Treatment Planning Considerations for Robotic Guided Cardiac Radiosurgery for Atrial Fibrillation

Abstract

PurposeRobotic guided stereotactic radiosurgery has recently been investigated for the treatment of atrial fibrillation (AF). Before moving into human treatments, multiple implications for treatment planning given a potential target tracking approach have to be considered. Materials & MethodsTheoretical AF radiosurgery treatment plans for twenty-four patients were generated for baseline comparison. Eighteen patients were investigated under ideal tracking conditions, twelve patients under regional dose rate (RDR = applied dose over a certain time window) optimized conditions (beam delivery sequence sorting according to regional beam targeting), four patients under ultrasound tracking conditions (beam block of the ultrasound probe) and four patients with temporary single fiducial tracking conditions (differential surrogate-to-target respiratory and cardiac motion). ResultsWith currently known guidelines on dose limitations of critical structures, treatment planning for AF radiosurgery with 25 Gy under ideal tracking conditions with a 3 mm safety margin may only be feasible in less than 40% of the patients due to the unfavorable esophagus and bronchial tree location relative to the left atrial antrum (target area). Beam delivery sequence sorting showed a large increase in RDR coverage (% of voxels having a larger dose rate for a given time window) of 10.8-92.4% (median, 38.0%) for a 40-50 min time window, which may be significant for non-malignant targets. For ultrasound tracking, blocking beams through the ultrasound probe was found to have no visible impact on plan quality given previous optimal ultrasound window estimation for the planning CT. For fiducial tracking in the right atrial septum, the differential motion may reduce target coverage by up to -24.9% which could be reduced to a median of -0.8% (maximum, -12.0%) by using 4D dose optimization. The cardiac motion was also found to have an impact on the dose distribution, at the anterior left atrial wall; however, the results need to be verified.ConclusionRobotic AF radiosurgery with 25 Gy may be feasible in a subgroup of patients under ideal tracking conditions. Ultrasound tracking was found to have the lowest impact on treatment planning and given its real-time imaging capability should be considered for AF robotic radiosurgery. Nevertheless, advanced treatment planning using RDR or 4D respiratory and cardiac dose optimization may be still advised despite using ideal tracking methods.

Radiosurgery for ventricular tachycardia: preclinical and clinical evidence and study design for a German multi-center multi-platform feasibility trial (RAVENTA)

“…Finally, we added initial technical, pre-clinical, and clinical manuscripts not covered by the search based on our own experience in cardiac radiosurgery in the past 12 years. Evidence was finally extracted from the remaining 42 manuscripts, which include reports on two clinical trials [22,23], two clinical case series [24,25], eight case reports [19,20,[26][27][28][29][30][31], eight preclinical studies [18,[32][33][34][35][36][37][38][39], fourteen technical studies [40][41][42][43][44][45][46][47][48][49][50][51][52][53], and eight reviews or opinions [7,[54][55][56][57][58][59][60].…”

“…There are already various studies published for catheter ablation which investigated the cardiac and respiratory motion of cardiac substructures to obtain a better registration between electrophysiological measurements and pre-procedural imaging [61]. Additionally, for RA/CRS, two studies investigated the motion of the left atrium and the pulmonary veins, and found highly variable respiratory and cardiac motion ranges and also differential motion between left, right, anterior, and posterior pulmonary veins [45,47]. However, with most modern radiotherapy equipment, the major source of motion (namely originating from respiration) can be compensated to a high degree of accuracy [62], while cardiac contraction motion seems to have a limited impact on the dose distribution [53].…”

Investigation of the XCAT phantom as a validation tool in cardiac MRI tracking algorithms

“…For AF treatment plans, margin sizes less than 3-5 mm may be within acceptable limits [12], [33]. Therefore, the tracking error of the tracking algorithm in our study (3.7 ± 0.6 mm) could contribute to the proof-of-concept for non-invasive cardiac radiosurgery under real-time MRI guidance.…”

“…Although not detailed in this work, we expect that this validation method could be used for a range of tracking validations and treatment planning studies, especially when 4D patient data is difficult to acquire. In fact, imaging data comprising cardiac and respiratory motion alike would have been helpful in previous treatment planning studies for cardiac radiosurgery [12,33]. The analysis in this work was made possible by validation through quantitative measures provided by the XCAT digital phantom for the first time.…”

Swine Atrioventricular Node Ablation Using Stereotactic Radiosurgery: Methods and In Vivo Feasibility Investigation for Catheter‐Free Ablation of Cardiac Arrhythmias

“…A study recently analyzed treatment planning for pulmonary vein isolation using CyberKnife in patients with atrial fibrillation and showed that CyberKnife could be used in up to 40% of patients for atrial fibrillation ablation. It is thought that with improved motion‐tracking systems and SRS technology, a larger percentage of patients can be eligible for the procedure.…”