To Evaluate the Efficacy/Safety of Osimertinib Prior to CRT and Maintenance of it With Stage III, Unresectable NSCLC With EGFR Mutations

The study duration will be approximately 2 years for recruitment and 2 years of follow-up from the last patient's initiation into the study. The induction treatment with osimertinib will be up to 8 weeks, followed by 6 weeks of CRT treatment and osimertinib maintenance treatment until PD or death. The visit frequency will be every 2 weeks to 4 weeks during the induction treatment period, every 3 weeks during the CRT period (every 3 weeks for chemotherapy and daily visits for RT), and every 12 weeks during the osimertinib maintenance treatment period.