Purpose: To report the feasibility of single fraction stereotactic arrhythmia radioablation (STAR) in patients with refractory ventricular tachycardia (VT) based on co-registration of electroanatomic (EA) map and planning images.
Methods: A cardiac electrophysiologist acquires EA maps using the Carto3® system (Biosense Webster, Irvine, CA, USA) and defines the target region during an electrophysiology study. The EA map consists of 3D cardiac anatomy and electrical activity at any given mapped point. The EA target map is registered to the planning CT by aligning the left-ventricle (LV), right-ventricle (RV), left-atrium (LA), and available reference structures with defined contours on the MR/CT image based on iterative closest point algorithm. In-house software was developed for converting the EA image format to DICOM and registering reference structures. The simulation, planning, and treatment is performed with a standard STAR technique: a single fraction of 25 Gy using volumetric-modulated arc therapy or dynamic conformal arc therapy depending on the target shape.
Results: Three patients with refractory VT were treated by defining the target based on registering EA maps and contours on MR/CT. Dice similarity indices between transferred reference map and contours are 0.83 ± 0.04 and 0.72 ± 0.04 for LV and LA/RV, respectively. The target area is confirmed based on the consensus of cardiac electrophysiologists and radiation oncologists and expanded to an internal target volume (ITV) and a planning target volume (PTV), which provides a 5-mm margin on the ITV.
Conclusion: The quality of the transferred map on the image was sufficient to localize the treatment region accurately although we continue to refine the transferred target map. Longer follow-up is required to determine the true safety and efficacy of this therapy.