This prospective observational study aims to evaluate symptom burden and symptom clusters among lung cancer patients undergoing definitive concurrent chemoradiotherapy (CRT), based on electronic patient-reported outcomes (ePROs). Patients will complete the validated MDASI-LC and EQ-5D instruments weekly from baseline through the end of CRT and for 12 weeks post-treatment. The study will characterize the longitudinal trajectories of symptom severity and interference, identify distinct symptom clusters and their temporal patterns, and explore patient-level predictors of symptom burden. The findings may support the development of personalized symptom management strategies and improve quality of life during and after CRT.