Additional Study Information: The purpose of the study is to evaluate the safety of Lutathera alone in patients with recurrent glioblastoma and the combination of Lutathera with radiotherapy with temozolomide (TMZ) in patients with newly diagnosed glioblastoma (GB) and to establish the appropriate dose of this combination. Lutathera is a radioligand therapy, which is a targeted treatment that selectively delivers radiation to the tumor, with limited damage to surrounding tissues. Lutathera uses a radioactive particle (lutetium-177) attached to a targeting compound that binds to a specific protein on the tumor cells (somatostatin receptor type 2). Once administered through infusion into the bloodstream and bound to the receptor, Lutathera goes inside the tumor cells, where the radioactive component damages them from within. Lutathera is already approved in Europe, North America and several other countries for the treatment of neuroendocrine tumors in adult patients (under the name Lutathera). It has been administered to more than 9,000 patients with neuroendocrine tumors. However, this is the first study where Lutathera will be administered in combination with radiotherapy with or without temozolomide in patients with newly diagnosed glioblastoma.