Integration of electro-anatomical maps in the planning phase of stereotactic arrhythmia radioablation for refractory ventricular tachycardia

Abstract

Abstract Introduction Despite the efficacy of stereotactic arrhythmia radioablation (STAR) for the treatment of refractory ventricular tachycardia (VT), the planning phase to precisely delineate the arrhythmogenic substrate still suffers from limitations due to the incompatibility of data formats between 3D electro-anatomical mapping systems (EAM) and STAR planning software (CyberKnife). Purpose Within the STOPSTORM European consortium, we present a workflow to integrate all 3D EAM data (e.g. voltage, activation time, anatomical tags) into the STAR planning software using the open source software Slicer3D to improve targeting of the arrhythmogenic substrate. Method Two protocols were compared retrospectively. Protocol 1 (STAR gold-standard) comprised the manual contouring of the clinical target volume (CTV) on planning 4D-CAT SCAN drawn side-by-side using EAM (Carto3, Biosense Webster) screen-shots and diagnostic reports. Protocol 2 comprised semiautomatic segmentation of CTV on planning 4D-CAT SCAN using imported EAMs annotated with landmarks for VT target delimitation. The semiautomatic segmentation of CTVs included three steps: (1) semiautomatic segmentation of ventricular myocardium (VM), the blood-pool of the concerned ventricle and at least two additional cardiac cavities; (2) 3D alignment of EAM with the segmented cavities; and (3), 3D delineation of CTV identified as the transmural section of VM segment surrounding the EAM’s VT target delimited by the annotated landmarks. The volume overlap (Dice coefficient) and the absolute difference of the CTVs obtained with the two protocols were compared. Both measurements were expressed in percentage as follows: Dice coefficient 0% means no overlap and 100% complete overlap; absolute difference of volumes 0% means no difference and 100% means that one CTV was twice the size of the CTV generated by the other protocol. Results Both protocols were applied to four patients (65.5 ± 8.5 yo) with refractory VT successfully treated with STAR. Figure 1 shows an example (Patient 1) of the CTV contouring using the CARTO EAMs aligned with the CT images in Slicer3D. Figure 2 illustrates significant mismatch between the segmented CTVs of the two protocols. The median volume overlap of the CTVs was 44%, while the median volume absolute difference was 35%. Table 1 reports detailed results. Conclusion Our study reveals a high variability of CTV delineation for STAR using two different protocols. The intraprocedural assignment of anatomical landmarks for VT target delimitation on EAM appears promising to improve CTV delineation. Further research is needed to evaluate the correlation between STAR outcome and CTV delineation accuracy.