Key Inclusion Criteria:  Common Criteria:  Participant is >= 18 years on the day of signing informed consent form Histologically confirmed glioblastoma Adequate bone marrow, organ function and electrolyte values  Newly Diagnosed Glioblastoma:  Presence of Gadolinium enhancing tumor in pre-surgery magnetic resonance imaging (MRI) Karnofsky Performance Score (KPS) >= 70 %  Recurrent Glioblastoma:  Participant has experienced first or second recurrence of their glioblastoma, after standard or experimental therapy that includes prior radiation therapy Evidence of recurrent disease demonstrated by disease progression using modified Response Assessment in Neuro-Oncology (mRANO) criteria KPS >= 60 % [68Ga]Ga-DOTA-TATE uptake by positron emission tomography/computed tomography (PET/CT) or PET/MRI scan at the tumor region Presence of Gadolinium enhancement in the tumor region in MRI at the time of diagnosis of tumor recurrence  Key Exclusion Criteria:  Common Criteria:  Participant is receiving additional, concurrent, active therapy for glioblastoma outside of the trial Extensive leptomeningeal disease History of another active malignancy in the previous 3 years prior to study entry  Newly Diagnosed Glioblastoma:  • Any prior treatment for glioma of any grade  Recurrent Glioblastoma:  Early disease progression prior to 3 months from the completion of radiotherapy More than 2 prior lines for systemic therapy Previous treatment with bevacizumab