objective: glioblastoma multiforme (gbm), one of the most common and aggressive malignant brain tumors, is highly resistant to radiotherapy. numerous approaches have been pursued to find new radiosensitizers. we used a picogreen and colonogenic assay to appraise the dna damage and cell death in a spheroid culture of gbm cells caused by iodine-131 (i-131) beta radiation in the presence of topote...