ESTRO 2025 - Abstract Book

S3218

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

Purpose/Objective: Standard treatment for patients with recurrent ventricular tachycardia (VT) typically involves radiofrequency catheter ablation. In some cases however this treatment is infeasible or ineffective in reducing VT episodes. Recently, stereotactic arrhythmia radiotherapy (STAR) has shown promising results for these patients [1]. A key challenge with STAR is managing respiratory motion to accurately irradiate the VT substrate while minimizing radiation exposure to the surrounding organs at risk (OAR), e.g. the stomach. Previously we demonstrated that non invasive mechanical ventilation (NIMV) at 60 breaths per minute (brpm) with positive end-expiratory pressure (PEEP) reduced left diaphragm motion by 50%, stabilizing organ positions. We also observed an increase in lung volume, which appeared to favorably alter organ position for STAR in patients with an inferior wall target. This study aims to assess if NIMV at 60 brpm with PEEP increases the minimal heart-stomach distance sufficiently to reduce radiation exposure of the stomach during STAR. Material/Methods: Retrospective MRI data of 22 healthy volunteers trained for ventilation at 60 brpm with 15 cmH ₂ O PEEP was analyzed. Each volunteer had three 3D-MRI scans, obtained during NIMV, and in inhalation/exhalation breath-hold, which combined served as a surrogate for free breathing. Scans without a clear view of the heart and/or stomach were excluded. For each remaining scan, the heart and upper-stomach were delineated by the author, and optimized by a radiation-oncologist. For each 3D-MRI scan, the minimal heart-stomach distance was calculated. Differences between the respiratory strategies were assessed using the Wilcoxon signed-rank test (p<0.05). Results: After excluding scans without a clearly visible heart and/or stomach, 17 MRI sessions of N=17 [10M;7F] volunteers (median age, 54; range 19-67) remained for analyses. The minimal heart-stomach distance during 60 brpm with PEEP was significantly larger than those found on both the inhalation (median: 6.7 vs 3.3mm; p =0.04) and exhalation breath-hold (median: 6.7 vs 1.4mm; p <0.001).