A dose-limiting toxicity (DLT) is defined as an adverse event or abnormal laboratory value assessed as unrelated to disease, disease progression, inter-current illness/injury, or concomitant medications that occurs within the DLT observation period of \[177Lu\]Lu-NeoB. The National Cancer Institute Common Terminology Criteria for Adverse events (NCI CTCAE) version 5.0 will be used for all grading. In Group 1 (newly diagnosed GBM), the DLT observation period is defined as a total of 8 weeks (56 days) from the first administration of \[177Lu\]Lu-NeoB, to cover the entire duration of concomitant RT and TMZ combination with the first two administrations of \[177Lu\]Lu-NeoB. In Group 2 (recurrent GBM), the DLT observation period is 6 weeks (42 days) starting from the first administration of \[177Lu\]Lu-NeoB (at Week 1 Day 1) and accounting for assessment of the safety profile during 2 full cycles of \[177Lu\]Lu-NeoB.