Stereotactic Arrhythmia Radioablation Research Articles

Response to the Letter by Blank et al. regarding the article: "LINAC-Based STereotactic Arrhythmia Radioablation (STAR) for Paroxysmal Atrial Fibrillation in Elderly: A Prospective Phase II trial."

Response to the Letter by Blank et al. regarding the article: "LINAC-Based STereotactic Arrhythmia Radioablation (STAR) for Paroxysmal Atrial Fibrillation in Elderly: A Prospective Phase II trial."

Left atrial strain after paroxysmal atrial fibrillation linac-based cardiac radioablation in elderly population.

Catheter ablation of atrial fibrillation (AF) may increase the risk of complication in aged patients. Stereotactic arrhythmia radioablation (STAR) is a non-invasive therapeutic alternative for cardiac arrhythmia. This sub-study evaluated left atrial strain (LAS) in elderly AF patients underwent STAR. Symptomatic paroxysmal AF patients aged > 70 years, with antiarrhythmic drugs failure or intolerance, enrolled in a phase II trial that have demonstrated the feasibility of LINAC-based STAR (total dose of 25Gy single fraction delivered in 3min), performed a 15-day electrocardiogram Holter monitoring to detect AF episodes (≥ 30s) and an echocardiographic LAS evaluation before and after STAR (at 1-, 3-, 6- and 12-month). Out 18 patients underwent STAR in the trial, 16 (7 males, 78 ± 5 years) completed the follow-up for LAS study. No baseline difference in echocardiographic and LAS parameters was observed between the 9 patients with AF recurrence during follow-up and those who maintained sinus rhythm. At 6- and 12-month after STAR, LAS reservoir was lower in patients with AF episodes than those without (respectively, p = 0.039 and p = 0.001). Values of left atrial area and volume as well as LAS conduit and contractile phase were not statistically significant different by patient's outcome across evaluations. Although no baseline LAS parameter before STAR seems predict AF recurrence after treatment in elderly patients, lower values of reservoir phase were observed during follow-up in those experiencing AF episodes. More research is needed to better assess the value of LAS monitoring in paroxysmal AF patients underwent Stereotactic cardiac radioablation.

Stereotactic arrhythmia radioablation for refractory ventricular tachycardia. A retrospective analysis and optimisation of the planning phase

Abstract Introduction Stereotactic arrhythmia radioablation (STAR) is used as a rescue treatment for refractory ventricular tachycardia (VT). However, the planning phase to accurately delineate the clinical target volume (CTV) still suffers from limitations due to the incompatibility of data formats between 3D electro-anatomical mapping systems (EAM) used for VT ablation and STAR planning software. The concordance between the CTVs as defined by the planning software (CTVSTAR) and the CTV based on EAM data (CTVEAM) remains unknown. Purpose Within the STOPSTORM European consortium, we compared the concordance between CTVSTAR and CTVEAM in our series of 13 patients (pts) treated by STAR for refractory VT. We also evaluated need for redo ablation of VT after STAR. Method Using the software Slicer3D, two protocols were retrospectively compared: Protocol 1 comprised the manual contouring of the CTVSTAR based on 4D-CT SCAN drawn side-by-side using EAM (Carto3, Biosense Webster) screenshots and diagnostic reports. Protocol 2 comprised semiautomatic segmentation of CTVEAM based on 4D-CT SCAN using imported EAMs annotated with landmarks for VT substrate delimitation. The delineation of CTVEAM included 3 steps: (1) semiautomatic segmentation of ventricular myocardium (VM), the blood-pool of the concerned ventricle and at least 2 additional cardiac cavities; (2) 3D-alignment of EAM with the segmented cavities; and (3), 3D-delineation of CTVSTAR identified as the transmural section of VM segment surrounding the EAM’s VT substrate delimited by STAR tags (Figure 1). Volume overlap (Dice coefficient, 100% meaning complete overlap) and volume absolute difference (VAD, 0% meaning similar volumes) between CTVs were compared. The following cumulative averages were computed over time: redo ablation (RedoA) and CTV. Results Figure 1 illustrates the last treated patient (#13) in whom the delineated volumes, CTVSTAR (red) and CTVEAM (blue), displayed good matching (Dice 72% and VAD 4. Figure 2 shows the comparison between CTVSTAR and CTVEAM for the 13 pts (65±7 yo) treated with STAR, resulting in a mean Dice of 47±17% and mean VAD of 40±51%. Figure 3 shows the cumulative RedoA and the cumulative averaged CTVSTAR and CTVEAM over time. Interestingly, the need for redo ablation decreased with increasing CTVs. Conclusion Our study demonstrates the efficacy of STAR treatment for refractory VT. Our confidence in STAR led to higher CTVs and lower RedoA over time. The high variability of CTV delineation using two different protocols suggests that STAR planning phase can be optimised by appointing intraprocedural anatomical landmarks to the VT substrate.

STereotactic Arrhythmia Radioablation and its place in modern cardiac ElectroPhysiology: Results of an EHRA Survey

Abstract Background Stereotactic arrhythmia radioablation (STAR) is an emerging treatment option for recurrent ventricular tachycardia/fibrillation (VT/VF) in particular in structural heart disease (SHD). However, the current role and envisioned future role of STAR is in clinical practice as viewed by Cardiologists is unknown. Objective To assess the current role of STAR, barriers to its use, and expected future role, within the cardiology community. Methods An online survey was created with the support of the EHRA Scientific Initiatives committee and distributed via newsletters and social media. The survey consisted of 20 multiple-choice questions with a focus on baseline demographics, awareness / access, current use, and the future role of STAR. Results A total of 129 international participants completed the survey, mean age was 43±11 years, 25 (16.4%) were female. Ninety-one (59.9%) participants were cardiac electrophysiologists while 13 (8.6%) were general cardiologists. Nine participants (7%) were unaware of STAR as a therapeutic option. Sixty-four (49.6%) had access to STAR while 62 (48.1%) had treated / referred a patient for treatment. Median number of patients treated was 4 (range 1-100). Common primary indications for STAR were recurrent VT/VF in SDH (45%), recurrent VT/VF without SHD (7.8%) or PVC (3.9%). Based on their knowledge, 49% and 59% of survey participants responded they would consider performing / referring a patient for STAR, respectively. Reported main advantages of STAR were efficacy in the treatment of arrhythmias not amenable to conventional treatment (49%), non-invasive treatment approach with overall low expected acute and short-term procedural risk (23%) and possible higher efficacy than other available treatment options (23%). Survey respondents named one or more previous catheter ablations (CA) or contraindication for CA (79%), diagnosis of SHD (78%), recurrent monomorphic VT with >3 episodes within the preceding 3 months (68%), optimal antiarrhythmic medication (61%) or electrical storm (59%) as prerequisites for the use of STAR. Most respondents foresee a future clinical role for STAR in the treatment of VT/VF with or without underlying SHD (72% and 75%, respectively). Although, only a minority expected a first-line indication for it in with or without SHD (7% and 5%, respectively) and STAR was viewed rather as a bail-out option (48% and 35%, respectively). Conclusions STAR is a new option for the treatment of recurrent VT that appears to gain acceptance within the EP community. Randomized-controlled trials and an EHRA consensus document are critical to further define efficacy, patient populations, as well as the appropriate clinical use for the treatment of VT.Central figureFuture role of STAR

Mid-term outcomes after stereotactic arrhythmia radioablation for refractory ventricular tachycardia

Abstract Introduction stereotactic arrhythmia radioablation (STAR) is used as a rescue treatment for refractory ventricular tachycardia (VT) originating from unreachable myocardial substrate following unsuccessful radiofrequency catheter ablation (RFCA). The mid-term outcomes of STAR, however, remain poorly known. Objective to report the mid-term efficacy and safety outcomes in our series of 21 patients (pts) treated by STAR over 6 years. Methods Inclusion of consecutive pts treated by STAR with a Cyberknife system between 2017 and 2023. 3D-electroanatomical maps (EAM) of the VT substrate during unsuccessful RFCA were used to delineate the planned target volumes (PTV) on a 4D CT scan. Patients were followed up at least every 6 months by echocardiography and ICD interrogation at the outpatient clinic. Results 21 pts [16 (76 %) male, age 66±8 years] with a mean LVEF of 40±15% were included. The underlying substrate was ischemic in 7 (33 %); non-ischemic dilated in 7 (33 %); inflammatory in 4 (19%); hypertrophic in 1 (5%); neoplasic in 1 (5%); and malignant mitral valve prolapse in 1 (5%). A dose of 21±2 Gray was delivered to the PTV (26 ml, IQR 18-43 ml). After a median follow-up of 39 [IQR, 14-48] months, 12 pts (57%) remained in stable condition, 1 (5%) underwent a heart transplantation, 1 (5%) a left ventricular assistance device, 1 (5%) was in an incessant slow VT and 6 (29%) pts died (3 from end stage heart failure). 15 (71%) pts presented VT recurrences [7 (33%) ATPs; 3 (14%) shocks; 4 (19%) VT storm and 1 (5%) with a well-tolerated slow VT (100 bpm) with an LVAD till transplantation, of whom 9 (43%) required redo RFCA. The median value of total ventricular arrhythmic burden (defined as any arrhythmia requiring ICD therapies) decreased significantly from 31 (IQR, 4-100) to 7 (IQR, 1-23) (p<0.05); for nsVT from 57 (IQR, 1.5- 1196) to 41 (IQR, 0.5-584) (p ns); or ICD shocks from 1.5 (IQR, 0-5.5) to 0 (IQR, 0-2) (p<0.05); for ATPs from 21 (IQR, 2.5-94) to 4 (IQR, 0.5-13) (p<0.05). Figure 1 shows a graphic representation of arrhythmic burden before and after STAR. Conclusion in this cohort of highly selected pts with refractory VT, STAR significantly reduced the arrhythmic burden by a factor of 4 over a 3-year follow-up. Death rate remained high (29%), mostly by terminal heart failure. Nevertheless, a high proportion of pts had VT recurrences that were successfully managed by redo RFCA.VT burden before and after STAR

LINAC-Based STereotactic Arrhythmia Radioablation (STAR) for paroxysmal atrial fibrillation in elderly: a prospective phase II trial

Abstract Background and aims Stereotactic arrhythmia radioablation (STAR) is a novel therapeutic approach for cardiac arrhythmias. The aim of this trial is to investigate the feasibility of STAR for the treatment of paroxysmal atrial fibrillation (AF) in elderly patients. Method inclusion criteria were: age > 70 years, symptomatic AF, antiarrhythmic drugs failure or intolerance. All patients underwent to 4D cardiac Computed Tomography simulation. The clinical target volume was identified in the area around pulmonary veins (PV). STAR was performed with a total dose of 25 Gy (single fraction) delivered in 3 minutes. Results Twenty patients were enrolled and 18 underwent STAR. One patient withdrew informed consent before treatment and 1 patient was excluded due to unfavorable esophagus position. With a median follow-up (FU) of 16 months (range 12-23), no acute toxicity more than grade 3 was reported. Five patients had a grade 1 esophagitis 24 hours after STAR; eight patients had an asymptomatic grade 1 pericardial effusion, one patient had a torsade de pointes treated effectively by electrical cardioversion and subsequent cardiac ICD implantation. Most patients had a significant reduction in AF episodes. Five patients, due to arrhythmias recurrences after STAR, performed electrophysiological study documenting successful PV isolation. Finally, a significant improvement of quality of life was documented (48 ± 15 at enrollment vs 75 ± 15 at 12 months FU; p < 0.001). Conclusion The present phase II trial demonstrated the feasibility of STAR in paroxysmal AF elderly patients and its potential role in increasing the quality of life. Surely, more robust data are needed about safety and efficacy.

A VENTRICULAR TACHYCARDIA CASE NOT TREATABLE WITH TRANSCATHETER ABLATION DUE TO APICAL THROMBOSIS OF THE LEFT VENTRICLE RESOLVED WITH RADIOTHERAPY BASED ON THE NON–INVASIVE MAPPING SYSTE

Abstract The clinical case focuses on a 52–year–old man smoker, heavy alcohol consumer. In 2017 he began with sustained ventricular tachycardia (VT) effectively treated with DC–shock. The following ECG showed signs of anterior necrosis. Severe left ventricular (LV) dilatation, apical thrombosis and severe impairment of LV function were found on echocardiogram. Angiography was performed and LAD occlusion was found. Since of 68% necrosis of the LV at myocardial scintigraphy, no revascularization was performed. He underwent to a dual chamber ICD implantation and started oral anticoagulation therapy. In the following years recurrence of arrhythmic episodes, despite the optimization of antiarrhythmic therapy, led the patient to numerous hospitalizations. Unfortunately the persistence of the apical thrombosis, made transcatheter ablation NOT possible. The only chance for the patient remained stereotactic arrhythmia radioablation. But which area of the LV to highlight as responsible for the arrhythmia and how to program the radiotherapy treatment plan was a challenging problem. We proposed in March 2023 non–invasive mapping of arrhythmia using Cardioinsight. The patient performed heart high–resolution computed tomography (CT) for the anatomical reconstruction with precise spatial resolution of all LV aereas and surrounding structures. A 252–electrode vest is applied to the patient’s torso and connected to the system Cardioinsight. A programmed ventricular stimulation was performed using ICD inducing two VT morphologies. Through electroanatomical mapping we identified the mid LV antero–septal and infero–septal sites as target areas. Thanks to multidisciplinary team a personalized treatment plan was created to deliver an effective lesion in the target area and minimize exposure to nearby organs at risk. The treatment was generated, optimized and delivered by TrueBeam, lasted 3 minutes and no complications arose. The patient was quickly discharged in good clinical condition. After 3 months of clinical well–being he was hospitalized for a single episode of VT. Up to now no hospitalizations occurred. This treatment may represent a "bail–out" choice in patients with advanced heart failure with arrhythmic storm who have exhausted all other therapeutic options.

Stereotactic arrhythmia radioablation and its implications for modern cardiac electrophysiology: results of an EHRA survey.

Stereotactic arrhythmia radioablation (STAR) is a treatment option for recurrent ventricular tachycardia/fibrillation (VT/VF) in patients with structural heart disease (SHD). The current and future role of STAR as viewed by cardiologists is unknown. The study aimed to assess the current role, barriers to application, and expected future role of STAR. An online survey consisting of 20 questions on baseline demographics, awareness/access, current use, and the future role of STAR was conducted. A total of 129 international participants completed the survey [mean age 43 ± 11 years, 25 (16.4%) female]. Ninety-one (59.9%) participants were electrophysiologists. Nine participants (7%) were unaware of STAR as a therapeutic option. Sixty-four (49.6%) had access to STAR, while 62 (48.1%) had treated/referred a patient for treatment. Common primary indications for STAR were recurrent VT/VF in SHD (45%), recurrent VT/VF without SHD (7.8%), or premature ventricular contraction (3.9%). Reported main advantages of STAR were efficacy in the treatment of arrhythmias not amenable to conventional treatment (49%) and non-invasive treatment approach with overall low expected acute and short-term procedural risk (23%). Most respondents have foreseen a future clinical role of STAR in the treatment of VT/VF with or without underlying SHD (72% and 75%, respectively), although only a minority expected a first-line indication for it (7% and 5%, respectively). Stereotactic arrhythmia radioablation as a novel treatment option of recurrent VT appears to gain acceptance within the cardiology community. Further trials are critical to further define efficacy, patient populations, as well as the appropriate clinical use for the treatment of VT.

Impact of abdominal compression on heart and stomach motion for stereotactic arrhythmia radioablation.

To evaluate the effectiveness of abdominal compression (AC) as a respiratory motion management method for the heart and stomach during stereotactic arrhythmia radioablation (STAR). 4D computed tomography (4DCT) scans of patients imaged with AC or without AC (free-breathing: FB) were obtained from ventricular-tachycardia (VT) (n=3), lung cancer (n=18), and liver cancer (n=18) patients. Patients treated for VT were imaged both FB and with AC. Lung and liver patients were imaged once with FB or with AC, respectively. The heart, left ventricle (LV), LV components (LVCs), and stomach were contoured on each phase of the 4DCTs. Centre of mass (COM) translations in the left/right (LR), ant/post (AP), and sup/inf (SI) directions were measured for each structure. Minimum distances between LVCs and the stomach over the respiratory cycle were also measured on each 4DCT phase. Mann-Whitney U-tests were performed between AC and FB datasets with a significance of α=0.05. No statistical difference (all p values were>0.05) was found in COM translations between FB and AC patient datasets for all contoured cardiac structures. A reduction in COM translation with AC relative to FB was patient, direction, and structure specific for the three VT patients. A significant decrease in the AP range of motion of the stomach was observed under AC compared to FB. No statistical difference was found between minimum distances to the stomach and LVCs between FB and AC. AC was not a consistent motion management method for STAR, nor does not uniformly affect the separation distance between LVCs and the stomach. If AC is employed in future STAR protocols, the motion of the target volume and its relative distance to the stomach should be compared on two 4DCTs: one while the patient is FB and one under AC.

Patient vulnerability in stereotactic arrhythmia radioablation(STAR): apreliminary ethical appraisal from the STOPSTORM.eu consortium.

This preliminary ethical appraisal from the STOPSTORM.eu consortium is meant to raise critical points that clinicians administering stereotactic arrhythmia radioablation should consider to meet the highest standards in medical ethics and thus promote quality of life of patients recruited for radiotherapy treatments at astage in which they experience asignificant degree of vulnerability.

Ventricular Tachycardia Catheter Ablation: Retrospective Analysis and Prospective Outlooks-A Comprehensive Review.

Ventricular tachycardia is a potentially life-threatening arrhythmia associated with an overall high morbi-mortality, particularly in patients with structural heart disease. Despite their pivotal role in preventing sudden cardiac death, implantable cardioverter-defibrillators, although a guideline-based class I recommendation, are unable to prevent arrhythmic episodes and significantly alter the quality of life by delivering recurrent therapies. From open-heart surgical ablation to the currently widely used percutaneous approach, catheter ablation is a safe and effective procedure able to target the responsible re-entry myocardial circuit from both the endocardium and the epicardium. There are four main mapping strategies, activation, entrainment, pace, and substrate mapping, each of them with their own advantages and limitations. The contemporary guideline-based recommendations for VT ablation primarily apply to patients experiencing antiarrhythmic drug ineffectiveness or those intolerant to the pharmacological treatment. Although highly effective in most cases of scar-related VTs, the traditional approach may sometimes be insufficient, especially in patients with nonischemic cardiomyopathies, where circuits may be unmappable using the classic techniques. Alternative methods have been proposed, such as stereotactic arrhythmia radioablation or radiotherapy ablation, surgical ablation, needle ablation, transarterial coronary ethanol ablation, and retrograde coronary venous ethanol ablation, with promising results. Further studies are needed in order to prove the overall efficacy of these methods in comparison to standard radiofrequency delivery. Nevertheless, as the field of cardiac electrophysiology continues to evolve, it is important to acknowledge the role of artificial intelligence in both the pre-procedural planning and the intervention itself.

Cardiac Arrhythmias in Patients Treated for Lung Cancer: A Review.

Cardio-oncology currently faces one of the greatest challenges in the field of health care. The main goal of this discipline is to ensure that patients treated for cancer do not suffer or die from cardiovascular disease. The number of studies on the mechanisms of heart injury during cancer treatment is constantly increasing. However, there is insufficient data on heart rhythm disorders that may result from this treatment. This issue seems to be particularly important in patients with lung cancer, in whom anticancer therapy, especially radiotherapy, may contribute to the onset of cardiac arrhythmias. The observed relationship between cardiac dosimetry and radiotherapy-induced cardiotoxicity in lung cancer treatment may explain the increased mortality from cardiovascular causes in patients after chest irradiation. Further research is essential to elucidate the role of cardiac arrhythmias in this context. Conversely, recent reports have highlighted the application of stereotactic arrhythmia radioablation (STAR) in the treatment of ventricular tachycardia. This review of available studies on the epidemiology, pathogenesis, diagnosis, and treatment of arrhythmias in patients treated for lung cancer aims to draw attention to the need for regular cardiological monitoring in this group of patients. Improving cardiac care for patients with lung cancer has the potential to enhance their overall therapeutic outcomes.

The state‐of‐the‐art technic of stereotactic radioablation for the treatment of cardiac arrhythmias: An overview

AbstractIntroductionCardiac arrhythmias, including ventricular tachycardia (VT), stand as a significant threat to health, often leading to mortality and sudden cardiac death. While conventional treatments for VT exhibit efficacy, cases of refractory VT pose challenges. Stereotactic Arrhythmia Radioablation (STAR) offers a novel approach, delivering precise high‐dose radiation to well‐defined targets with minimal collateral damage. This study explores the potential of STAR as an alternative therapy, especially for high‐risk patients or those with refractory VT.MethodsThis research reviews ongoing studies and preliminary investigations into the evaluation of the efficacy and safety of STAR. The method involves targeted radiation delivery, assessing reductions in VT recurrence and the early safety profile in refractory VT patients. However, given STAR's early stage and limited clinical evidence, cautious interpretation is advised.ResultsPreliminary findings indicate a reduction in VT recurrence with STAR, suggesting promise as a therapeutic option. Early safety profiles are encouraging, but definitive statements on efficacy and safety require further investigation. Positive initial outcomes underscore the need for additional data and long‐term studies.ConclusionStereotactic Arrhythmia Radioablation is recently emerging as a promising treatment for refractory VT. While early results are encouraging, careful interpretation is needed, due to STAR's early stages. Ongoing investigations are critical for a comprehensive understanding of its long‐term efficacy and tolerability. This review provides fundamental insights into STAR's background, principles, pre‐treatment procedures, clinical implications, and toxicity, setting the stage for future research in this evolving therapeutic field.

Integration of electro-anatomical maps in the planning phase of stereotactic arrhythmia radioablation for refractory ventricular tachycardia

Abstract Introduction Despite the efficacy of stereotactic arrhythmia radioablation (STAR) for the treatment of refractory ventricular tachycardia (VT), the planning phase to precisely delineate the arrhythmogenic substrate still suffers from limitations due to the incompatibility of data formats between 3D electro-anatomical mapping systems (EAM) and STAR planning software (CyberKnife). Purpose Within the STOPSTORM European consortium, we present a workflow to integrate all 3D EAM data (e.g. voltage, activation time, anatomical tags) into the STAR planning software using the open source software Slicer3D to improve targeting of the arrhythmogenic substrate. Method Two protocols were compared retrospectively. Protocol 1 (STAR gold-standard) comprised the manual contouring of the clinical target volume (CTV) on planning 4D-CAT SCAN drawn side-by-side using EAM (Carto3, Biosense Webster) screen-shots and diagnostic reports. Protocol 2 comprised semiautomatic segmentation of CTV on planning 4D-CAT SCAN using imported EAMs annotated with landmarks for VT target delimitation. The semiautomatic segmentation of CTVs included three steps: (1) semiautomatic segmentation of ventricular myocardium (VM), the blood-pool of the concerned ventricle and at least two additional cardiac cavities; (2) 3D alignment of EAM with the segmented cavities; and (3), 3D delineation of CTV identified as the transmural section of VM segment surrounding the EAM’s VT target delimited by the annotated landmarks. The volume overlap (Dice coefficient) and the absolute difference of the CTVs obtained with the two protocols were compared. Both measurements were expressed in percentage as follows: Dice coefficient 0% means no overlap and 100% complete overlap; absolute difference of volumes 0% means no difference and 100% means that one CTV was twice the size of the CTV generated by the other protocol. Results Both protocols were applied to four patients (65.5 ± 8.5 yo) with refractory VT successfully treated with STAR. Figure 1 shows an example (Patient 1) of the CTV contouring using the CARTO EAMs aligned with the CT images in Slicer3D. Figure 2 illustrates significant mismatch between the segmented CTVs of the two protocols. The median volume overlap of the CTVs was 44%, while the median volume absolute difference was 35%. Table 1 reports detailed results. Conclusion Our study reveals a high variability of CTV delineation for STAR using two different protocols. The intraprocedural assignment of anatomical landmarks for VT target delimitation on EAM appears promising to improve CTV delineation. Further research is needed to evaluate the correlation between STAR outcome and CTV delineation accuracy.

Institutional experience report on the target contouring workflow in the radiotherapy department for stereotactic arrhythmia radioablation delivered on conventional linear accelerators.

In stereotactic arrhythmia radioablation (STAR), the target is defined using multiple imaging studies and amultidisciplinary team consisting of electrophysiologist, cardiologist, cardiac radiologist, and radiation oncologist collaborate to identify the target and delineate it on the imaging studies of interest. This report describes the workflow employed in our radiotherapy department to transfer the target identified based on electrophysiology and cardiology imaging to the treatment planning image set. The radiotherapy team was presented with an initial target in cardiac axes orientation, contoured on awideband late gadolinium-enhanced (WB-LGE) cardiac magnetic resonance (CMR) study, which was subsequently transferred to the computed tomography (CT) scan used for treatment planning-i.e., the average intensity projection (AIP) image set derived from a4DCT-via an axial CMR image set, using rigid image registration focused on the target area. The cardiac and the respiratory motion of the target were resolved using ciné-CMR and 4D CT imaging studies, respectively. The workflow was carried out for 6patients and resulted in an internal target defined in standard anatomical orientation that encompassed the cardiac and the respiratory motion of the initial target. An image registration-based workflow was implemented to render the STAR target on the planning image set in aconsistent manner, using commercial software traditionally available for radiation therapy.

A target definition based on electroanatomic maps for stereotactic arrhythmia radioablation

PurposeIdentifying the target region is critical for successfully treating ventricular tachycardia (VT) with single fraction stereotactic arrhythmia radioablation (STAR). We report the feasibility of target definition based on direct co-registration of electroanatomic maps (EAM) and radioablation planning images. Materials and methodsThe EAM consists of 3D cardiac anatomy representation with electrical activity at endocardium and is acquired by a cardiac electrophysiologist (CEP) during electrophysiology study. The CEP generates an EAM using a 3D cardiac mapping system anticipating radioablation planning. Our in-house software read these non-DICOM EAMs, registered them to a planning image set, and converted them to DICOM structure files. The EAM based target volume was finalized based on a consensus of CEPs, radiation oncologists and medical physicists, then expanded to ITV and PTV. The simulation, planning, and treatment is performed with a standard STAR technique: a single fraction of 25 Gy using volumetric-modulated arc therapy or dynamic conformal arc therapy depending on the target shape. ResultsSeven patients with refractory VT were treated by defining the target based on registering EAMs on the planning images. Dice similarity indices between reference map and reference contours after registration were 0.814 ± 0.053 and 0.575 ± 0.199 for LV and LA/RV, respectively. ConclusionsThe quality of the transferred EAMs on the MR/CT images was sufficient to localize the treatment region. Five of 7 patients demonstrated a dramatic reduction in VT events after 6 weeks. Longer follow-up is required to determine the true safety and efficacy of this therapy using EAM-based direct registration method.

Description of multiparametric targeting techniques for stereotactic arrhythmia radioablation in refractory ventricular tachycardia: A quaternary medical center experience

Background: Ventricular tachycardia (VT) is a potentially life-threatening arrhythmia which remains a major contributor to cardiac morbidity and mortality worldwide. Recently the use of stereotactic radiation has demonstrated efficacy, although standardization of methodology is lacking and variations in technique exist. In this paper, we discuss our outcomes as well as the various options available and the proposed indications for each.Methods: 12-lead EKGs and device-obtained tracings were used to approximately localize the arrhythmogenic origin and to define the arrhythmic mechanism. When feasible, electrophysiology studies (EPS) with 3-D electroanatomic (EA) mapping during which a 3-D electroanatomic substrate map was created to delineate cardiac structures, identify areas of low voltage scar and confirm arrhythmic circuits. A 4-D cardiac magnetic resonance imaging (cMRI) or cardiac computed tomography (cCT) was performed to delineate cardiac geometry and structures. The Stereotactic arrhythmia radioablation (STAR) treatment plans delivered a total dose of 25 Gy in a single treatment fraction covering the entire arrhythmogenic target.Results: Six of the nine patients showed a reduction in VT events at 6 weeks post STAR. One patient underwent cardiac transplantation two weeks following STAR. Excluding this patient from the analysis, all but one patient had a dramatic diminution in VT events (to 0) at 6 months post-procedure, including both patients with an LVAD. Six of the nine patients survived at least 4 months post procedure event free and 6 patients survive to date. The lone patient who did not respond died 13 months post procedure, however he had no further defibrillator discharges. Another patient died two months post procedure from uncontrolled multiple myeloma. One patient developed an asymptomatic pleural effusion, but no serious STAR-induced postoperative complications occurred.Conclusions: STAR appears to be an effective therapy for refractory ventricular tachycardia, although long term data are still developing. Additional clinical trials and techniques are in development and STAR programs should be encouraged for additional well-equipped centers with experienced multidisciplinary clinicians.

Refining critical structure contouring in STereotactic Arrhythmia Radioablation (STAR): Benchmark results and consensus guidelines from the STOPSTORM.eu consortium

Background and purposeIn patients with recurrent ventricular tachycardia (VT), STereotactic Arrhythmia Radioablation (STAR) shows promising results. The STOPSTORM.eu consortium was established to investigate and harmonise STAR treatment in Europe. The primary goals of this benchmark study were to standardise contouring of organs at risk (OAR) for STAR, including detailed substructures of the heart, and accredit each participating centre. Materials and MethodsCentres within the STOPSTORM.eu consortium were asked to delineate 31 OAR in three STAR cases. Delineation was reviewed by the consortium expert panel and after a dedicated workshop feedback and accreditation was provided to all participants. Further quantitative analysis was performed by calculating DICE similarity coefficients (DSC), median distance to agreement (MDA), and 95th percentile distance to agreement (HD95). ResultsTwenty centres participated in this study. Based on DSC, MDA and HD95, the delineations of well-known OAR in radiotherapy were similar, such as lungs (median DSC = 0.96, median MDA = 0.1 mm and median HD95 = 1.1 mm) and aorta (median DSC = 0.90, median MDA = 0.1 mm and median HD95 = 1.5 mm). Some centres did not include the gastro-oesophageal junction, leading to differences in stomach and oesophagus delineations. For cardiac substructures, such as chambers (median DSC = 0.83, median MDA = 0.2 mm and median HD95 = 0.5 mm), valves (median DSC = 0.16, median MDA = 4.6 mm and median HD95 = 16.0 mm), coronary arteries (median DSC = 0.4, median MDA = 0.7 mm and median HD95 = 8.3 mm) and the sinoatrial and atrioventricular nodes (median DSC = 0.29, median MDA = 4.4 mm and median HD95 = 11.4 mm), deviations between centres occurred more frequently. After the dedicated workshop all centres were accredited and contouring consensus guidelines for STAR were established. ConclusionThis STOPSTORM multi-centre critical structure contouring benchmark study showed high agreement for standard radiotherapy OAR. However, for cardiac substructures larger disagreement in contouring occurred, which may have significant impact on STAR treatment planning and dosimetry evaluation. To standardize OAR contouring, consensus guidelines for critical structure contouring in STAR were established.

One Year Follow-up and Toxicity Review in a Series of 6 Patients Receiving Stereotactic Arrhythmia Radioablation for Ventricular Tachycardia

Stereotactic body radiation therapy (SBRT) to arrhythmogenic scar regions defined by noninvasive cardiac mapping has recently been described for patients with treatment refractory ventricular tachycardia (VT). Long-term outcomes and both intra- and extra-cardiac toxicities are not well described in this patient population. We report the outcomes following at least 1-year post-treatment along with toxicity for 6 patients treated with this technique in our institution. A total of 6 patients treated between 2019 and 2022 with refractory VT with previously failed ablations and at least one anti-arrhythmic drug was treated at our institution. All were treated with 25 Gy in a single fraction to the suspected arrhythmogenic scar. Cardiac microstructure contouring was done following the atlas by Duane et al. 2017. Implantable cardioverter defibrillator (ICD) interrogation was performed regularly by the treating cardiologist to assess the number of VT and ICD events, and, patients were seen immediately following SBRT, and at 3, 6, and 12 months respectively. Computed tomography of the chest was done at 3 months to assess for radiation induced pneumonitis and transthoracic echocardiograms were done as per the cardiologist's discretion. Radiation toxicity was evaluated using CTCAE v5.0. The median follow-up time for the 6 evaluated patients is 24 months. Three patients (50%) remained VT free during the one-year period post SBRT. Two of these patients remain VT free and are either on reduced or discontinued anti-arrhythmic drugs, while another failed at 24 months in an area of the arrhythmogenic substrate that was intentionally not irradiated due to organ at risk safety concerns. Among those that failed, the median time to failure was 4 months (range 3-5 months). All 6 patients tolerated treatment with no immediate acute side effects. Three (50%) of patients had no acute clinical or radiographic side effects. Grade 1 esophagitis, grade 1 fatigue, and grade 1 cough was reported in 1 (17%) patient each (all different patients), and 1 patient required hospitalization 4 months after SBRT for a heart failure exacerbation (potentially SBRT related). One patient (17%) died within 3 months following treatment but their death was not attributed to radiation treatment. No cardiac microstructure toxicity has been reported to date. Despite increasing reports in the literature, there are no established criteria to predict success for SBRT in the context of treatment-refractory VT, or the optimal treatment dose for success, making it difficult to identify optimal patients. Current limited evidence suggests that this technique may be a relatively safe approach to provide an acute reduction in VT burden for those refractory to standard of care and has an acceptable acute toxicity profile however longer term follow-up is required. Long term toxicity, specifically to cardiac microstructures, and dose optimization is currently are the focus of ongoing study.

Interobserver variability in target definition for stereotactic arrhythmia radioablation.

Stereotactic arrhythmia radioablation (STAR) is a potential new therapy for patients with refractory ventricular tachycardia (VT). The arrhythmogenic substrate (target) is synthesized from clinical and electro-anatomical information. This study was designed to evaluate the baseline interobserver variability in target delineation for STAR. Delineation software designed for research purposes was used. The study was split into three phases. Firstly, electrophysiologists delineated a well-defined structure in three patients (spinal canal). Secondly, observers delineated the VT-target in three patients based on case descriptions. To evaluate baseline performance, a basic workflow approach was used, no advanced techniques were allowed. Thirdly, observers delineated three predefined segments from the 17-segment model. Interobserver variability was evaluated by assessing volumes, variation in distance to the median volume expressed by the root-mean-square of the standard deviation (RMS-SD) over the target volume, and the Dice-coefficient. Ten electrophysiologists completed the study. For the first phase interobserver variability was low as indicated by low variation in distance to the median volume (RMS-SD range: 0.02-0.02 cm) and high Dice-coefficients (mean: 0.97 ± 0.01). In the second phase distance to the median volume was large (RMS-SD range: 0.52-1.02 cm) and the Dice-coefficients low (mean: 0.40 ± 0.15). In the third phase, similar results were observed (RMS-SD range: 0.51-1.55 cm, Dice-coefficient mean: 0.31 ± 0.21). Interobserver variability is high for manual delineation of the VT-target and ventricular segments. This evaluation of the baseline observer variation shows that there is a need for methods and tools to improve variability and allows for future comparison of interventions aiming to reduce observer variation, for STAR but possibly also for catheter ablation.