A Target Definition based on Electroanatomic Maps for Stereotactic Arrhythmia Radioablation

•We propose Electroanatomic map based target localization for STAR.•EAM registration is sufficient to localize treatment region.•Five of 7 patients demonstrated a reduction in ventricular tachycardia events. Identifying the target region is critical for successfully treating ventricular tachycardia (VT) with single fraction stereotactic arrhythmia radioablation (STAR). We report the feasibility of target definition based on direct co-registration of electroanatomic maps (EAM) and radioablation planning images. The EAM consists of 3D cardiac anatomy representation with electrical activity at endocardium and is acquired by a cardiac electrophysiologist (CEP) during electrophysiology study. The CEP generates an EAM using a 3D cardiac mapping system anticipating radioablation planning. Our in-house software read these non-DICOM EAMs, registered them to a planning image set, and converted them to DICOM structure files. The EAM based target volume was finalized based on a consensus of CEPs, radiation oncologists and medical physicists, then expanded to ITV and PTV. The simulation, planning, and treatment is performed with a standard STAR technique: a single fraction of 25Gy using volumetric-modulated arc therapy or dynamic conformal arc therapy depending on the target shape. Seven patients with refractory VT were treated by defining the target based on registering EAMs on the planning images. Dice similarity indices between reference map and reference contours after registration were 0.809±0.059 and 0.575±0.199 for LV and LA/RV, respectively. The quality of the transferred EAMs on the MR/CT images was sufficient to localize the treatment region. Five of 7 patients demonstrated a dramatic reduction in VT events after 6 weeks. Longer follow-up is required to determine the true safety and efficacy of this therapy using EAM-based direct registration method.