Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation Purpose Cardiac radioablation has evolved as a potential treatment modality for therapy-refractory ventricular tachycardia. To standardize cardiac radioablation treatments, promote accurate communication and target identification, and to assess toxicity, robust and reproducible methods for angulation and cardiac segmentation are paramount. In this study, we developed and evaluated a workflow for semi-automated angulation and segmentation according to the American Heart Association (AHA) 17-segment model. Methods and materials The workflow for semi-automated angulation and segmentation of the planning-CT was based on an in-house developed tool requiring placement of only 4 point-markers and a rotation matrix. For angulation, 2 markers defining the cardiac long-axis were placed: at the cardiac apex and at the center of the mitral valve (figure A). A rotation matrix was derived that angulates the CT-volume, resulting in the cardiac short axis (figure B). Segmentation was subsequently performed based on marking the two left ventricular hinge points (figure BC). To evaluate reproducibility, 5 observers independently placed markers in planning-CTs of 6 patients. Results The Root-Mean-Square of the standard deviation for the angulation and segmentation marker positions were all below 0.52cm. The 17-segments were subsequently generated and compared between the observers resulting in a median dice coefficient of 0.8 [0.70;0.87] and a median of the mean Hausdorff distance of 0.09cm [0.05;0.17]. Figure D shows the heat maps of two illustrative segments indicating the percentage agreement per voxel between the 5 observers. The interquartile ranges of Euler angles α and β, determined by the angulation markers, was less than 30 for all patients except one. For the γ angle, determined by the hinge point markers, the interquartile range was up to 120. Conclusion In this study, a workflow for cardiac radioablation is presented that enables reproducible semi-automatic cardiac angulation and segmentation of the planning-CT according to the AHA 17-segment model. This workflow can be easily implemented and be used to promote communication between radiation oncology and cardiology, enables cardiology-oriented targeting and permits focused toxicity evaluations.
Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation grant to dr. P.G. Postema, MD PhD Background Stereotactic arrhythmia radiotherapy (STAR) has evolved as promising bail-out treatment in patients with therapy-refractory ventricular tachycardia (VT). The mechanism of action of STAR in preventing VT has yet to be elucidated and further understanding could improve this technique in the future. Preclinical studies reported an increase in conduction velocity and consequently a decrease in conduction intervals on electrocardiograms (ECGs) within the first months after STAR, although this has not yet been evaluated in detail in prospective studies. Purpose To evaluate the early effects of STAR on ventricular conduction as electrocardiographically assessed. Methods The STARNL-1 was a prospective, monocenter, pre-post intervention study. Six patients with VT recurrences despite optimal doses of anti-arrhythmic drugs (AADs), after one or more unsuccessful catheter ablation(s), were considered therapy-refractory. Patients were treated with a single fraction of 25 Gy. ECG evaluation included ECGs recorded pre-therapy, at 3 hours, 12 hours, 24 hours, 1 month, and 3 months after therapy. For an additional assessment, only patients in whom AADs remained unchanged up to 3 months after STAR were selected. QRS duration and QT interval were measured by a single observer using digital callipers. Four consecutive beats were used to measure and calculate a mean QRS duration and QT interval per ECG. This study was not powered to evaluate for significant changes in ECG parameters. Results All patients were male, all suffered from ischaemic cardiomyopathy, and all completed 3-month follow-up. One patient presented with atrial fibrillation on ECG recordings, and three patients with a paced rhythm. Four patients (66.7%) were selected for an additional assessment, two patients (P1 and P2, 33.3%) underwent changes in AAD dose and were therefore excluded. Figure 1 shows a line graph of the QRS duration and QTc interval of all STARNL-1 patients during 3-month follow-up. As can be appreciated from Figure 1, QRS duration and QTc interval did not appear to be altered between pre-therapy and 3 months after therapy. When excluding P1 and P2, QRS duration and QTc interval also did not appear to be altered between pre-therapy and 3 months after therapy. Conclusion(s) STAR for VT does not appear to alter QRS duration and QTc interval within the first 3 months after therapy.
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