Proton Beam Therapy Shows Promise as Noninvasive Treatment for Refractory Ventricular Tachycardia
Key Insights
A first-in-human study demonstrated that proton beam therapy (search), a cancer treatment, successfully reduced ventricular tachycardia (search) events by 79% in seven patients who had failed conventional treatments.
The noninvasive procedure showed no treatment-related toxicities during a median follow-up of 514 days, with patients experiencing less frequent and less severe VT episodes.
Researchers delivered a single 30 Gy dose of intensity-modulated proton therapy to target VT substrates while sparing surrounding cardiac and noncardiac structures.
A groundbreaking first-in-human study has demonstrated that proton beam therapy (search), traditionally used for cancer treatment, can significantly reduce ventricular tachycardia (search) episodes in patients with refractory arrhythmias who have exhausted conventional treatment options. The research, presented at Heart Rhythm 2026 and published simultaneously in HeartRhythm, offers new hope for patients with life-threatening arrhythmias.
Novel Approach to Refractory Arrhythmias
The study, led by Konstantinos C. Siontis, MD, a cardiologist and professor of medicine at Mayo Clinic in Rochester, Minnesota, treated seven patients with ventricular tachycardia (search) refractory to antiarrhythmic drugs and catheter ablation using a single fraction of 30 Gy intensity-modulated proton therapy.
"There are certain limitations and for the most part suboptimal outcomes for some of the patients [with ventricular tachycardia (search)] that we treat with catheter ablation, especially those with nonischemic cardiomyopathy (search)," Siontis explained. "So the idea came that a noninvasive external beam approach could avoid some of those limitations of anatomic locations where the catheters have difficulty reaching, or of the extensive procedures that require a lot of anesthesia and invasive approaches."
Significant Reduction in VT Events
The study enrolled seven patients with a mean age of 68 years, six of whom were male. Four patients had nonischemic cardiomyopathy (search), one had ischemic cardiomyopathy (search), and two had mixed disease. The median left ventricular ejection fraction at baseline was 26%. Five patients had undergone two or more catheter ablations previously, and six were treated with amiodarone with or without mexiletine before proton beam therapy (search).
During a median follow-up of 514 days, the rate of ventricular tachycardia (search) events decreased dramatically from 7.24 per patient-month in the 3 months before the procedure to 1.52 per patient-month during follow-up, representing a 79% reduction in VT burden.
The median target volume was 17 cm³, and a median of 4% of nontarget myocardium (search) received 20 Gy radiation or more. Importantly, researchers found no definite or probable treatment-related serious adverse events, and left ventricular ejection fraction remained stable, with median LVEF at 26% at baseline and 25% at the end of follow-up.
Advanced Treatment Planning and Safety Profile
The proton beam therapy (search) utilized the Probeat-V Proton Beam Therapy System, with treatment planning based on information from cardiac imaging, ECG, and electrophysiologic studies. All patients underwent late gadolinium-enhanced MRI, supplemented by echocardiography and, when available, nuclear perfusion, CT, and voltage mapping to define the substrate.
"The radiation modality is a charged particle which is emitted into the heart tissue, or whatever the target might be, with a higher accuracy compared to the photons," Siontis noted. "There's a biophysical property of the protons that allows them to be targeted into the area we want to ablate while minimizing the radiation to the surrounding tissue."
The treatment planning approach carefully outlined all nearby organs at risk, including the esophagus, trachea, lungs, spinal cord, and nontarget left ventricular myocardium (search), to spare them excessive radiation exposure during the procedure.
Clinical Outcomes and Treatment Effects
Six of the seven patients experienced at least one VT event during follow-up, but the character of these episodes changed significantly. Of the 152 sustained VT events in the 3 months prior to radiotherapy, 6.6% were treated with ICD shock, 82.2% with antitachycardia pacing, and 11.2% were monitored. In the 17.1 months after treatment, there were 162 VT events, with 6.8% treated with shock, 91.3% with antitachycardia pacing, and 1.9% monitored.
"The VT was very challenging and all of these patients had failed everything else that we'd done for them," Siontis emphasized. "They did have recurrences, but what is important to note and emphasize is that the burden of VT and the phenotype of VT improved significantly where, in most of the patients, VT became occasionally asymptomatic and ATP-terminated as opposed to having shocks and having a significant impact on their quality of life."
Interestingly, the treatment effect was not immediate in some patients, suggesting that the mechanism of action may involve the induction of progressive necrosis and apoptosis in cardiac tissue. At the end of 2 years, three patients had died and two had undergone heart transplantation, outcomes that would be expected given the advanced cardiomyopathy and VT burden at baseline.
Future Directions and Clinical Applications
The researchers are planning a prospective trial with a larger number of patients to examine safety and efficacy outcomes beyond feasibility. Siontis does not expect proton beam therapy (search) to replace catheter ablation but sees it as an important complementary or salvage option.
"The one distinct characteristic of radioablation and especially proton beam ablation is that it is completely noninvasive," he said. "I do think that radioablation can become an important complementary or a salvage option for patients with a most refractory arrhythmia, or those who are not candidates for any invasive approaches."
While proton beam radioablation offers advantages including lower radiation doses, the technology requires specialized infrastructure only available at selected centers. The research team has learned from this initial series and plans to refine the treatment with gating techniques to correct for motion uncertainties when noninvasively targeting moving cardiac targets.