• Patients with structural heart disease (SHD) of any etiology (ischemic, non-ischemic, congenital corrected or uncorrected)

• Implanted implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy-defibrillator (CRT-D)

• Prior ≥1 catheter ablation procedure for VT due to SHD of them the last one performed in the expert center and employed:

⁃ 1 all meaningful mapping/ablation approaches (endocardial/epicardial access to left / right ventricular substrate as possible or appropriate) 3.2 precise electroanatomical mapping of the arrhythmogenic substrate in anticipation of future radiosurgery 3.3 additional mapping of structures used for precise image integration (aortic arch, left main ostium, right ventricular endocardial surface)

• VT recurrence after the last catheter ablation fulfilling all criteria as follows:

⁃ 1 clinically relevant and requiring further intervention 4.2 compatible with the previously characterized arrhythmogenic substrate 4.3 occurred on stable antiarrhythmic medication (mostly amiodarone) unless contraindicated 4.4 reversible cause excluded

• Signed an Institutional Review Board (IRB)-approved written informed consent