A 52-year-old man presents with a 3-month history of progressive headaches, morning vomiting, and recent-onset seizures. MRI brain shows a large intra-axial lesion in the left frontal lobe with heterogeneous enhancement, central necrosis, and significant peritumoral edema. Histopathology confirms WHO Grade IV glioblastoma multiforme with MGMT methylation status positive. What is the drug of choice for adjuvant chemotherapy following maximal safe surgical resection and concurrent chemoradiation?