Cardiac stereotactic body radiation therapy for refractory ventricular tachycardia: Impact of cardiac and respiratory movement on the target volume definition

Introduction Cardiac stereotactic body radiation therapy (SBRT) appears to be effective for patients with refractory ventricular tachycardia (VT) by delivering a single ablative radiation dose of 25 Gy to the arrhythmogenic region. Definition of treatment volume is a critical step, integrating combination of cardiac and respiratory motion. The main objective of this study was to evaluate the impact of cardiac and respiratory motion on the definition of target volume. Methods and materials The study presents the targeting data from the first patient enrolled in our institution for SBRT. Treatment planning was performed using different imaging modalities: a respiration-correlated 4D CT, a cardiac-correlated 4D CT, a MRI scan and electrophysiological data from prior catheter ablation. A registration was performed between the different imaging modalities. Respiratory and cardiac motions were quantified in left–right (LR), anteroposterior (AP) and supero-inferior (SI) directions for the target (calcifications) and for the defibrillation lead. The treatment area was delineated using diastolic and systolic cardiac phases of the cardiac-correlated 4D CT, to optimally define a treatment zone accounting for target's displacements related to cardiac motions. Results Target motions amplitude induced by heartbeats were close to those induced by respiration. Respiratory motions of the target were not correlated to that of defibrillation lead (see Table 1 ). The target volume was 15.9 cm3 and 17.7 cm3 for the diastolic and systolic phases, respectively, and 20.7 cm3 when joined together. These differences emphasise the target deformation, and the need of 4D cardiac imaging data for SBRT. Conclusion We showed that optimal definition of the target volume in SBRT requires respiratory and cardiac correlated images. The use of defibrillation lead as a surrogate might result in target localisation inaccuracies, which need to be taken into account in the final planning target volume.