This is a single-arm, multicenter, open-label, phase Ⅱ exploratory clinical study, which plans to enroll 74 treatment-naive patients with EGFR-sensitive mutations (exon 19 deletion, exon 21 L858R mutation) and symptomatic brain metastases from non-small cell lung cancer (NSCLC). The primary objective is to evaluate the intracranial progression-free survival (iPFS) of hippocampal-sparing whole-brain radiotherapy (PTV: 20Gy/10 fractions) combined with simultaneous integrated boost to brain metastases (PGTV: 40Gy/10 fractions) plus osimertinib (80mg orally once daily). The secondary objectives are to assess efficacy indicators including overall progression-free survival (PFS), intracranial/systemic objective response rate (ORR), as well as safety. The primary endpoint is iPFS, supplemented by secondary endpoints such as PFS, ORR, disease control rate (DCR), overall survival (OS), adverse events (AE) evaluated per NCI-CTCAE v5.0 criteria, and neurocognitive function scores (MMSE/HVLT-R). By optimizing the combined mode of radiotherapy and targeted therapy, this study aims to provide a safer and more effective treatment option for such patients, balancing tumor control and quality of life protection.