ESTRO 2024 - Abstract Book

S4343

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

ESTRO 2024

Estimating delivered dose during stereotactic arrhythmia radioablation: a STOPSTORM consortium study

Pavel Dvorak 1 , Lukas Knybel 1 , Raoul R.F. Stevens 2 , Colien Hazelaar 2 , Luuk H.G. van der Pol 3 , Bartłomiej Tomasik 4 , Joanna Kamińska 4 , Oliver Blanck 5 , Wouter van Elmpt 2 , Martin F. Fast 3 , Jakub Cvek 1 1 University Hospital and Faculty of Medicine, Department of Oncology, Ostrava, Czech Republic. 2 GROW School for Oncology and Reproduction, Maastricht University Medical Center+, Department of Radiation Oncology (MAASTRO), Maastricht, Netherlands. 3 University Medical Center Utrecht, Department of Radiotherapy, Utrecht, Netherlands. 4 Faculty of Medicine, Medical University of Gdańsk, Department of Oncology and Radiotherapy, Gdańsk, Poland. 5 University Medical Center Schleswig-Holstein, Department of Radiation Oncology, Kiel, Germany

Purpose/Objective:

Stereotactic arrhythmia radioablation (STAR) has been suggested as a promising alternative in cases of failed catheter ablation for recurrent ventricular tachycardias in patients with structural heart disease. When delivering STAR, specific challenging conditions include extreme hypo-fractionation with typical single fraction prescription doses of 25 Gy and the target location in the left ventricle which makes it susceptible to cardiorespiratory intrafractional motion. The general objective of this work is to estimate the delivered dose based on data not explicitly considered and/or available for treatment planning. This includes situations where data was included only partially such as respiratory 4DCT or ECG-gated CT applied for target definition but not for dose calculation/optimization. In this initial study we analysed clinical available data of one STAR patient following a Cyberknife-specific workflow. In line with the general objective, the specific task was to provide a more accurate dose estimation by accounting for anatomical and dosimetric variations at complementary respiratory phases sampling free breathing during dose delivery. Prescribed dose was 20Gy for clinical reasons. The target comprised segments 4, 5, 6, 11, 12 and 16 of the AHA 17 segment heart model [e.g., 1]. Clinical STAR treatment planning using Cyberknife was based on 4DCT (respiratory phase-binned at Ph 0, 20, 40, 60, 80) + expiration breath-hold CT (CT ebh , approximated Ph50). Standard 3D Cyberknife treatment planning included accounting for target-surrogate geometric deformation during free breathing by a CTV to ITV margin [2], standard dose optimization using 3D dose calculation on CT ebh , and dose delivery at free-breathing using target tracking technology (implantable cardioverter-defibrillator (ICD) lead as a target surrogate) including initial 6D rigid alignment to the spine followed by 3D (translational) target surrogate tracking. Using the original clinical treatment plan and plan QA mode of the TPS complementary dose distributions were calculated for respiratory phase Ph0 (inspiration), Ph20, 40, 60, and 80 following ICD lead tracking-based image registration and treatment beam alignment. CT, reference structures and all doses were imported in 3D Slicer [3] where all complementary CT images were deformably registered to the reference CT ebh . The obtained transformations were applied to the respective doses. Based on the transformed doses a weighted mean dose (wMEAN) was calculated assuming it is a better estimate of delivered dose accounting for free-breathing related variation of patient’s anatomy during treatment compared to the original dose optimized on CT ebh . The workflow to determine wMEAN is shown in Figure 1. In addition, the alternative dose was calculated on the average CT (AVE) calculated from target-centric (ICD-registered) respiratory phase component CTs. Material/Methods: