Room: Track 3
Our Centre collaborated with the Cardiology team to implement non-invasive cardiac radio-ablation for the treatment of ventricular arrhythmia. This technique is novel and, at the time, had not yet been implemented in Canada. Here we discuss the physics considerations for this innovative technique.
Patients underwent scar-CT imaging and electrocardiographic mapping in the cardiology department to identify the myocardial tissue requiring radio-ablation (GTV-equivalent). A 4D treatment-planning CT was acquired with abdominal compression. The PTV expansion was 3 mm. Planning and dose calculations were performed on the average CT to account for heart motion. Plans were created using Elekta Monaco VMAT with 2 - 3 arcs to allow for mid-treatment imaging. The prescription dose was D95%PTV = 2375 cGy in 1 fraction. Target and OAR constraints were established based on literature and TG-101 values. Fluoroscopy was performed immediately before delivery to verify the breathing motion versus the ITV contour. One or two mid-treatment cone beam CTs were acquired to minimize intra-fraction mis-alignments.
To date we have treated 2 patients. The greatest challenge has been the registration between the treatment planning and the scar-CT since the latter is traditionally acquired on a regular diagnostic bed without abdominal compression. Although the PTV volumes were large (180.6cc and 136.9cc), target coverage was met and doses to OARs met the desired constraints. Beam-on time with a flattened beam was between 15 and 30 minutes. Fluoroscopic imaging was found to provide limited value.
We have successfully implemented a non-invasive workflow for stereotactically treating patients with ventricular tachycardia at our centre, a first in Canada. Cardiology was provided a flat tabletop and a compression device for future patients. Our ongoing upgrade to FFF beams will reduce intra-fraction motion and potentially eliminate extra cone-beam CT imaging.