ESTRO 2023 - Abstract Book

S789

Monday 15 May 2023

ESTRO 2023

Purpose or Objective In patients with refractory ventricular tachycardia (VT), STereotactic Arrhythmia Radioablation (STAR) showed promising results for otherwise untreatable patients. The STOPSTORM.eu project coordinates European efforts to clinically validate STAR and to refine protocols and guidelines. The aim of this work is to present the current clinical STAR practise in Europe based on three examples as baseline for further optimization. Materials and Methods Target Volumes (TV) and Organs-at-Risk (OAR) were generated from previous consortium benchmarks and consensus definitions for three well-selected STAR cases. Planning Target Volumes (PTV) were generated based on three different compensation strategies for cardiac and respiratory motion and overlapped/close OARs like coronary arteries or stomach. The STOPSTORM.eu members were asked to generate single fraction treatment plans with 25 Gy dose prescription based on ICRU report 91 for each case based on their STAR clinical practise through multi-disciplinary discussion. Resulting dose distributions were analysed independently using a customized platform for multi-center treatment planning studies and possible dosimetric endpoints were discussed with participants in a workshop. Results Most of the submitted plans (75%) employed Intensity Modulated Arc Therapy (IMAT) with 6 MeV FFF beams (73% of the IMAT plans) among other commonly used techniques for stereotactic radiotherapy. Presently, used guidelines for STAR treatment planning and OAR dose limits vary. As a major finding, 73% of the submitted plans showed close OAR sparing over achieving high PTV coverage (Figure 1) and the consortium agreed on a maximum dose to the stomach of 19 Gy, arguing that lower doses may also result in clinical efficiency. Cases 1 and 3 dose distributions (referenced as A. and C. in Figure 2) highlighted how OARs sparing also resulted in heavy PTV under dosing for some plans. Eventually, the participants decided not to underdose PTV to spare coronaries (avoiding hotspots on the overlap) if side effects are manageable.

Figure 1: DVH (Dose-Volume Histogram) distributions for all participants for relevant structures in the three benchmark cases. Different delivery techniques, planning strategies, prescription methods and followed guidelines explain the differences in PTV coverage and OAR sparing. The red line indicates the mean DVH and the shadowed line shows the range of the plots among the centres.