Repositioning accuracy of cerebral fractionated stereotactic radiotherapy using CT scanning

Purpose: To evaluate the accuracy of patient repositioning in fractionated cerebral stereotactic radiotherapy using a Brain Lab stereotactic cranial mask in conjunction with standard dental fixation. Patients and methods: Fifty planning and checking CT scans were performed in 25 patients. The check CT scan was performed before or after one of the three sessions of treatment. Co registration to the planning CT scan was used to assess alignment of the iso centre to the reference markers. The relative position of the P.T.V. with regard to iso centre allowed us to determine its total displacement (3-dimensional vector). Results: Mean iso centre translations (± S.D.) taking into account direction were -0.01 ± 0.7, -0.2 ± 1.3 and 0.07 ± 0.5 mm in medio-lateral, cranio caudal and anteroposterior directions respectively. Mean rotations (±S.D.) were -0.02 ± 0.6, -0.08 ± 0.3 and -0.1 ± 0.3 degree in medio-lateral, cranio caudal and anteroposterior axes respectively. Mean overall P.T.V. displacement was 1.8 ± 1.5 mm. P.T.V. displacement was smaller than 2 and 3 mm in 19/25 and 23/25 patients respectively. Conclusion: The accuracy of patient positioning using a stereotactic cranial mask system is similar to those reported in the literature and shows a satisfactory reproducibility with a standard dental fixation. (authors)