Optimizing Beam Angles through 4D Robust Evaluation to Counteract Cardiopulmonary Motion In Cardiac Proton Therapy
Abstract
Purpose
Radiotherapy has emerged as an effective noninvasive treatment for refractory ventricular tachycardia (VT). Given the high sensitivity of cardiac structures, proton therapy offers potential dosimetric advantages, but its robustness under cardiopulmonary motion remains uncertain. This study aimed to evaluate the impact of respiratory and cardiac motion on proton dose delivery and to determine optimal beam configurations for VT treatment planning.
Methods
Respiratory 4DCT (r4DCT) data from 12 patients and cardiac 4DCT (c4DCT) data from 6 patients were retrospectively analyzed. The left ventricle was divided into four regions (anterior, inferior, lateral, septal) to simulate different target locations. Single-field plans with multiple beam angles and three-field plans were generated using robust optimization (±3.5% range and 5 mm setup uncertainty) and evaluated via 4D dynamic dose(4DDD) accumulation. Dose-volume metrics (V25, D95%, HI, CI) were compared to quantify motion effects and plan robustness.
Results
Beam angle strongly influenced target coverage and organ sparing. Respiratory motion induced larger dose variations than cardiac motion. Optimal beam angles were 60° for anterior/inferior, 90° for lateral, and 30° for septal targets. Multi-field plans improved heart and lung protection but exhibited slightly reduced target robustness, particularly for inferior and lateral walls. Inter-fractional analysis confirmed greater reproducibility for anterior and septal targets. The 4DDD results demonstrated that respiratory-induced dose distortion exceeded cardiac motion effects across all configurations.
Conclusion
Respiratory motion contributes more significantly to proton dose uncertainty than cardiac pulsation in VT treatment. Multi-field plans with main angles of 60°, 60°, 90°, and 30° for the anterior, inferior, lateral, and septal targets, respectively, offer optimal balance between target coverage and normal tissue protection. Patient-specific 4D robust evaluation is essential to ensure treatment safety and precision.