Towards cardiac and respiratory motion management in cardiac radioablation

Cardiac radioablation (CR) is an emerging treatment for ventricular tachycardia that uses radiation to treat the region in the heart responsible for this abnormal heart rhythm. Delivering CR is challenging because the heart moves during both patient breathing and cardiac beating. These motions introduce uncertainties into treatment planning and delivery, requiring an expansion of the treatment volume, which can increase radiation exposure to nearby healthy tissues. This thesis explores methods for managing cardiac- and respiratory-induced motions in CR. First, margins to account for cardiac and respiratory motions in CR are investigated and different methods of computing these margins are compared. Dosimetric margins can be calculated using a margin formula. Further, the conservative approach of accounting for the amplitude of cardiorespiratory motion can overestimate the dosimetric margin which may result in excess irradiation of healthy tissues. Second, the ability to reduce breathing-induced motion using an abdominal compression (AC) belt is assessed. By assessing patient motions under both AC and free breathing (FB) conditions, it was found that most CR patients had reduced respiratory motions using AC to restrict breathing. Third, since most CR patients have one or more implanted cardiac leads due to the presence of an implanted defibrillator, this thesis examines the use of these leads or the diaphragm as surrogates for active respiratory motion management. The respiratory motion of all combinations of implanted cardiac leads and the diaphragm are moderately to strongly correlated after accounting for phase shifts between motion traces. These phase shifts should be carefully considered to ensure patient safety during respiratory tracking or gating during CR. Finally, the use of three implanted cardiac leads is explored to model the translational and rotational motion of the heart through respiration. This work quantifies the heart’s rotation through respiration and highlights its importance for real-time motion monitoring. For each patient dataset, modelling translations and rotations improved the accuracy of respiratory motion localization for pseudo-targets on the lateral wall of the left ventricle. Together, this thesis presents novel contributions to managing cardiac and respiratory motions in cardiac radioablation, with the aim of improving treatment precision and patient outcomes.