3429 - Incorporating Electroanatomic Mapping Data into Radiation Treatment Planning for Stereotactic Cardiac Radioablation: A One-Year Follow-up

Purpose/Objective(s): Cardiac radioablation for ventricular tachycardia (VT) using stereotactic body radiation therapy (SBRT) in refractory patients or those unsuitable for conventional ablation is an evolving therapeutic paradigm with promising early results. However, accurately localizing the target area in the treatment planning system (TPS) remains a significant challenge, even with the use of the 17-segment cardiac contouring method; these uncertainties result in increased planning target volumes (PTVs) and increased toxicity. Electroanatomic mapping (EAM) data provides detailed and accurate information for localizing VT circuits, which electrophysiologists use for radiofrequency ablation procedures. Incorporating EAM data into the delineation of targets in the TPS could provide more accurate planning. We offer a step-by-step tutorial to facilitate offline fusion of standard Digital Imaging and Communications in Medicine (DICOM) CT simulation images with non-DICOM EAM maps in open-source 3D Slicer to bridge the interoperability divide between EAM and TPS software.

Materials/Methods: In two patients with refractory VT, we used EA Map Reader, an open-source 3D Slicer plugin, to import and read carefully annotated EAM data containing outlines of the ischemic scar, the ventricle, and any identifiable cardiac substructures into a DICOM format. Upon conversion, the software generates a closed surface representing the cardiac scar and substructures. The imported structure set is then fused with CT image slices and the mapped scar representing the arrhythmogenic endocardial/epicardial substrate is defined as our treatment target. Once fused, radiation treatment planning proceeds as standard practice and treatment is delivered as per standard of care.

Results: Both patients had previously undergone radiofrequency ablation yet remained refractory, as indicated by recurrent VT episodes observed via their Implantable Cardioverter Defibrillators (ICDs). Following SBRT, both patients responded quickly, as evidenced by a two-week follow-up that was earlier than the blank period reported in previous studies. One-year follow up with ICD integration and echocardiograms demonstrated complete resolution of VT without recurrence and an increase in ejection fraction with no treatment-related side effects observed.

Conclusion: Accurate incorporation of EAM maps into radiation TPSs facilitates utilization of EAM-defined cardiac substructures and targets as additional aids in defining target volumes for stereotactic cardiac radioablation. Our pipeline for EAM incorporation into the TPS serves as a critical bridge between functional information gathered by electrophysiologists and anatomic information used by radiation oncologists in delineating a treatment target with confidence, enhancing the effectiveness of SBRT and fostering closer collaboration between electrophysiology and radiation oncology, ultimately leading to more accurate and effective treatment outcomes.