Stereotactic arrhythmia radioablation for ventricular tachycardia in S-ICD patients: mission impossible?

Lena Kästner (Mannheim)1, J. Xie (Lübeck)2, H. Fanslau (Mannheim)1, K. Siebenlist (Mannheim)1, M. Eckl (Mannheim)1, J. Fleckenstein (Mannheim)1, D. Bürgy (Mannheim)1, M. Kuru (Mannheim)3, J. Kuschyk (Mannheim)4, D. Dürschmied (Mannheim)4, D. Krug (Kiel)5, F. Giordano (Mannheim)1, A. Schweikard (Lübeck)2, O. Blanck (Kiel)5, J. Boda-Heggemann (Mannheim)1, B. Rudic (Mannheim)4

1Universitätsklinikum Mannheim Klinik für Strahlentherapie und Radioonkologie Mannheim, Deutschland; 2Universitätsklinikum Schleswig-Holstein Lübeck, Deutschland; 3Universitätsklinikum Mannheim Klinik für Radiologie und Nuklearmedizin Mannheim, Deutschland; 4Universitätsklinikum Mannheim I. Medizinische Klinik Mannheim, Deutschland; 5Universitätsklinikum Schleswig-Holstein Klinik für Strahlentherapie Kiel, Deutschland



The subcutaneous ICD (S-ICD) is increasingly adopted in the primary and secondary prevention of sudden cardiac death. S-ICD carriers with structural heart disease are at an increased risk of monomorphic ventricular tachycardia (VT). Stereotactic arrhythmia radioablation (STAR) of ventricular tachycardias is a novel method for treatment of therapy-refractory VT. Strict dose constraints are necessary for STAR treatment to avoid radiation-induced damage to electronic devices such as the ICD. Due to its specific placement in the left axillary region and proximity to left lateral and apical myocardium, the presence of an S-ICD can impose technical barriers for performing STAR. Currently, insufficient data exists about feasibility of STAR treatment in patients with an S-ICD.



To assess the feasibility and quality of treatment plans for STAR in S-ICD patients with an offline planning study.



Previously acquired clinical and cardiac computed tomography (CT) data of 10 S-ICD patients was retrospectively analyzed. Individual CT scans were semi-automatically segmented with the in-house software CARDIO-RT according to the standardized AHA 17-segment model. Cardiac substructures, thoracic organs at risk and Planning Target volumes (PTVs) for segments (S) 8, 11 and 17 representing the septal, lateral and apical left-ventricular regions were contoured assuming region of interest for delivering STAR. Treatment plans were calculated for each patient and each segment with a PTV dose of 25 Gy according to the RAVENTA (RAdioablation for VENtricular Tachycardia) study protocol with sparing of the S-ICD from the primary radiotherapy beam (recommended Dmax 1 Gy, optimum <0.5 Gy).



Cardiac CT data of ten patients (70% male), mean age 68 ± 7 years with previously implanted S-ICD were retrospectively used for simulated STAR planning. Mean ejection fraction was 34 ± 12% and left ventricular end-diastolic dimension 54 ± 8 mm. Ischemic heart disease was present in 80% of cases. 

Most plans resulted in successful sparing of the S-ICD from the primary beam with doses below the recommended constraint of maximal 1 Gy. A single case with a distance between PTV in S17 and S-ICD below 2 cm, resulted in an S-ICD dose of 1.7 Gy, which would have been a major RAVENTA protocol deviation and could potentially induce a device upset.

Maximum dose (Dmax) for the S-ICD was 0.37 ± 0.07 Gy in S8, 0.53 ± 0.44 Gy in S11, and 0.4 ± 0.09 Gy in S17 (P = 0.3). PTV coverage and dose constraints to organs-at-risk (lungs, esophagus, aorta, thoracic wall, skin, whole heart-PTV, spinal cord and esophagus) were all acceptable. However, in some cases minor protocol deviation occurred regarding PTV dose conformality, coverage and hot spots for lateral segment 11. This occurred specifically in case of cardiomegaly and if the target-S-ICD distance was below 4 cm. 



S-ICD Dmax was slightly higher in the lateral segment S11 and resulted in major deviation for one case with cardiomegaly and a distance below 2 cm. S-ICD doses were comparable in all three planning segments for all remaining cases. The presence of an S-ICD did not impede potential application of STAR for VT treatment in most cases. Rare anatomic situations with target-S-ICD distance below 2 cm can lead to major ICD dose deviations and potential risks of radiotherapy-induced device upsets. 

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