Room: Track 3
Purpose: To develop a respiratory gating workflow for the treatment of ventricular tachycardia (VT) with cardiac radioablation.
Methods: VT targets were identified using a patented noninvasive mapping system (Vektor Medical, Carlsbad, CA) for a cohort of 5 patients. The model-based algorithm used a standard 12-lead electrocardiogram (ECG) captured during VT to identify the target as a 3D heatmap. This information was combined with scar imaging to create the final target on a high-resolution cardiac computed tomography (CT) image. For radiotherapy simulation, the heart was paced at 100 beats-per-minute (BPM) to stabilize and reduce cardiac cycle motion, and both 4-dimensional CT (4DCT) and expiration breath hold (EBH) scans were acquired. After registration with the cardiac CT, the VT internal target volume (ITV) was contoured on the average CT of the 4DCT expiration phases. Using the expiration phases and EBH image, the locus of implantable cardiac defibrillator (ICD) lead positions were contoured at expiration to create a structure representing all possible ICD lead positions during expiration. Treatment planning was performed using Eclipse and treatments were delivered using a TrueBeam™ linear accelerator (both Varian Medical Systems, Palo Alto, CA). Following cone beam CT imaging for soft tissue alignment, fluoroscopic imaging was used to verify ICD lead locations during expiration and that the respiratory gating window was set correctly for treatment.
Results: VT targets were identified for all patients, including a variety of morphologies and locations. Pacing the heart at 100 BPM resulted in decreased ICD lead motion, when compared to no pacing. Using fluoroscopic imaging to match the ICD leads to a structure representing all possible ICD lead positions during expiration was possible for all cases.
Conclusion: A robust respiratory management workflow using ICD leads and fluoroscopic imaging allowed for gated treatment of reduced ITV volumes for cardiac radioablation of VT.