Ventricular tachycardia (VT) is a potentially deadly condition, common in patients with structural heart disease or dilated cardiomyopathy. VTpatients are currently treated with anti-arrhythmic drugs, implanted cardioverter defibrillators or invasive catheter ablation (CA) but the overall success rate of this techniqueis still suboptimal.

One of the main reasons is an anatomically inaccessible location of VT's origin (within the mid-wall of the myocardium, on the epicardial site or adjacent to critical structures). Moreover, repeated invasive ablation, technical difficulties or patient comorbidities can lead to non-eligibility for CA. Accordingly, a rationale exists to adopt more effective and less invasive therapies.

A promising novel non-invasive treatment option for refractory VT is stereotactic arrhythmia radio-ablation (STAR), originally born for cancer treatment, which consists in the application of high-energy photons in a single 25 Gy dose to limited areas of the ventricles, also to those inaccessible for CA, recognized through non-invasive surface ECG-mapping as the origin of VT. Preliminary small case series described good tolerance and improved VT burden during follow-up.

Due to the encouraging physical and biological characteristics of protons and carbon ions, the dose to surrounding healthy tissues could potentially be better spared in comparison with photons. Especially, the cardiac healthy sub-structures might benefit from the use of particle beams instead of photons. On the other hand, due to range uncertainties affecting particle beams, delivering an ideal radiation treatment with heavy ions to fast-moving targets such as the heart, is more complex. So far, the feasibility and the safety of cardiac radiotherapy with protons and heavy ions have only been evaluated in animal models and recently in the first in man case managed by the collaboration between CNAO and San Matteo Cardiology Department in a patient treated with compassionate aim.

To date, feasibility and safety data showing potential advantages of particles over photon therapy in dose distributions are missing.

Therefore, we propose a study aimed to compare different radiation therapy treatment modalities (photons vs. particle therapy: protons and carbon ions) simulating the RT treatment of ventricular arrhythmias on real patients candidates to invasive catheter ablation treatment.

STAR with photons was first reported in 2013 and an increasingly number of case reports and case series have been published ever since, showing an acceptable safety profile and promising efficacy.

Decreasing the dose to the surrounding healthy heart tissues is expected to be very advantageous for patients.

Particle therapy based on its dosimetric physical selectivity compared to SBRT (Stereotactic Body Radiotherapy) with photons might have the potential to both lower off-target doses and lower risk of possible side effects.

Inclusion Criteria:

• Recurrent VT with clinical indication to receive catheter ablation
• Written informed consent
• Patient's ability to understand the characteristics and consequences of the clinical study
• Invasive mapping data

Exclusion Criteria:

• Allergy to iodinated contrast media
• Pregnancy and breastfeeding
• Younger than 18 years

Thirty patients suffering recurrent VT with clinical indication to receive invasive catheter ablation will be included in the study