Optimized Volumetric Modulated Arc Technique for Noninvasive Cardiac Ablation to Treat Ventricular Tachycardia

Abstract

Recent publications (Cuculich et al., NEJM-2017, Robinson et al., Circulation-2019) have shown promising outcomes of radioablation using a single-fraction SBRT to treat patients with refractory, life-threatening, VT. This prompted growing interest across the world to use SBRT to treat VT. The primary goal of this study is to explore an alternative VMAT planning technique to achieve greater Non-Target Heart-Tissue (NTHT) sparing while simultaneously allowing for breath hold (BH) treatments. 13 patients were selected who previously received a single fraction dose of 35 Gy to ITV and 25 Gy to PTV utilizing 3 non-coplanar VMAT arcs of 6 MV photon beams using HD-MLC on a radiosurgery-optimized linac. To further improve NTHT sparing we retrospectively re-planned each patient using 10 ipsi-lateral arcs with optimal gantry, couch and collimator angles. Two plans were generated using 6X FFF and 10X FFF beams with dynamic jaw-tracking. Gantry arc lengths were limited to 90° (< 15s/arc) for feasibility of a potential BH treatments. Couch angles were limited to ± 15° to avoid collisions. Plans were optimized to maximize the NTHT sparing while meeting the protocol constraints for the stomach, esophagus and colon (OAR). Plan quality metrics for both clinical and reoptimized plans are summarized in Table 1. Revised plans showed adequate target coverage (V95%Rx=>95%), better dose conformity and gradient, while meeting the dose constraints of the OARs. Excellent NTHT sparing is achieved by reducing the volumes of V20Gy by 43 cc and V5Gy by 250 cc. Average mean dose reduction of 2.5 (range: 0.6 – 6.0) Gy and 2.2 (0.7 – 5.7 Gy) was observed in 6X FFF and 10X FFF plans, respectively. Revised plans showed the possibility of treating each arc in a single BH. The standardized technique used in this study showed improved NTHT sparing and better dose conformity. This result may be important for the group of patients where cardiac toxicity may play a vital role in long-term survival. BH treatments may reduce the required PTV margins resulting in further NTHT sparing.Abstract 3778; Table 1Vol. (cc)Plan TypeTarget CoverageConformityMean D (Gy)%VRx%V95%RxConformity IndexGradient MeasureITV48.1 ± 29Clinical38.4 ± 1.197.6 ± 2.499.7 ± 0.66X FFF36.9 ± 0.494.2 ± 3.199.3 ± 0.810X FFF36.8 ± 0.890.5 ± 11.698.7 ± 2.0PTV138.9 ± 67.8Clinical33.6 ± 1.199.0 ± 0.899.7 ± 0.41.14 ± 0.122.01 ± 0.476X FFF32.3 ± 0.493.8 ± 2.596.8 ± 2.21.02 ± 0.041.76 ± 0.4710X FFF32.3 ± 0.494.2 ± 2.397.1 ± 1.81.03 ± 0.031.55 ± 0.26Non-Target Heart TissueMean D (Gy)%V25%V20%V15%V10%V5%V2Clinical6.2 ± 2.10.9 ± 0.84.9 ± 2.511.2 ± 5.421.4 ± 9.140.5 ± 13.966.7 ± 17.86X FFF3.7 ± 1.10.3 ± 0.31.9 ± 2.74.9 ± 1.610.1 ± 3.622.5 ± 8.945.9 ± 15.7Vol. spared (cc)9 ± 1143.± 3590 ± 76160 ± 113250 ± 146284 ± 20910X FFF4.0 ± 1.10.4 ± 0.32.2 ± 0.75.5 ± 1.711.4 ± 3.825.5 ± 9.649.6 ± 16.5Vol. spared (cc)8 ± 1039 ± 3381 ± 75142 ± 108208 ± 111233 ± 150 Open table in a new tab