Investigating multi-leaf collimator tracking in stereotactic arrhythmic radioablation (STAR) treatments for atrial fibrillation

Introduction: Stereotactic arrhythmia radioablation (STAR) is an emerging treatment option for atrial fibrillation (AF).However, it faces possibly the most challenging motion compensation scenario: both respiratory and cardiac motion.Multi-leaf collimator (MLC) tracking is clinically used for lung cancer treatments but its capabilities with intracardiac targets is unknown.We report the first experimental results of MLC tracking for intracardiac targets.Methods: Five AF STAR plans of varying complexity were created.All delivered 5×10 Gy to both pulmonary vein antra.Three healthy human target motion trajectories were acquired with ultrasound and programmed into a motion platform.Plans were delivered with a linac to a dosimeter placed on the motion platform.For each motion trace, each plan was delivered with no MLC tracking and with MLC tracking with and without motion prediction.Dosimetric accuracy was assessed with γ-tests and dose metrics.Results: MLC tracking improved the dosimetric accuracy in all measurements compared to nontracking experiments.The average 2%/2mm γ-failure rate was improved from 13.1% with no MLC tracking to 5.9% with MLC tracking (p<0.001) and 7.2% with MLC tracking and no motion prediction (p<0.001).MLC tracking significantly improved the consistency between planned and delivered target dose coverage.The 95% target coverage with the prescription dose (V100) was improved from 60% of deliveries with no MLC tracking to 80% of deliveries with MLC tracking (p=0.03). Conclusion:MLC tracking was successfully implemented for the first time for intracardiac motion compensation.MLC tracking provided significant dosimetric accuracy improvements in AF STAR experiments, even with challenging cardiac and respiratory-induced target motion and complex treatment plans.These results warrant further investigation and optimisation of MLC tracking for intracardiac target motion compensation.