SU‐EE‐A3‐02: Imaging Guided Frameless Stereotactic RadioSurgery Using CBCT 6D Image Registration and 6D Couch On Novalis Tx™ System

Abstract

Purpose: To investigate localization accuracy for image‐guided frameless stereotactic‐radiosurgery (IG‐SRS) using CBCT 6D image registration and 6D‐couch on Novalis Tx system. Method and Materials: Novalis Tx system is a powerful radiosurgery system featuring BrainLAB 6D‐couch and Varian CBCT. In this work, we performed phantom and patient studies to investigate IG‐SRS with CBCT 6D guidance. In phantom studies, a head phantom was positioned on couch, scanned with CBCT, and matched with planning CT using 6D image registration. Matching results were used to test accuracy of CBCT 6D/6D match for correcting translational and rotational setup errors. In patient studies, 10 intracranial SRS cases were randomly selected. Patients were initially positioned with BrainLAB mask system with target‐positioning‐overlays (TAPO). Patients were then scanned with CBCT, and positions were adjusted based on CBCT. Discrepancies between CBCT 3D/3D match and 6D/6D match were quantitatively analyzed. Results: Phantom experiments showed that translational discrepancies in root‐mean‐square (RMS) were 0.39, 0.23, and 0.36mm along lateral, longitudinal, and vertical directions. Rotational discrepancies in RMS were 0.38°, 0.19°, and 0.22° in pitch, roll, yaw, respectively. In retrospective patient studies, setup displacements measured in RMS between BrainLAB TAPO and CBCT 6D/6D match were upto 2.5mm translationally and 1.0° rotationally. If positioning was corrected using CBCT 3D/3D match, translational discrepancies in RMS were <0.5mm except 0.71mm in vertical, and rotational displacements in RMS were 0.67°, 0.88° and 0.22° in pitch, roll, yaw, as compared with CBCT 6D/6D match. CBCT guided 6D correction was performed in two cases to achieve necessary positioning accuracy. After 6D adjustments, translational and rotational displacements of upto 4mm and 0.9° were measured in CBCT 6D/6D match were fully corrected using 6D‐couch. Conclusion: CBCT 6D/6D match offers unprecedented view to verify patient positioning in both translations and rotations. Combined with 6D‐couch, translational and rotational setup errors can be effectively minimized.