Noninvasive Cardiac Radioablation for Ventricular Tachycardia Refractory to Medication and Catheter Ablation

Inclusion Criteria: * Patients must be ≥ 18 years old. * Patients must have documented sustained monomorphic VT by 12-lead ECG or intracardiac ICD interrogation. * Minimum VT burden: 4 or more documented VT episodes (including sustained VT, ICD anti-tachycardia pacing \[ATP\], or ICD shock) in the 5 months preceding enrollment on this trial. Patients must have at least two episodes of electrocardiographically documented symptomatic, recurrent, sustained monomorphic VT in the 3 months prior to enrollment * \*ATP and appropriate ICD shock are acceptable surrogates for VT-associated symptoms * Patients must have an ICD. * Patients must have ischemic or non-ischemic cardiomyopathy previously diagnosed with LVEF ≤ 35%. * Patients must have received at least one antiarrhythmic medication (i.e. amiodarone, sotalol, mexiletine) without control of symptoms or with poor toleration. AND Patients must have undergone at least one catheter-ablation procedure (or have a contraindication to catheter-ablation) or have VT arising from an inaccessible location. * Contra-indications to endocardial catheter ablation procedure include dual aortic and mitral mechanical valves, active left ventricular thrombus, and anesthesia intolerance. * Contra-indications to epicardial catheter ablation include prior cardiac surgery or anesthesia intolerance. * Patients with ischemic cardiomyopathy should have failed at least one endocardial ablation performed at an academic center. * Patients with non-ischemic cardiomyopathy should have failed both epicardial and endocardial ablations, unless epicardial mapping/ablation is not feasible. * Ability to understand and willingness to sign an IRB approved informed consent document (legally authorized representatives are not permissible). * An independent EP cardiologist must confirm that each study participant has met the study entrance criteria, has failed conventional therapies, and has frequent recurrent VT episodes that warrant further rhythm management. Exclusion Criteria: * Patients who have received any prior radiotherapy to the internal organs of the thorax or upper abdomen (with treatment field extending superior to L1 vertebral body) at any time in the past are excluded. * Patients found to have multiple scars on electrocardiographic imaging where the source of reentrant focus is unclear despite positron emission tomography (PET)/magnetic resonance imaging (MRI) are excluded. * Patients who have congestive heart failure on inotropes (NYHA class 4B) or left-ventricular assist device are excluded. * Patients felt to be unlikely to live 12 months in the absence of VT are excluded. * Patients with polymorphic VT or ventricular fibrillation, \>3 distinct clinical VT morphologies on ICD interrogation, or \>5 induced VT morphologies during noninvasive testing are excluded. * Patients with multiple, spatially separate target substrates (targets with presumed inclusion of nonadjacent ventricular segments) deemed unsafe to treat with CRA by the treating physician will be excluded. * Patients with incessant VT that is hemodynamically unstable are excluded. * Patients in VT storm are excluded. * Patients must not be pregnant and must have a negative pregnancy test within 14 days of study entry if they are females of childbearing age.