In patients with glioma, the tumor, radiotherapy as well as chemotherapy can disrupt cognitive function. Cognitive functioning can be evaluated by a cognitive screening instrument and/or comprehensive neuropsychological test batteries. The most well-known and convenient screening instrument is the Mini Mental-State Examination (MMSE). However, the MMSE is developed to assess dementia and does not include items related to executive function. As such, the MMSE is insufficient to assess frontal-subcortical network dysfunction associated with cognitive damage after irradiation. More sensitive cognitive tests should be administered to determine the effects of re-irradiation on cognition. There is however still little consensus on which test should be used. Although comprehensive neuropsychological test batteries are most sensitive, a brief cognitive screening is preferable in the present setting. For this trial, the investigators intend to use a number of relevant standard tests including the Hopkins Verbal Learning Test-Revised (HVLT-R, the Trail Making Test and Controlled Oral Word Association (COWA) as suggested by the Radiation Therapy Oncology Group (RTOG). The Stroop colour-word test (Stroop) is added to the battery in order to assess visual attention.