4D robust evaluation for the intensity-modulated-proton-radiotherapy plans for patients with ventricular tachycardia based on cardiopulmonary motion characteristics.

BACKGROUND

Clinical trials and case reports have demonstrated that radiotherapy effectively reduces the frequency of ventricular tachycardia (VT) events. Given the sensitive anatomy of the treatment target, it is important to minimize the normal tissue dose while optimizing the target dose. This retrospective study investigated the optimal treatment planning strategy utilizing proton beams for VT patients to mitigate the effect of both cardiac and respiratory motion.

METHODS

Twelve patients with respiratory-related 4DCT data and six patients with cardiac 4DCT data were enrolled in this study. The left ventricular wall was segmented into four regions (Anterior, Inferior, Lateral and Septal) according to Milo's delineation guidelines to simulate various CTVs. Single-field plans with five different kinds of beam angle and multi-field plans were created to identify the optimal angle.

RESULTS

The selection of beam angles significantly affected target coverage. The dose uncertainty due to respiratory motion was found to be greater than that of the heartbeat based on the 4D dynamic dose evaluation. Multi-field plans provided better protection for the heart and lungs but showed limitations in ensuring sufficient target coverage under respiratory motion, particularly for Inferior and Lateral targets.

CONCLUSION

For optimal dose delivery (defined as achieving robust target coverage), a multiple-field plan with beam angles of 60° (targets A and I), 90° (targets L) and 30° (targets S) as the primary field is recommended. Patient-specific 4D dynamic evaluations are of great importance to ensure the treatment's safety and effectiveness.

ABBREVIATIONS: VT, ventricular tachycardia; r4DCT, respiratory-related 4DCT; c4DCT, cardiac 4DCT; VF, ventricular fibrillation; ICD, implantable cardioverter defibrillators; SART, stereotactic ablative radiotherapy; CTV, clinical target volume; ICTV, internal clinical target volume; RBE, relative biological effectiveness; 4DDD, 4D dynamic dose; PBS, pencil beam scanning; DIR, deformable image registration; WEL, water-equivalent path length; OARs, organs at risk; DIR, deformable Image Registration; HI, homogeneity index; CI, conformability index; rCT, repeat CT; UHDR, ultra-high dose-rate; Lung-L, left lung; Lung-R, right lung; Lung-All, left lung + right lung.