Left Ventricular Motion Integration in Computed Tomography Based on 3D Echocardiography for the MATRIX-VT Study

Stereotactic arrhythmia radioablation (STAR) therapy is a novel treatment for ventricular tachycardia that delivers a high radiation dose to a target volume in the myocardium. Recent publications have recommended the use of cardiorespiratory motion management strategies to prevent damage to nearby critical structures in addition to the commonly applied 5 mm margin of delivery uncertainty in radiation planning. Motion capture in 3D cardiac ultrasound (US) could be utilized for passive and active motion management due to its capability of capturing cardiac motion in 3D with a sufficient frame rate, and due to its advantages like small hardware components as well as real time capability. The transfer of patient-specific cardiorespiratory motion trajectories from US to computed tomography (CT) coordinates for the purpose of radiation plan adaptation presents a novel use-case that necessitates the combination of multiple image processing methods. In this work, we present a framework for motion capture in US developed for the evaluation of a clinical study. 3D/3D registrations of Cartesian and anatomic representations based on a spherical harmonics shape model are evaluated utilizing a human phantom dataset as well as seven patient datasets. Overall numeric results indicate accuracies of less than 5 mm error, and the use of the anatomic shape modelling increases tracking precision. Integration of patient-specific trajectories of the target or critical structures in CT could already be used for passive motion management in STAR therapy. The implemented framework has the potential to increase precision and safety of the therapy and to be further developed into an active motion management system in the future.