Nuklearmedizin und Strahlentherapie

Six Degree-of-Freedom Image Guidance for Frameless Intracranial Stereotactic RadioSurgery with kilo-voltage Cone- Beam CT

Abstract

Zheng Chang, Zhiheng Wang, Jinli Ma, Q. Jackie Wu, Scott Senick, Ryan McMahon, John P. Kirkpatrick and Fang-Fang Yin

Abstract Purpose: To investigate localization accuracy for frameless intracranial stereotactic-radiosurgery using 2D orthogonal planar imaging and 3D cone-beam CT (CBCT) in 6-degree-of-freedom (6-DOF).

Methods and Materials: In a phantom study, a target ball phantom was used to perform a Winston-Lutz test and to verify coincidence of imaging isocenter and radiation isocenter. A head phantom was placed with pre-defined positions and imaged with CBCT to test imaging accuracy. In a patient study, one hundred patients were included. Patients were initially positioned with a thermoplastic frameless mask system and then aligned with orthogonal planar imaging and CBCT. The setup discrepancies were quantitatively analyzed.

Results: Phantom experiments showed discrepancies in root-mean-square were 1.6mm translationally and 0.5° rotationally between CBCT 6-DOF image guidance and the known displacements after deviations from the radiation isocenter are considered. In the patient study, setup displacements between orthogonal planar imaging and CBCT 6-DOF image guidance were 3.2mm translationally and 0.9° rotationally. The positioning of twelve patients was corrected in 6-DOF using CBCT and a robotic couch to reduce translational and rotational discrepancies of 1.4mm and 1.3°, as compared with standard CBCT translational correction. Conclusion: CBCT 6-DOF image guidance offers an explicit view to verify patient positioning in translations and rotations.