Cardiac radioablation

Ventricular tachycardia (VT) is one of the main contributing factors to sudden cardiac death (SCD). VT describes a sudden acceleration in the heart rhythm up to a level where the normal blood pumping function of the ventricles cannot be maintained. It is indicative of a disruption or disturbance of the normal cardio-electrical circuit induced by myocardial scar tissue. In Europe, the annual incidence of SCD is approximately 50-100 per 100,000 inhabitants [Fishman 2010]. This corresponds to approximately 500,000 cases of SCD per year. The current standard-of-care is to use cardioprotective and anti-arrhythmic drugs, antitachycardia pacing and/or shocks delivered by an implantable cardioverter-defibrillator (ICD), and invasive catheter ablation for drug-refractory VT. Unfortunately, VT recurs in 30-50% of all patients within one year of catheter ablation. Very recently, advances in both cardiology and radiotherapy have given rise to a new non-invasive salvage treatment for VT: STereotactic Arrhythmia Radioablation (STAR). STAR has been named in analogy to Stereotactic Ablative Body Radiotherapy (SABR). Typically, a single fraction dose of 25 Gy is applied to ablate the ventricular target [Cuculich 2017]. It is estimated that <200 patients have been treated so far worldwide, mostly under compassionate care protocols, or limited phase I/II trials. Remarkably, despite the ad-hoc nature of cardiac radioablation, STAR has reportedly reduced the VT burden by >90% with a favourable toxicity profile [Robinson 2019]. Within Europe, we have initiated the H2020-funded STOPSTORM consortium (#945119), in an effort to consolidate all European cardiac radioablation initiatives. By pooling data from more than 30 participating centres, we hope to comprehensively demonstrate the safety and efficacy of STAR. Cleary, the effectiveness of STAR hinges on the accuracy of targeting, and the precision of the irradiation. Ideally, treatment would eradicate the arrhythmia focus while also avoiding radiation-induced toxicities in healthy tissue. This is especially difficult in the heart, which is subject to complex cardiorespiratory motion, while itself being considered a very important organ-at-risk. In this presentation, I will address the three key factors (3Ts) that could impede the widespread adoption of STAR. Targeting: Identifying the relevant electrophysiological (EP) substrate for STAR is the first key challenge. Treatment: Ablating the EP target, subject to complexcardiorespiratory motion, while minimizing radiation-induced toxicities is the second key challenge. Toxicity: Keeping track of acute and longer-term radiation-induced side effects of STAR is the third key challenge. A special focus of this presentation will be on STAR using hybrid MRI/radiotherapy (MR-linac) devices to maximize treatment precision by tracking patients’ every heartbeat and breath during irradiation.