Rotational and translational reproducibility of newly developed Leksell frame-based relocatable fixation system

Purpose. The aim of this study was to evaluate three-dimensional movement of the cranium in a relocatable frame using positions of anatomical landmarks obtained from repeated quality-assurance (QA) computed tomography (CT) studies. Materials and methods. We analyzed 17 series of QA-CT data representing five patients who underwent stereotactic radiotherapy for treatment of acoustic neurinoma. Helical-CT scans with 1-mm collimation were obtained at the time of treatment planning and during the course of treatment. The right and left short processes of the incus and the top of the crista galli were used as the three anatomical reference points. Results. Fluctuations in distance among the reference points were all <1 mm. The translational displacements for these points were <2 mm, with standard deviations (SD) of <2 mm. A plane that included all three reference points was defined as the reference plane. To investigate the direction of cranial rotation for each QA-CT scan, unit normal vectors of the reference plane were obtained. Three-dimensional analyses indicated that cranial rotation was greatest along the X-axis, followed by the Y-axis, with the least rotation along the Z-axis. Conclusion. The result suggested that movement of the craniocaudal axis in the sagittal plane was a major factor behind displacement of the cranium.