Room: Track 3
Purpose: Safe delivery of cardiac radiosurgery for atrial fibrillation (AF) is challenged by complex target motion, cardiac rhythm variability, and target proximity to critical structures. Additionally, complete target dose coverage is crucial for therapeutic benefit. Careful selection of treatment protocol is therefore essential. This work characterizes AF cardiac radiosurgery target motion and target proximity to surrounding structures. These results will help advise optimal treatment technique.
Methods: Five patients with uncontrolled AF and ten healthy volunteers underwent non-contrast MRI. Multiple cardiac-gated, breath-held 2D images were sequentially acquired in three orthogonal planes and interpolated to create 3D images across 18-30 cardiac phases. Treatment targets, defined as the left and right pulmonary vein antra, and critical structures were contoured. Target centroid displacement throughout the cardiac cycle was assessed. Minimum 3D target displacements to critical structures were measured. Free-breathing ,real-time 2D images were also acquired at 4Hz frequency for one-two minute duration. The motion of easily identifiable points within the targets and diaphragm were measured to assess target motion with respiration.
Results: Average 3D displacement of treatment targets due to cardiac contraction in AF participants (4.1±2mm) was marginally smaller than in healthy participants (5.0±1mm) and motion was largest in the medial-lateral direction (3.6±2mm/4.2±2mm medial-lateral, 2.6±1mm/3.7±1mm anterior-posterior, 2.5±1mm/2.8±1mm superior-inferior for AF and healthy participants respectively). The minimum displacement between the aorta and left and right treatment targets was on average 2mm and 12mm respectively. The esophagus was within 1mm of the left target for 40% of participants and on average 6mm from the right target. Target motion due to respiration in the superior-inferior direction (13±4mm) was smaller than diaphragm motion (23±5mm).
Conclusion: AF cardiac radiosurgery target motion and relative displacement was characterized. The combination of target motion magnitude and relative displacement to critical structures highlights the importance of suitable motion compensation techniques for optimal treatments.
Funding Support, Disclosures, and Conflict of Interest: This study was funded by the Auckland Academic Health Alliance (AAHA), NZ.