Primary bone diffuse large B-cell lymphoma (PB-DLBCL): a distinct extranodal lymphoma of germinal centre origin, with a common EZB-like mutational profile and good prognosis.

AIMS: Primary bone diffuse large B-cell lymphoma (PB-DLBCL) is not recognized as a separate entity by the current classification systems. Here we define and highlight its distinctive clinical presentation, morphology, phenotype, gene expression profile (GEP), and molecular genetics. METHODS: We collected 27 respective cases and investigated their phenotype, performed gDNA panel sequencing covering 172 genes, and carried out fluorescence in situ hybridization to evaluate MYC, BCL2, and BCL6 translocations. We attempted to genetically subclassify cases using the Two-step classifier and performed GEP for cell-of-origin subtyping and in silico comparison to uncover up- and downregulated genes as opposed to other DLBCL. RESULTS: Most cases (n = 22) were germinal centre B-cell-like (GCB) by immunohistochemistry and all by GEP. Additionally, PB-DLBCL had a mutational profile similar to follicular lymphoma and nodal GCB-DLBCL, with the exception of more frequent TP53 and B2M mutations. The GEP of PB-DLBCL was unique, and the frequency of BCL2 rearrangements was lower compared to nodal GCB-DLBCL. The Two-step classifier categorized eight of the cases as EZB, three as ST2, and one as MCD. CONCLUSION: This study comprehensively characterizes PB-DLBCL as a separate entity with distinct clinical and morpho-molecular features. These insights may aid in developing tailored therapeutic strategies and shed light on its pathogenesis.

Whole brain radiation therapy for patients with brain metastases: survival outcomes and prognostic factors in a contemporary institutional series.

PURPOSE: To study survival outcomes and prognostic factors in patients undergoing whole brain radiation therapy (WBRT) for brain metastases in the contemporary setting. METHODS: Patients undergoing WBRT from 2013-2021 were retrospectively included in an ethics-approved institutional database. Patient and treatment characteristics were assessed, including patient age, primary tumor histology, Karnofsky Performance Status (KPS), extracranial disease, as well as WBRT dose. Overall survival (OS) was calculated from onset of WBRT using the Kaplan-Meier method. RESULTS: A total of 328 patients (median age 63 years) were included. Most patients (52%) had ≥ 10 brain metastases, and 17% had leptomeningeal disease. WBRT was delivered with 10â€¯× 3 Gy (64%), 5â€¯× 4 Gy (25%), or other regimens (11%). Median follow-up was 4.4 months (range, 0.1-154.3), and median OS was 4.7 months (95%CI, 3.8-6.0). OS differed between histologies (p = 0.01), with the longest survival seen in breast cancer (median 7.7 months). Patients with KPS of 90-100 survived for a median of 8.3 months, compared to 4.1 months with KPS 70-80, and 1.7 months with KPS < 70 (p < 0.01). Multivariate analyses revealed that KPS had the largest impact on survival. Patients who received a WBRT dose of ≥ 30 Gy also had a reduced risk of death (HR 0.45; p < 0.001). Survival differed between subgroups reclassified according to the Rades scoring system (p < 0.01). CONCLUSION: Survival outcomes of patients undergoing WBRT in the contemporary era appear comparable to historical cohorts, although individual patient factors need to be considered. Patients with otherwise favorable prognostic factors may benefit from longer-course WBRT.

Follow-up strategies after trimodal treatment for muscle-invasive bladder cancer: a systematic review.

PURPOSE: Optimal follow-up strategies following trimodal treatment for muscle invasive bladder cancer play a crucial role in detecting and managing relapse and side-effects. This article provides a comprehensive summary of the patterns and risk factors of relapse, functional outcomes, and follow-up protocols. METHODS: A systematic literature search on PubMed and review of current guidelines and institutional follow-up protocols after trimodal therapy were conducted. RESULTS: Out of 200 identified publications, 43 studies (28 retrospective, 15 prospective) were selected, encompassing 7447 patients (study sizes from 24 to 728 patients). Recurrence rates in the urinary bladder varied between 14-52%; 3-16% were muscle-invasive while 11-36% were non-muscle invasive. Nodal recurrence occurred at 13-16% and distant metastases at 15-35%. After 5 and 10 years of follow-up, around 60-85% and 45-75% of patients could preserve their bladder, respectively. Various prognostic risk factors associated with relapse and inferior survival were proposed, including higher disease stage (> c/pT2), presence of extensive/multifocal carcinoma in situ (CIS), hydronephrosis, multifocality, histological subtypes, incomplete transurethral resection of bladder tumor (TURBT) and incomplete response to radio-chemotherapy. The analyzed follow-up guidelines varied slightly in terms of the number, timing, and types of investigations, but overall, the recommendations were similar. CONCLUSION: Randomized prospective studies should focus on evaluating the impact of specific follow-up protocols on oncological and functional outcomes following trimodal treatment for muscle-invasive bladder cancer. It is crucial to evaluate personalized adaption of follow-up protocols based on established risk factors, as there is potential for improved patient outcomes and resource allocation.

Single-dose carboplatin followed by involved-node radiotherapy for stage IIA and stage IIB seminoma (SAKK 01/10): a single-arm, multicentre, phase 2 trial.

BACKGROUND: Standard treatment options for patients with stage IIA or stage IIB seminoma include either para-aortic and pelvic radiotherapy or three to four cycles of cisplatin-based combination chemotherapy. These options result in 3-year progression free survival rates of at least 90%, but bear risks for acute and late toxic effects, including secondary malignancies. We tested a novel approach combining de-escalated chemotherapy with de-escalated involved node radiotherapy, with the aim of reducing toxicity while preserving efficacy. METHODS: In the single-arm, multicentre, phase 2 SAKK 01/10 trial, patients with stage IIA or IIB classic seminoma (either at primary diagnosis or at relapse during active surveillance for stage I) were enrolled at ten centres of the Swiss Group for Clinical Cancer Research and ten centres of the German Testicular Cancer Study Group. WHO performance status 0-2, age 18 years or older, and adequate bone marrow and kidney function were required for eligibility. Treatment comprised one cycle of carboplatin (area under the curve 7) followed by involved-node radiotherapy (30 Gy in 15 fractions for stage IIA disease and 36 Gy in 18 fractions for stage IIB disease). The primary endpoint was 3-year progression-free survival. Efficacy analyses were done on the full analysis set, which comprised all patients who signed the informed consent, were registered in the trial, initiated trial treatment, and met all medically relevant inclusion or exclusion criteria. Safety was assessed in all patients who were treated at least once with one of the trial treatments. The study is ongoing but no longer recruiting, and is registered with Clinicaltrials.gov, NCT01593241. FINDINGS: Between Oct 18, 2012, and June 22, 2018, 120 patients were registered in the study. 116 patients were eligible and started treatment according to the study protocol (46 patients with stage IIA disease and 70 with stage IIB disease). After a median follow-up of 4·5 years (IQR 3·9-6·0), 3-year progression-free survival was 93·7% (90% CI 88·5-96·6). With a target progression-free survival of 95% at 3 years, the primary endpoint was not met. Acute treatment-related adverse events of any grade were noted in 58 (48%) of 116 patients, and grade 3 or 4 treatment-related adverse events occurred in the form of neutropenia in five (4%) patients, thrombocytopenia in three (3%) patients, and vomiting in one (1%) patient. No treatment-related deaths and no late treatment-related adverse events were reported. Serious adverse events were reported in five (4%) of 116 patients (one transient creatinine increase and four second primary tumours). INTERPRETATION: Despite the fact that the primary endpoint was not met, we observed favourable 3-year progression-free survival with single-dose carboplatin area under the curve 7 and involved-node radiotherapy, with minimal toxic effects. Our findings might warrant discussion with patients about the SAKK 01/10 regimen as an alternative to standard-of-care treatment, but more research on this strategy is needed. FUNDING: Swiss State Secretariat for Education, Research and Innovation and Rising Tide Foundation for Clinical Cancer Research.

Postoperative radiotherapy for meningiomas - a decision-making analysis.

BACKGROUND: The management of meningiomas is challenging, and the role of postoperative radiotherapy is not standardized. METHODS: Radiation oncology experts in Swiss centres were asked to participate in this decision-making analysis on the use of postoperative radiotherapy (RT) for meningiomas. Experts from ten Swiss centres agreed to participate and provided their treatment algorithms. Their input was converted into decision trees based on the objective consensus methodology. The decision trees were used as a basis to identify consensus and discrepancies in clinical routine. RESULTS: Several criteria used for decision-making in postoperative RT in meningiomas were identified: histological grading, resection status, recurrence, location of the tumour, zugzwang (therapeutic need to treat and/or severity of symptoms), size, and cell division rate. Postoperative RT is recommended by all experts for WHO grade III tumours as well as for incompletely resected WHO grade II tumours. While most centres do not recommend adjuvant irradiation for WHO grade I meningiomas, some offer this treatment in recurrent situations or routinely for symptomatic tumours in critical locations. The recommendations for postoperative RT for recurrent or incompletely resected WHO grade I and II meningiomas were surprisingly heterogeneous. CONCLUSIONS: Due to limited evidence on the utility of postoperative RT for meningiomas, treatment strategies vary considerably among clinical experts depending on the clinical setting, even in a small country like Switzerland. Clear majorities were identified for postoperative RT in WHO grade III meningiomas and against RT for hemispheric grade I meningiomas outside critical locations. The limited data and variations in clinical recommendations are in contrast with the high prevalence of meningiomas, especially in elderly individuals.

Therapy of clinical stage IIA and IIB seminoma: a systematic review.

PURPOSE: The optimal treatment for clinical stage (CS) IIA/IIB seminomas is still controversial. We evaluated current treatment options. METHODS: A systematic review was performed. Only randomized clinical trials and comparative studies published from January 2010 until February 2021 were included. Search items included: seminoma, CS IIA, CS IIB and therapy. Outcome parameters were relapse rate (RR), relapse-free (RFS), overall and cancer-specific survival (OS, CSS). Additionally, acute and long-term side effects including secondary malignancies (SMs) were analyzed. RESULTS: Seven comparative studies (one prospective and six retrospective) were identified with a total of 5049 patients (CS IIA: 2840, CS IIB: 2209). The applied treatment modalities were radiotherapy (RT) (n = 3049; CS IIA: 1888, CSIIB: 1006, unknown: 155) and chemotherapy (CT) or no RT (n = 2000; CS IIA: 797, CS IIB: 1074, unknown: 129). In CS IIA, RRs ranged from 0% to 4.8% for RT and 0% for CT. Concerning CS IIB RRs of 9.5%-21.1% for RT and of 0%-14.2% for CT have been reported. 5-year OS ranged from 90 to 100%. Only two studies reported on treatment-related toxicities. CONCLUSIONS: RT and CT are the most commonly applied treatments in CS IIA/B seminoma. In CS IIA seminomas, RRs after RT and CT are similar. However, in CS IIB, CT seems to be more effective. Survival rates of CS IIA/B seminomas are excellent. Consequently, long-term toxicities and SMs are important survivorship issues. Alternative treatment approaches, e.g., retroperitoneal lymph node dissection (RPLND) or dose-reduced sequential CT/RT are currently under prospective investigation.

Measures of infection prevention and incidence of SARS-CoV-2 infections in cancer patients undergoing radiotherapy in Germany, Austria and Switzerland.

PURPOSE: COVID-19 infection has manifested as a major threat to both patients and healthcare providers around the world. Radiation oncology institutions (ROI) deliver a major component of cancer treatment, with protocols that might span over several weeks, with the result of increasing susceptibility to COVID-19 infection and presenting with a more severe clinical course when compared with the general population. The aim of this manuscript is to investigate the impact of ROI protocols and performance on daily practice in the high-risk cancer patients during this pandemic. METHODS: We addressed the incidence of positive COVID-19 cases in both patients and health care workers (HCW), in addition to the protective measures adopted in ROIs in Germany, Austria and Switzerland using a specific questionnaire. RESULTS: The results of the questionnaire showed that a noteworthy number of ROIs were able to complete treatment in SARS-CoV­2 positive cancer patients, with only a short interruption. The ROIs reported a significant decrease in patient volume that was not impacted by the circumambient disease incidence, the type of ROI or the occurrence of positive cases. Of the ROIs 16.5% also reported infected HCWs. About half of the ROIs (50.5%) adopted a screening program for patients whereas only 23.3% also screened their HCWs. The range of protective measures included the creation of working groups, instituting home office work and protection with face masks. Regarding the therapeutic options offered, curative procedures were performed with either unchanged or moderately decreased schedules, whereas palliative or benign radiotherapy procedures were more often shortened. Most ROIs postponed or cancelled radiation treatment for benign indications (88.1%). The occurrence of SARS-CoV­2 infections did not affect the treatment options for curative procedures. Non-university-based ROIs seemed to be more willing to change their treatment options for curative and palliative cases than university-based ROIs. CONCLUSION: Most ROIs reported a deep impact of SARS-CoV­2 infections on their work routine. Modification and prioritization of treatment regimens and the application of protective measures preserved a well-functioning radiation oncology service and patient care.

Heart-sparing volumetric modulated arc therapy for whole lung irradiation.

PURPOSE: Whole lung irradiation (WLI) is indicated for subgroups of patients with lung metastases from Wilms' tumor (nephroblastoma). WLI has traditionally been performed with an anterior/posterior field arrangement with poor potential for heart sparing; thus, new techniques are desirable to achieve a lower dose to the heart. MATERIALS AND METHODS: We utilized volumetric modulated arc therapy (VMAT) for WLI with 18 Gy in a patient with metastatic nephroblastoma. The planning results were compared against a three-dimensional (3D) conformal plan. RESULTS: VMAT resulted in adequate target volume coverage with the prescribed dose. Mean heart dose was 10.2 Gy. The dose to organs at risk (OAR) was generally more favorable with VMAT when compared with a 3D-conformal radiotherapy plan. DISCUSSION: WLI with VMAT provides superior sparing of OARs and especially a considerably lower dose to the heart.

Salvage radiotherapy for macroscopic local recurrences after radical prostatectomy : A national survey on patterns of practice.

INTRODUCTION: Although salvage radiotherapy (SRT) for PSA recurrence after radical prostatectomy provides better oncological outcomes when delivered early, in the absence of detectable disease many patients are treated for macroscopic locally recurrent tumors. Due to limited data from prospective studies, we hypothesized an important variability in the SRT management of these patients. Our aim was to investigate current practice patterns of SRT for local macroscopic recurrence after radical prostatectomy. MATERIAL AND METHODS: A total of 14 Swiss radiation oncology centers were asked to complete a survey on treatment specifications for macroscopic locally recurrent disease including information on pretherapeutic diagnostic procedures, dose prescription, radiation delivery techniques and androgen deprivation therapy (ADT). Treatment recommendations on ADT were analyzed using the objective consensus methodology. RESULTS: The majority of centers recommended pretreatment magnetic resonance imaging (MRI) of the pelvis and choline positron emission tomography (PET). The median prescribed dose to the prostate bed was 66 Gy (range 65-72 Gy) with a boost to the macroscopic lesion used by 79% of the centers with a median total dose of 72 Gy (range 70-80 Gy). Intensity-modulated rotational techniques were used by all centers and daily cone beam computed tomography (CT) was recommended by 43%. The use of concomitant ADT for any macroscopic recurrence was recommended by 43% of the centers while the remaining centers recommended it only for high-risk disease, which was not consistently defined. CONCLUSION: We observed a high variability of treatment paradigms when SRT is indicated for macroscopic local recurrences after prostatectomy. These data reflect the need for more standardized approaches and ultimately further research in this field.

Treatment of limited disease small cell lung cancer: the multidisciplinary team.

Small cell lung cancer (SCLC) presents multiple interdisciplinary challenges with several paradigm shifts in its treatment in recent years. SCLC treatment requires multidisciplinary management and timely treatment. The aim of this review is to focus on the team management aspects in the treatment of limited disease SCLC and how this can contribute towards improving outcomes.

Importance and outcome relevance of central pathology review in prostatectomy specimens: data from the SAKK 09/10 randomized trial on prostate cancer.

OBJECTIVE: To conduct a central pathology review within a randomized clinical trial on salvage radiation therapy (RT) in the presence of biochemical recurrence after prostatectomy to assess whether this results in changes in histopathological prognostic factors, such as Gleason score. PATIENTS AND METHODS: A total of 350 patients were randomized and specimens from 279 patients (80%) were centrally reviewed by a dedicated genitourinary pathologist. Gleason score, tumour classification and resection margin status were reassessed and compared with the results of local pathology review. Agreement was assessed using contingency tables and Cohen's kappa coefficient. The association between other histopathological features (e.g. largest diameter of carcinoma) and rapid biochemical progression (up to 6 months after salvage RT) was also investigated. RESULTS: There was good concordance between central and local pathology review for seminal vesicle invasion (pT3b: 91%; κ = 0.95 [95% confidence interval {CI} 0.89, 1.00]), extraprostatic extension (pT3a/b: 94%; κ = 0.82 [95% CI 0.75, 0.89]) and positive surgical margin (PSM) status (87%; κ = 0.7 [95% CI 0.62, 0.79]). The rate of agreement was lower for Gleason score (78%; κ = 0.61 [95% CI 0.52, 0.70]). The median (range) largest diameter of carcinoma was 16 (3-38) mm. A total of 49 patients (18%) experienced rapid biochemical progression after salvage RT. Largest diameter of carcinoma (odds ratio [OR] 2.04 [95% CI 1.30, 3.20]; P = 0.002), resection margin status (OR 0.36 [95% CI 0.18, 0.72]; P = 0.004) and Gleason score (OR 1.55 [95% CI 1.00, 2.42]; P = 0.05) remained associated with rapid progression after salvage RT after backward selection. CONCLUSION: The results of the central pathology analyses showed concordance between central and local pathology review with regard to seminal vesicle invasion, extraprostatic extension and PSM status, but a lower rate of agreement for Gleason score. Largest diameter of carcinoma was found to be a potential prognostic factor for rapid biochemical progression after salvage RT.

Consensus and differences in primary radiotherapy for localized and locally advanced prostate cancer in Switzerland: A survey on patterns of practice.

INTRODUCTION: External beam radiotherapy (EBRT), with or without androgen deprivation therapy (ADT), is an established treatment option for nonmetastatic prostate cancer. Despite high-level evidence from several randomized trials, risk group stratification and treatment recommendations vary due to contradictory or inconclusive data, particularly with regard to EBRT dose prescription and ADT duration. Our aim was to investigate current patterns of practice in primary EBRT for prostate cancer in Switzerland. MATERIALS AND METHODS: Treatment recommendations on EBRT and ADT for localized and locally advanced prostate cancer were collected from 23 Swiss radiation oncology centers. Written recommendations were converted into center-specific decision trees, and analyzed for consensus and differences using a dedicated software tool. Additionally, specific radiotherapy planning and delivery techniques from the participating centers were assessed. RESULTS: The most commonly prescribed radiation dose was 78 Gy (range 70-80 Gy) across all risk groups. ADT was recommended for intermediate-risk patients for 6 months in over 80 % of the centers, and for high-risk patients for 2 or 3 years in over 90 % of centers. For recommendations on combined EBRT and ADT treatment, consensus levels did not exceed 39 % in any clinical scenario. Arc-based intensity-modulated radiotherapy (IMRT) is implemented for routine prostate cancer radiotherapy by 96 % of the centers. CONCLUSION: Among Swiss radiation oncology centers, considerable ranges of radiotherapy dose and ADT duration are routinely offered for localized and locally advanced prostate cancer. In the vast majority of cases, doses and durations are within the range of those described in current evidence-based guidelines.

Phase Ib study evaluating a self-adjuvanted mRNA cancer vaccine (RNActive®) combined with local radiation as consolidation and maintenance treatment for patients with stage IV non-small cell lung cancer.

BACKGROUND: Advanced non-small cell lung cancer (NSCLC) represents a significant unmet medical need. Despite advances with targeted therapies in a small subset of patients, fewer than 20% of patients survive for more than two years after diagnosis. Cancer vaccines are a promising therapeutic approach that offers the potential for durable responses through the engagement of the patient's own immune system. CV9202 is a self-adjuvanting mRNA vaccine that targets six antigens commonly expressed in NSCLC (NY-ESO-1, MAGEC1, MAGEC2, 5 T4, survivin, and MUC1). METHODS/DESIGN: The trial will assess the safety and tolerability of CV9202 vaccination combined with local radiation designed to enhance immune responses and will include patients with stage IV NSCLC and a response or stable disease after first-line chemotherapy or therapy with an EGFR tyrosine kinase inhibitor. Three histological and molecular subtypes of NSCLC will be investigated (squamous and non-squamous cell with/without EGFR mutations). All patients will receive two initial vaccinations with CV9202 prior to local radiotherapy (5 GY per day for four successive days) followed by further vaccinations until disease progression. The primary endpoint of the study is the number of patients experiencing Grade >3 treatment-related adverse events. Pharmacodynamic analyses include the assessment of immune responses to the antigens encoded by CV9202 and others not included in the panel (antigen spreading) and standard efficacy assessments. DISCUSSION: RNActive self-adjuvanted mRNA vaccines offer the potential for simultaneously inducing immune responses to a wide panel of antigens commonly expressed in tumors. This trial will assess the feasibility of this approach in combination with local radiotherapy in NSCLC patients. TRIAL REGISTRATION: Clinicaltrials.gov: NCT01915524/EudraCT No.: 2012-004230-41.

[Is there an indication for local treatment in metastasised hormone-sensitive prostate cancer?] / Gibt es eine Indikation zur Lokaltherapie des mHSPC?

In case of newly diagnosed metastasised hormone-sensitive prostate cancer, there are two indications for local treatment: to reduce or avoid local symptoms thus improving quality of life and prolonging survival in a subset of patients. Local treatment must be seen in a multimodal treatment approach and is not a replacement of systemic treatment. In the following review, we highlight the current literature for the different local treatment options, radiotherapy and radical prostatectomy, and try to give indications for which option should be offered to which patient.

Erectile function preservation after salvage radiation therapy for biochemically recurrent prostate cancer after prostatectomy: Five-year results of the SAKK 09/10 randomized phase 3 trial.

Objectives: To evaluate effects of dose intensified salvage radiotherapy (sRT) on erectile function in biochemically recurrent prostate cancer (PC) after radical prostatectomy (RP). Materials and methods: Eligible patients had evidence of biochemical failure after RP and a PSA at randomization of ≤ 2 ng/ml. Erectile dysfunction (ED) was investigated as secondary endpoint within the multicentre randomized trial (February 2011 to April 2014) in patients receiving either 64 Gy or 70 Gy sRT. ED and quality of life (QoL) were assessed using CTCAE v4.0 and the EORTC QoL questionnaires C30 and PR25 at baseline and up to 5 years after sRT. Results: 344 patients were evaluable. After RP 197 (57.3 %) patients had G0-2 ED while G3 ED was recorded in 147 (42.7 %) patients. Subsequently, sexual activity and functioning was impaired. 5 years after sRT, 101 (29.4 %) patients noted G0-2 ED. During follow-up, 44.2 % of patients with baseline G3 ED showed any improvement and 61.4 % of patients with baseline G0-2 ED showed worsening. Shorter time interval between RP and start of sRT (p = 0.007) and older age at randomization (p = 0.005) were significant predictors to more baseline ED and low sexual activity in the long-term. Age (p = 0.010) and RT technique (p = 0.031) had a significant impact on occurrence of long-term ED grade 3 and worse sexual functioning. During follow-up, no differences were found in erectile function, sexual activity, and sexual functioning between the 64 Gy and 70 Gy arm. Conclusion: ED after RP is a known long-term side effect with significant impact on patients' QoL. ED was further affected by sRT, but dose intensification of sRT showed no significant impact on erectile function recovery or prevalence of de novo ED after sRT. Age, tumor stage, prostatectomy and RT-techniques, nerve-sparing and observation time were associated with long-term erectile function outcome.ClinicalTrials.gov. Identifier: NCT01272050.

Dose escalation for stereotactic arrhythmia radioablation of recurrent ventricular tachyarrhythmia - a phase II clinical trial.

BACKGROUND: Stereotactic arrhythmia radioablation (STAR) is delivered with a planning target volume (PTV) prescription dose of 25 Gy, mostly to the surrounding 75-85% isodose line. This means that the average and maximum dose received by the target is less than 35 Gy, which is the minimum threshold required to create a homogenous transmural fibrosis. Similar to catheter ablation, the primary objective of STAR should be transmural fibrosis to prevent heterogenous intracardiac conduction velocities and the occurrence of sustained ventricular arrhythmias (sVA) caused by reentry. We hypothesize that the current dose prescription used in STAR is inadequate for the long-term prevention of sVA and that a significant increase in dose is necessary to induce transmural scar formation. OBJECTIVE: A single arm, multi-center, phase II, dose escalation prospective clinical trial employing the i3 + 3 design is being conducted to examine the safety of a radiation dose-escalation strategy aimed at inducing transmural scar formation. The ultimate objective of this trial is to decrease the likelihood of sVA recurrence in patients at risk. METHODS: Patients with ischemic or non-ischemic cardiomyopathy and recurrent sVA, with an ICD and history of ≥ 1 catheter ablation for sVA will be included. This is a prospective, multicenter, one-arm, dose-escalation trial utilizing the i3 + 3 design, a modified 3 + 3 specifically created to overcome limitations in traditional dose-finding studies. A total of 15 patients will be recruited. The trial aims to escalate the ITV dose from 27.0 Gy to an ITV prescription dose-equivalent level of maximum 35.1 Gy by keeping the PTV prescription dose constant at 25 Gy while increasing the dose to the target (i.e. the VT substrate without PTV margin) by step-wise reduction of the prescribing isodose line (85% down to 65%). The primary outcome of this trial is safety measured by registered radiation associated adverse events (AE) up to 90 days after study intervention including radiation associated serious adverse events graded as at least 4 or 5 according to CTCAE v5, radiation pneumonitis or pericarditis requiring hospitalization and decrease in LVEF ≥ 10% as assessed by echocardiography or cardiac MRI at 90 days after STAR. The sample size was determined assuming an acceptable primary outcome event rate of 20%. Secondary outcomes include sVA burden at 6 months after STAR, time to first sVA recurrence, reduction in appropriate ICD therapies, the need for escalation of antiarrhythmic drugs, non-radiation associated safety and patient reported outcome measures such as SF-36 and EQ5D. DISCUSSION: DEFT-STAR is an innovative prospective phase II trial that aims to evaluate the optimal radiation dose for STAR in patients with therapy-refractory sVA. The trial has obtained IRB approval and focuses on determining the safe and effective radiation dose to be employed in the STAR procedure. TRIAL REGISTRATION: NCT05594368.