Researchers are gathering information on the safety and effectiveness of proton radiation therapy in reducing the number of ventricular tachycardia (VT) episodes in subjects who continue to experience VT despite treatment with an implantable cardioverter defibrillator (ICD) and undergoing a previous catheter ablation.

Proton therapy has been approved by the U.S. Food and Drug Administration (FDA) for cancer patients, including tumors in the heart, but not for treating heart rhythm disorders. The use of proton radiation therapy to treat heart rhythm disorders including VT and ventricular fibrillation (VF) is new and investigational; however, the FDA has approved proton therapy to treat abnormal rhythm disorders for this study. The development of a proton radiation therapy approach could be of substantial value in providing alternative therapy to either drug therapy or catheter-based ablation. With appropriate development, this therapy may be successful in the primary or secondary elimination of arrhythmias.

Participants will be followed at 1 and 2 weeks, 1, 3, 6, 12 and 24-month intervals following treatment throughout the trial.

Participant involvement will last approximately two years from the time of the proton radiation therapy procedure or until the last subject enrolled completes a 24 month follow-up.

Inclusion Criteria:

1. Prior myocardial infarction, or non-ischemic disease, resulting in myocardial dysfunction
2. EF <50%
3. An implanted ICD device as secondary prevention for monomorphic VT/VF (MMVT/MMVF). This includes patients who receive a device for primary prevention and then have recurrent sustained monomorphic VT or VF.
4. Have failed a prior catheter-based ablation for VT/VF after device implantation or have a contraindication to repeat ablation and have failed reasonable drug options over the 9 months prior to consideration of particle therapy.
5. Repeat ablation from an epicardial venue in the absence of prior cardiac surgery, or where such an ablation is felt to be inappropriate in the view of the PI.
6. Electrocardiographic documentation of 2 additional episodes of recurrent, sustained monomorphic ventricular tachycardia (MMVT) and/or PVC induced VT or VF that are terminated by ATP or ICD shocks (by device interrogation) over the past 9 months, since the sentinel ablation (see criteria #4). Also included, incessant VT that does not fall within device parameters for activation of ATP or shock delivery or is refractory to medication titration.
7. Age <=80 years.

Exclusion Criteria:

1. VT in the absence of cardiomyopathy.
2. Reversible causes of VT including thyroid disorders, acute alcohol intoxication, recent major surgical procedures, trauma, or VT clearly produced by recurrent ischemia.
3. Multiple (e.g.>3) clinical VT morphologies that are thought to originate from widely disparate RV or LV areas.
4. Recent cardiac events including MI, PCI, or valve or bypass surgery in the preceding 3 months, or anticipated in the next 3 months.
5. Hypertrophic obstructive cardiomyopathy (HOCM) >Class IV
6. Progressive Class IV angina, or Class IV CHF (including past, or planned heart transplantation).
7. Heritable arrhythmias or increased risk for torsade de pointes with Class I or III drugs.
8. Prior surgical interventions for VT such as an encircling ventriculotomy procedure.
9. Contraindication to appropriate anti-coagulation therapy after ablation.
10. Renal failure requiring dialysis.
11. Prior therapeutic radiation therapy to the left chest that would preclude safe ablation of the cardiac target in the judgement of the radiation oncologist.
12. Medical conditions limiting expected survival <1 year.
13. Women of child bearing potential (unless post-menopausal or surgically sterile)
14. Participation in any other clinical mortality trial (participation in other non-mortality trials should be reviewed with the clinical trial management center)
15. Unable to give informed consent.