Phase II Elderly/Frail Pts With Newly Diagnosed or Recurrent Malignant Glioma Tx Treated With Cesium-131 GammaTile®

Inclusion Criteria: * Supratentorial * A bi-dimensionally measurable lesion of at least 10 mm, visible on two or more axial slices 5 mm apart. * The pre-operative tumor planned for resection is ≤ 7 cm in maximal dimension. * Tumor, which in the opinion of the enrolling neurosurgeon, is amenable to attempted gross total resection (GTR) or near total resection (NTR). * Anticipated GT placement (i.e., closest aspect of post resection tumor bed anticipated to receive GT placement) that is \> 15mm from the optic chiasm or brainstem. * If multifocal, must be fully resectable in one operative bed. Surgical protocol will follow current institutional standards. * Able to receive 5-aminolevulinic acid (5-ALA, Gleolan) or other institutionally standard immunofluorescent-guidance such as fluorescein, prior to surgery to optimize GTR or NTR of enhancing tumor. * Karnofsky Performance Scale (KPS) 1. Elderly GBM: baseline KPS score of ≥ 60. 2. Frail GBM: baseline (pre-GBM diagnosis) is \<70 and surgical management is expected to improve KPS to ≥ 60. Exclusion Criteria: * Staged surgery planned (prior biopsy allowed). * Bilateral tumors, or multi-focal tumors that cannot be encompassed in one operative field. * Spinal tumors are excluded. * Enhancing extension into brainstem or thalamus, or significant invasion into the corpus callosum that would preclude a high likelihood of GTR or NTR. * Leptomeningeal disease not expected to be encompassed by the surgical resection. * Evidence of diffuse leptomeningeal disease that requires whole brain irradiation are excluded from this trial.