2199 - Stereotactic Body Radiosurgery for Refractory Ventricular Tachycardia: Reporting Efficient Clinic Workflow, Dosimetric Analysis and Patients Reported Clinical Outcomes

Purpose/Objective(s): Noninvasive stereotactic body radiosurgery (SBRS) is emerging as an effective treatment for advanced heart failure patients with refractory ventricular tachycardia (VT) who experience recurrent implantable cardiovascular defibrillator (ICD). Here, we present our SBRS treatment workflow, dose volume metrics, and patient reported clinical outcomes.

Materials/Methods: For five refractory VT patients, SBRS simulation was performed with/without IV contrast-enhanced CT, VacLoc-bag, arms above head, abdominal compression, and 4D-CT scan. Utilizing electroanatomical mapping with a Medtronic Vest tool, target was delineated by an experienced electrophysiologist(s) via AHA heart model. Planning target volume (PTV) includes target plus 3-5 mm isotropic margin: 34.5 ± 33.5 (9.9–93.3) cc. SBRS plans utilized highly non-coplanar partial VMAT geometry, optimal collimators, and couch positions on TrueBeam (6MV-FFF, Acuros-XB) LINAC for a single-dose of 25 Gy (maximum, 31.3 Gy). SBRS plans were optimized for target coverage, conformity, and minimal dose to critical organs including heart–PTV. Pre-treatment CBCT-based IGRT and PerfectPitch couch corrections was used. Patients were monitored for number of VT episodes requiring therapy, including anti-tachycardia pacing and ICD shocks before and after SBRS.

Results: The VT SBRS plans resulted in a conformity index: 1.00 ± 0.03 (0.99–1.05); steep dose gradient: 2.97 ± 0.24 (2.66–3.31) and mean dose to heart–PTV: 2.8 ± 0.9 (1.7–3.7) Gy. Maximum dose to OAR including stomach, small-bowel and ribs were kept low. Patient-specific QA and independent in-house Monte Carlo second check results were 99.1% (2%/2mm gamma criteria) and 1.6%, respectively. CBCT-guided SBRS delivery time was under 20 min including 6.8 ± 1.7 (5.1–9.3) min of radiation beam on time. All patients survived post-SBRS with no adverse effects. Mean follow up interval was 9.9 (3.0–19.8) months. The first patient had >20 events/month; received SBRS targeting the mid-lateral LV wall, significantly reducing VT burden (none) but complicated with phrenic nerve paralysis, which required diaphragmatic plication. After 6 months, the patient experienced a recurrence of VT that necessitated endocardial VT ablation. Second, third, and fifth patients had 10-50 events/month before SBRS, there was a significant reduction in VT burden post-SBRS (0-2 events). Fourth patient did not experience VT but presented with frequent PVCs, which interfered with biventricular (BiV) pacing. Notably, BiV pacing improved from 86 to 89% post-SBRS.

Conclusion: This highly non coplanar SBRS planning and delivery with no clearance issue provided a highly conformal radiosurgical dose distribution for VT with minimal dose to adjacent critical organs. This noninvasive SBRS treatment was feasible, safe, and reasonably effective at reducing VT and PVC burden in advanced heart failure patients and improved their quality of life. Long term follows up result of VT SBRS with a larger cohort is warranted.