Implementing a Highly Non-Coplanar Arc Geometry for Radioablation of Refractory Ventricular Tachycardia: Presenting End-to-End Testing, Validation and Efficient Clinic Workflow
Abstract
Purpose
Noninvasive stereotactic radioablation for refractory ventricular tachycardia (rVT) using a single 25 Gy fraction is an emerging treatment option for patients with advanced heart failure. This complex procedure requires highly non-coplanar beam geometry, stringent dose constraints, and a well-defined clinical workflow. This study establishes institutional physics guidelines and workflow for cardiac rVT radioablation, with emphasis on treatment planning, image guidance, and quality assurance (QA).
Methods
Two radioablation plans (6MV-FFF, 10MV-FFF) were developed for in-house validation and end-to-end testing using a micro-MLC EDGE linac. Highly non-coplanar VMAT plans employed left-sided partial arcs with optimized collimator and couch angles. For a 48.4 cc rVT target, Acuros-based inverse planning was used to achieve conformal target coverage, steep dose gradients, and minimal dose to organ-at-risk (OAR), including heart-minu- PTV. Target coverage, conformity index (CI), gradient index (GI), and maximum doses to OARs were evaluated. Daily Winston–Lutz (WL) and patient-specific QA results were recorded.
Results
Both plans achieved excellent conformity (CI = 0.96) with steep dose gradients (GI = 2.52 for 6MV-FFF and 2.69 for 10MV-FFF). All OAR constraints were met, with maximum doses <4 Gy to spinal cord, <1.4 Gy to bronchus and stomach, and <5.7 Gy to esophagus. Mean dose to heart-minus-PTV was 3.5 Gy (6MV-FFF) and 3.7 Gy (10MV-FFF). The 10MV-FFF plan reduced beam-on time by 2.5 minutes due to lower modulation (MU: 9,282 vs 10,318). Daily WL results were <1 mm, and patient-specific QA pass rates exceeded 95% using 2%/2 mm criteria.
Conclusion
Highly non-coplanar VMAT radioablation for cardiac rVT achieved exceptional target conformality and reduced mean healthy heart dose (<3.7 Gy), substantially lower than reported values. The 10MV-FFF beam provided equivalent plan quality with shorter treatment time, potentially reducing intrafraction motion. Comprehensive end-to-end testing confirmed robust clinical deliverability. Independent dose verification using the IROC SBRT motion phantom is ongoing.