The purpose of this clinical study should be that, in the context of planned resections of glial brain tumors, pieces of tissue (biopsies) are removed from the tumor at several specific locations before the actual tumor resection takes place. The aim of these biopsies in advance to the actual tumor resection will be to receive tumor tissue samples not altered in such a way that it is no longer adequate for further treatment. If not adequate, a so-called undergrading could occur, which means that the biological structure of the tumor is misjudged and further therapy does not achieve the desired effect in the patient. On the one hand, certain tumor regions can drift due to a brain shift which leads to inaccurate tissue removal, and on the other hand samples are not altered by pressure or bleeding. To carry out these biopsies, a robot positioning device (AutoGuide®) will be used that has already been approved and tested for this type of intervention. The use of the AutoGuide® is intended to ensure that the tumor sample is taken with the greatest possible precision.