125I Seed Implantation Plus Systemic Therapy for Oligoprogressive NSCLC or Colorectal Cancer

This is a prospective, open-label, randomized phase 2 controlled trial enrolling adults with histologically confirmed metastatic NSCLC or colorectal cancer who developed extracranial oligoprogression (≤5 progressive lesions) on PET/CT or CT while receiving at least first-line systemic therapy (including maintenance). Eligible patients will be randomized 1:1 to (1) standard-of-care systemic therapy per treating physician discretion, or (2) image-guided 125I seed implantation to all oligoprogressive lesions plus standard-of-care systemic therapy. Oligoprogression will be determined by predefined imaging response criteria (RECIST and/or PERCIST, depending on baseline imaging modality), with confirmation by designated study radiologists. Follow-up imaging will be performed at 8 weeks (±2 weeks) after randomization and every 12 weeks (±2 weeks) thereafter to assess disease status. The primary endpoint is progression-free survival measured up to 12 months. Secondary endpoints include overall survival, time to initiation of a new systemic therapy, local control of implanted lesions, safety, and quality of life. Optional exploratory objectives may include circulating tumor DNA dynamics and metabolic PET parameters.