2682 - Dosimetric and Clinical Data from Linac-Based Stereotactic Arrhythmia Radioablation

F. Gregucci¹, J. Ng¹, J. P. S. Knisely¹, J. W. Cheung², G. Thomas², C. F. Liu², L. Muller¹, R. Pennell¹, and S. C. Formenti¹; ¹Department of Radiation Oncology, NewYork-Presbyterian/Weill Cornell Medicine, New York, NY, ²Division of Cardiology, NewYork-Presbytarian/Weill Cornell Medicine, New York, NY

Purpose/Objective(s): Ventricular tachycardia (VT) in patients with structural heart disease is associated with reduced quality of life and poor prognosis. Therapeutic options include medication, anti-tachycardia pacing or shock by implantable cardiac devices and catheter-based ablation of heart arrhythmogenic substrates. STereotactic Arrhythmia Radioablation (STAR) tested in a phase I/II trial by Robinson and colleagues offers a novel approach. Materials/

Methods: Data from a retrospective series of 5 high-risk patients with VT refractory to catheter ablation and medication, treated with STAR are reported from a single referral center. CTV was defined to encompass the arrhythmogenic substrate by a team of a radiation oncologists and treating electrophysiologists, based on clinical and electro-anatomical information derived from CT scan and catheter ablation maps. ITV was added to CTV to compensate for heart and respiratory movement. PTV was then defined by adding an isotropic margin of 2-3 mm to the ITV. Volumetric Modulated Arc Therapy (VMAT) plans were generated, optimized, and delivered using a medical linear accelerator. The prescription dose to the PTV was 25 Gy in 1 fraction.
Results: Mean CTV, ITV and PTV volumes, were 141.1cc, 187.7cc, 298.1cc, respectively. Mean heart volume was 1740.6 cc. All 5 patients completed STAR procedure and treatment. There were no acute treatment-related adverse events. Clinical and treatment-efficacy data are summarized in Table. STAR significantly reduced or abrogated arrythmia at a median time of 24 weeks (range 4-48) post-treatment. Patient n.1 and n.3 showed a remarkable reduction of VT episodes at 4- and 8-weeks post-treatment, respectively. Patients n.2, n.4 and n.5 were free of VT episodes at 6-months post-treatment. At a median follow-up time of 11 months (range 1-19), 2/5 patients are alive (patient n.2 and n.4), both free of VT events at 1-year post-treatment. Patient n.1 died due to complication after cardiac transplantation, patients n.3 due to sepsis and multiorgan failure and patient n.5 due to COVID pneumonia, at 11-, 1- and 5-months post-STAR, respectively.
Conclusion: These data suggest that LINAC-based STAR is a safe and effective treatment option in high-risk patients with VT refractory to catheter ablation and medication. Results from large perspective studies will define optimal patient selection and inform about long-term outcomes. Abstract 2682 – Table 1

Patient	Follow up	Status	Arrhythmia condition pre-STAR	Arrhythmia condition post-STAR
#1	11 months	Deceased	16 treated VT/VF episodes	2 VT episodes within 2 months post treatment
#2	19 months	Alive	5 ICD shocks and 3 catheter ablations	0 VT episodes at 6- and 12-months post-treatment
#3	1 month	Deceased	>30 VT therapies and VT storm	Remarkable reduction of VT episodes at 4 weeks post treatment
#4	12 months	Alive	>30 ICD shocks and VT storm	0 VT episodes at 6- and 12-months post-treatment
#5	6 months	Deceased	27 VT therapies and 107 VT episodes	0 VT episodes at 6 months post treatment