A simple method for evaluating stereotactic accuracy of Magnetic Resonance Imaging and Computed Tomography Imaging in Frame Based Radiosurgery.

PURPOSE To design a simple and reproducible method with minimum uncertainty for evaluating the stereotactic accuracy of Computed Tomography imaging and Magnetic Reso-nance Imaging and to compare the results. METHODS 3D phantom has been designed with 1 mm diameter targets in eight sectors for stereotactic MR imaging and CT imaging. The phantom was connected to Leksell stereotactic frame and the images obtained are exported to treatment planning system. Leksell stereotactic coordinates (X, Y, Z) of the holes are determined in each slice and mean maximum errors were calculated along with 3D vector distances from center of stereotactic coordinate system (100,100,100) to five known Targets. The target volumes are calculated independently for each image data sets. RESULTS The mean of maximum absolute error estimated for MR images from the Siemens Magnetom vision MR unit were 0.46 mm (X-Axis), 1.66 mm (Y-Axis) and 2.11 mm (Z-Axis). Mean of absolute maximum error estimated using CT images from the Philips Brilliance 16 CT scanner were 0.29mm (X-axis), 0.51mm (Y-Axis) and 0.90mm (Z-Axis). 3D vector calculations were 0.38 mm for CT and 0.72 mm for MRI. No significant variation is noticed in volume calculations from both image data sets. CONCLUSION This study showed that accuracy and quality of stereotactic CT- imaging and MR-imaging are limited by localization devices and their designs in frame based Radiosurgery. This method is simple, direct and economical with good resolution and high reproducibility. KEYWORDS Stereotactic accuracy, Computed Tomography, Magnetic Resonance Imaging, frame based Radiosurgery.