CAIX PET/ CT Guided Radiation Therapy in CcRCC.

This is a prospective, single-arm study in adults with recurrent or metastatic clear cell renal cell carcinoma (ccRCC). Participants will receive standard systemic therapy (targeted therapy plus anti-PD-1 immunotherapy) and undergo dual PET/CT imaging (FDG PET/CT and a CAIX-targeted PET/CT) to map disease sites. When feasible, PET/CT-visible lesions will be treated with image-guided stereotactic ablative radiotherapy (SABR). Patients will be followed to evaluate progression-free survival, local control of treated lesions, and treatment-related adverse events (planned enrollment: \~70).

Inclusion Criteria: Adults (≥18 years) Histologically confirmed clear cell renal cell carcinoma Recurrent or metastatic disease Planned or ongoing first-line systemic therapy (targeted therapy plus anti-PD-1 immunotherapy) Dual PET/CT imaging available (FDG PET/CT and CAIX-targeted PET/CT) and eligible for radiotherapy planning Multidisciplinary assessment confirms radiotherapy is feasible to treat ≥75% of detectable lesions Able to provide written informed consent Exclusion Criteria: Unable to receive stereotactic radiotherapy as planned Uncontrolled serious comorbidities or active infection Pregnant or breastfeeding Unable or unwilling to comply with study procedures and follow-up