Once intra-operative pathology was confirmed, one to two MDialysis 70 Microdialysis Brain Catheters (membrane length 10 mm; shaft length 60 mm; ref. no. P00049) were placed into contrast-enhancing and/or non-contrast peritumoral tissue (within 5 mm from the resection cavity). Post-operative non-contrast CT imaging confirmed catheter placement with identification of an enhancing gold tip. After transfer to the intensive critical care unit, the inlet tubing of the catheter was connected to a portable syringe pump (MDialysis 107 Microdialysis Pump, ref no. P000127), containing artificial CSF (Perfusion Fluid CNS, ref no. P000151) at a rate of 1 µl/min. A microvial was connected at the end of the outlet tubing to continuously collect dialysate samples. To account for the correction factor, fractional recovery of temozolomide by ICMD was calculated based on previous in vitro sampling using CMA 70 Microdialysis catheter . All microdialysis supplies were purchased from MDialysis, (Stockholm, Sweden).