Maximal diameter is defined as the largest one after measuring all the three axes (lateral, anteroposterior, and superoinferior). The volume can be defined by automatic segmentation using the Leksell GammaPlan planning software (Elekta Instruments AB, Stockholm, Sweden) on all MR data, including the preoperative images. The tumor size (maximal diameter) and volume can be measured on the serial MR imaging (MRI) 1).