A Single Institution's Experience with Cardiac Radioablation Utilizing the 17-Segment Model for Target Localization

Abstract

<h3>Purpose/Objective(s)</h3> Ventricular arrhythmias (VT and Vfib) account for most sudden cardiac deaths, killing 300,000 per year in the US. Cardiac radioablation (CRA) utilizes SBRT to ablate foci that cannot be otherwise managed with anti-arrhythmics (AAs) or catheter ablation. For radiation oncologists, successfully implementing CRA is difficult as there is little formal training in ventricular anatomy. Herein we report our institution's experience treating 11 patients with refractory VT utilizing the American Heart Association (AHA) 17-segment model of left ventricular anatomy. <h3>Materials/Methods</h3> Patients were considered for treatment with CRA if they had refractory VT despite AAs and either 1) had undergone unsuccessful catheter ablation(s), or 2) were unable to tolerate catheter ablation for medical/technical reasons. All CRA cases were planned by a multidisciplinary team (MDT) including electrophysiologists (EPs), radiation oncologists, and radiation physicists. The targets were determined by EP based on available diagnostic testing and their locations were defined as including part/all of several segments in the AHA 17-Segment model (patient 7′s target included the right ventricular outflow track, see table). Axial images from 4D CT simulation were reoriented to the cardiac-specific coordinate system employed in AHA 17-segment model, utilizing our published protocol. Targets were delineated by the MDT with appropriate expansions to account for respiratory motion and uncertainty. CRA was delivered with 25 Gy in a single fraction. Follow up included H&P and interrogation of patients' Automatic Implantable Cardioverter Defibrillators (AICDs), which provided data on instances of anti-tachycardia pacing (ATPs), shock therapy and total burden. To assess treatment efficacy, AICD interventions/month were compared prior to and after CRA using the Wilcoxon matched pairs sign rank test. <h3>Results</h3> Between 1/2020 and 12/2021, 11 patients underwent CRA at our institution, 9 of whom had at least 2 months of follow up before and after treatment as recorded by their AICD (median follow up 12 months and 12 months, respectively). Four patients also underwent cardiac sympathetic denervation prior to CRA. Prior to CRA, median ATP/month, shocks/month, total burden/month were 1.15, 0.56, and 2.31, which significantly decreased to 0.11, 0.00, and 0.11 after CRA (p < 0.05, p < 0.01, p < 0.05, respectively). Except one, all patients had a decrease in ATP and total burden. All 9 patients experienced a decrease in shock burden, and 6 remain shock-free since CRA. In the 11 patients treated, there were no CTCAE grade >1 toxicities that were attributable to CRA. <h3>Conclusion</h3> In our relatively large singe-institution CRA experience, the AHA 17-segment model has proven to be an effective means of communicating target location, facilitating excellent clinical outcomes with most patients remaining shock-free after treatment.