Inclusion Criteria:  ECOG 0-2 Age 18 years or older Diagnosis of recurrent sustained monomorphic VT (MMVT) in the setting of structural heart disease. ICD placement and at least two (2) episodes of recurrencerecurrent sustained MMVT that are terminated by anti-tachycardia pacing (ATP) or ICD shocks confirmed by device interrogation in the preceding 3 months, since the last VT ablation procedure in subjected who have failed catheter ablation. Failed at least 1 anti-arrhythmic medication (not including beta-blockers) as evidenced by persistent VT (including amiodarone and/or sotalol) At least 1 attempted catheter ablation procedure with voltage and/or activation 3D mapping. For patients with ischemic cardiomyopathy this would include failure of at least one endocardial ablation performed at an experienced center. For patients with non-ischemic cardiomyopathy, both endocardial and epicardial ablation should have been attempted unless epicardial ablation/mapping is not feasible (e.g. patient tolerance, deemed futile by EP, prior cardiac surgery). Patients are eligible regardless of past or present oncologic history (however, please refer to exclusion criterion #1 below, regarding life-expectancy of at least 12 months in the absence of VT)  Exclusion Criteria:  Unlikely to live at least 12 months in the absence of VT, as assessed by physicians Heart failure dependent on ionotropes Left ventricular assist device Polymorphic VT Ventricular fibrillation 5 or more VT morphologies during stimulation testing suggestive of more than one arrhythmogenic substrate Prior radiation treatment to the chest for any reason Last invasive catheter ablation attempt <2 weeks Lack of ICD data in preceding 3 months Unable/unwilling to provide informed consent Idiopathic VT Women who are pregnant Heart transplant Active ischemia or other reversible causes of VT Active non-cardiovascular illness or systemic infection Cardiogenic shock Presence of incessant VT that is hemodynamically unstable Acute heart failure exacerbation Revascularization in the past 30 days Left ventricular ejection fraction <15% Scar tissue exceeding 80cc in volume planning treatment volume (PTV) ≥300cc.