Accuracy in target localization in stereotactic radiosurgery.

The accuracy in target localization of CT, MRI, and digital angiography and the isocentric deviation of linear accelerator were investigated for stereotactic radiosurgery. Twenty-five slice images using CT and MRI were obtained out of geometrical phantom which was designed to produce exact 3-dimensional coordinates of several points within a 0.1 mm error range. These diagnostic images were transferred to a 3-D treatment planning system through ethernet. Measured 3-D coordinates of these images from the planning system were compared to known values by geometrical phantom. Anterior-posterior and lateral films were taken by digital angiography for measurement of spatial accuracy. The accuracy of gantry isocenter aligned by laser localizer was also measured. Lead ball was located at the isocenter of linear accelerator and x-ray films were taken by 4-MV photon beam with gantry angles of 0, 90, 180 and 270 degrees, Overall procedure from CT scanning to treatment was carried out using the geometrical phantom. The target accuracy was verified by high energy x-ray portal film. The accuracy of diagnostic machines were within 2.1 mm except MR-axial images. In case of linear accelerator, the deviation of isocenter was within 0.7 mm. Finally, the total isocentric deviation of overall procedure was 1.3 +/- 0.5 mm (using CT localization).