Frame stability and anatomical QA in radiosurgery

The aim of the study was to analyze whether the fixation of the stereotactic frame is stable and whether the location of the treated target coincides with its anatomical location during Gamma Knife® surgery (GKS). Stereotactic MR examinations using the same high-resolution MRI protocol were performed before and after GKS in 18 consecutive patients. The stereotactic (x,y,z) coordinates for three different anatomical landmarks were independently defined three times in each study for each landmark of the images taken before and after GKS by two of the authors, resulting in a total of 648 coordinate definitions. The uncertainty in the readings of the coordinates for the anatomical landmarks was of the same magnitude as the difference in the coordinates before and after GKS in all but one patient. The differences in this one case were due to MR distortion and not to repositioning of the frame. The difference in the coordinates before and after treatment was not affected by the removal of one of the frontal fixation screws in one of the patients. The stereotactic frame position is stable and does not move.