with PD-1 inhibitor-based systemic therapy in patients with metastatic solid tumors. Eligible patients will be enrolled into three cohorts according to tumor type: metastatic hepatocellular carcinoma, metastatic renal cell carcinoma, and metastatic urothelial carcinoma. The study aims to assess the safety and therapeutic efficacy of combining localized radiotherapy with immunotherapy, with or without cohort-specific systemic agents.