Stereotactic Radiotherapy Ablation and Atrial Fibrillation: Technical Issues and Clinical Expectations Derived From a Systematic Review

Abstract

AimThe purpose of this study is to collect available evidence on the feasibility and efficacy of stereotactic arrhythmia radio ablation (STAR), including both photon radiotherapy (XRT) and particle beam therapy (PBT), in the treatment of atrial fibrillation (AF), and to provide cardiologists and radiation oncologists with a practical overview on this topic.MethodsThree hundred and thirty-five articles were identified up to November 2021 according to preferred reporting items for systematic reviews and meta-analyses criteria; preclinical and clinical studies were included without data restrictions or language limitations. Selected works were analyzed for comparing target selection, treatment plan details, and the accelerator employed, addressing workup modalities, acute and long-term side-effects, and efficacy, defined either by the presence of scar or by the absence of AF recurrence.ResultsTwenty-one works published between 2010 and 2021 were included. Seventeen studies concerned XRT, three PBT, and one involved both. Nine studies (1 in silico and 8 in vivo; doses ranging from 15 to 40 Gy) comprised a total of 59 animals, 12 (8 in silico, 4 in vivo; doses ranging from 16 to 50 Gy) focused on humans, with 9 patients undergoing STAR: average follow-up duration was 5 and 6 months, respectively. Data analysis supported efficacy of the treatment in the preclinical setting, whereas in the context of clinical studies the main favorable finding consisted in the detection of electrical scar in 4/4 patients undergoing specific evaluation; the minimum dose for efficacy was 25 Gy in both humans and animals. No acute complication was recorded; severe side-effects related to the long-term were observed only for very high STAR doses in 2 animals. Significant variability was evidenced among studies in the definition of target volume and doses, and in the management of respiratory and cardiac target motion.ConclusionSTAR is an innovative non-invasive procedure already applied for experimental treatment of ventricular arrhythmias. Particular attention must be paid to safety, rather than efficacy of STAR, given the benign nature of AF. Uncertainties persist, mainly regarding the definition of the treatment plan and the role of the target motion. In this setting, more information about the toxicity profile of this new approach is compulsory before applying STAR to AF in clinical practice.

Non-Oncological Radiotherapy: A Review of Modern Approaches

“…The main favorable finding consisted in the detection of electrical scar in 4/4 patients undergoing specific evaluation, whereas the minimum dose for efficacy was 25 Gy. No acute complications were observed below this dose and a great heterogeneity was observed among the included studies [ 22 ].…”

Phase II Trial of LINAC-Based STereotactic Arrhythmia Radioablation (STAR) for Paroxysmal Atrial Fibrillation in Elderly: Planning and Dosimetric Point of View

“…Since there are no other analyses in the literature about the use of LINAC for AF-STAR, we could only compare these results with a few published cases performed with a different technology (Cyberknife) [18,19]. As previously reported, the target definition was not the same.…”

“…In the Cyberknife cases, the PVs and the left atrial posterior wall were irradiated. The mainstay AF ablation approach is PVs isolation, while appropriate/effective ablation targets, including the atrial wall, remain poorly defined [1,18,19]. Thus, in the present trial, the target was defined as the area around the PVs, defined by radiation oncology and cardiology (Figures 1 and 2).…”

Precision requirements in stereotactic arrhythmia radioablation for ventricular tachycardia

“…Treatment precision requirements and the need for more complex active motion management are thought to be higher in STAR treatments for atrial fibrillation (AF) than VT, likely contributing to the relatively lower clinical uptake and success of STAR for AF [42,43]. Reasons for this include the combination of target motion complexity, target motion magnitude and target proximity to critical structures [43], as well as differing antiarrhythmic radiobiology mechanisms and requirements, and the favourable life expectancy and health of the AF patient cohort [42]. The risk-benefit profile for treating benign AF with STAR therefore leans towards ensuring safety, particularly considering current knowledge gaps regarding treatment toxicities.…”