An observational study in Type II Endoleak and Abdominal Aortic Aneurysm Enlargement, sponsored by Ente Ospedaliero Cantonale, Bellinzona. Not yet recruiting. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-11.
Sponsored by Ente Ospedaliero Cantonale, Bellinzona · Observational
Background and rationale:
Abdominal aortic aneurysm (AAA) is a weakening and enlargement of the main artery in the abdomen. Endovascular aneurysm repair (EVAR) is a minimally invasive treatment used to repair an AAA. After EVAR, some patients develop a complication, called a type II endoleak (T2EL), in which blood continues to flow into the aneurysm sac through small blood vessels. Many T2ELs disappear on their own, but in some patients they can cause the aneurysm sac to enlarge and may require another procedure. The RADAR study aims to develop a deep-learning computer model that can use the CT scan performed before EVAR to predict which patients are more likely to develop a T2EL associated with aneurysm enlargement. The model will be developed using information from several hospitals and tested on patients from hospitals that were not involved in its development.
Duration: July 2026 - December 2028
The study will include patients who have undergone EVAR between 1 January 2015 and 31 December 2025. Their available follow-up information will be collected until 31 December 2026 or until an earlier event such as the last available CT scan, a procedure related to T2EL, another defined medical event, or death. The baseline postoperative CTA, acquired 1-3 months after EVAR, will serve as the reference examination for assessment of aneurysm-sac growth during follow-up. Patients who have not developed the study outcome generally need at least 24 months of imaging follow-up to be classified reliably.
Objectives:
The primary objective is to develop and test a deep-learning model that can predict, before EVAR, whether a patient will develop a T2EL and whether it will be associated with significant enlargement of the aneurysm sac. The model will be tested using data from hospitals that were not involved in its development. Secondary objectives are to assess whether the model works consistently across different hospitals and CT scanning methods; compare the new model with the original NornirNet model; determine whether adding clinical and anatomical information improves the predictions; assess differences in performance between hospitals; and evaluate how well the model's predicted risks correspond to the outcomes actually observed.
Study population:
The study is a multicenter observational study involving patients over the age of 18 who underwent elective EVAR for an intact fusiform abdominal aortic aneurysm at participating hospitals in Switzerland, Europe, and the United States between 2015 and 2025. Patients must have suitable CT scans before and after EVAR and sufficient medical and imaging information to determine whether a T2EL occurred and how the aneurysm changed over time. Patients treated for a ruptured aneurysm, patients with certain other types of aneurysms, patients who had previous aortic procedures, and patients whose CT scans are not suitable for analysis will be excluded. The planned study population is approximately 1,250 patients, depending on the number of eligible patients available at the participating hospitals.
Study procedures:
This is a retrospective study, meaning that it uses information and CT scans that were already collected as part of routine medical care. No additional examinations or procedures are performed for the study, and no biological samples are collected. Participating hospitals will provide coded clinical information and anonymized CT scans. The information collected may include age, sex, other medical conditions, body weight and height, laboratory results, heart-related information, details about the aneurysm and blood vessels, and information about the EVAR procedure. Follow-up CT scans will be reviewed by specialists to determine whether a T2EL occurred and whether the aneurysm sac became larger. Patients will be classified into three groups: those with no T2EL, those with a T2EL without significant aneurysm enlargement, and those with a T2EL associated with aneurysm enlargement of at least 5 mm or a related additional procedure. The deep-learning model will be developed using data from some participating hospitals and then tested on data from other hospitals that were not involved in developing the model. Its ability to make accurate and consistent predictions will then be evaluated.
RADAR is a retrospective multicenter observational study designed to develop and independently evaluate a three-dimensional deep-learning model for preoperative prediction of clinically relevant type II endoleak (T2EL) after endovascular aneurysm repair (EVAR).
The model will be developed using preoperative CTA data from designated development centers. Model fitting, hyperparameter tuning, and selection of operating thresholds will be performed exclusively within these centers using center-aware cross-validation. After completion of development, the model architecture, parameters, and operating thresholds will be frozen before evaluation on independent held-out test centers. Data from these centers will not be used for model development, tuning, or threshold selection.
The primary analysis will assess the ability of the frozen model to distinguish three predefined clinical outcome classes based on the occurrence of T2EL and subsequent aneurysm-sac behavior. This center-level separation between development and testing is intended to provide an estimate of model performance and generalizability across institutions and heterogeneous imaging protocols.
Secondary analyses will assess inter-center variability in performance, model calibration, and the incremental predictive value of clinical and anatomical variables. The newly developed model will also be compared with the original NornirNet model on a separate common dataset reserved specifically for this comparison.
467 studies on the registry are indexed under Aortic Aneurysm, Abdominal; 99 are open to participants now.
This study's planned enrollment of 1,250 is above the median of 165 across 217 observational studies indexed under Aortic Aneurysm, Abdominal.
Browse Aortic Aneurysm, Abdominal studies →Ente Ospedaliero Cantonale, Bellinzona is the lead sponsor of 38 studies on the registry; 17 are open to participants now.
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The study includes a retrospective multicenter cohort of approximately 1,250 adult patients (≥18 years) who underwent elective standard EVAR for an intact fusiform infrarenal abdominal aortic aneurysm between 01.01.2015 and 31.12.2025. Patients must have available preoperative and postoperative CT angiography (CTA) scans of sufficient quality and adequate follow-up data. Patients will be excluded if they underwent emergency repair for ruptured aneurysm, had non-fusiform aneurysms, previous aortic interventions, complex EVAR procedures, non-diagnostic imaging, or refused the use of their health data for research where applicable. Patients will be classified according to follow-up findings into three outcome classes: Class 0, no type II endoleak; Class 1, type II endoleak without significant aneurysm sac growth; or Class 2, type II endoleak with significant sac growth or T2EL-related reintervention.
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Eligibility is defined by the inclusion and exclusion criteria below. Conditions that depend on the study outcome (occurrence of type II endoleak, competing endoleak types, and duration of imaging follow-up) are deliberately not treated as eligibility criteria; they are specified separately as analysis-set, outcome-classification and censoring rules, in order to avoid outcome-dependent selection bias. The minimum duration of imaging follow-up specified in the section "Outcome classification and follow-up requirement" is a requirement for valid assignment of the reference outcome class and applies only to the event-free classes, for which the absence of the outcome can be established only by a sufficient period of observation. It does not apply to patients in whom the outcome has already been documented.
Inclusion criteria
Treatment by standard EVAR, defined as implantation of a commercially available bifurcated infrarenal stent-graft with proximal sealing in the infrarenal neck, below the lowermost renal artery, and without any of the following:
Exclusion criteria
Handling of competing endoleak types (analysis-set and censoring rule) The occurrence of a type I, III, IV or V endoleak is not an eligibility criterion but a censoring or competing event, adjudicated as follows.
Outcome classification and follow-up requirement (analysis-set rule)
The primary outcome is a three-class variable adjudicated over the entire available imaging follow-up. Each patient is assigned to exactly one of the following classes:
Because Class 2 requires two sequential events (appearance of the endoleak and subsequent sac growth), whereas Classes 0 and 1 are defined by the sustained absence of an event, the minimum duration of imaging follow-up required for a valid class assignment differs by class. This is a label-ascertainment (outcome-adjudication) requirement, applied to ensure the validity of the reference standard against which the model is evaluated. It is not an eligibility criterion. The minimum follow-up requirement applies only to event-free patients (Classes 0 and 1), whereas patients in whom a Class 2 event has already been documented are assigned to Class 2 irrespective of the total duration of follow-up. It is not applied in an outcome-dependent manner that would preferentially remove patients at higher risk of the outcome. Class 2 (malignant): no minimum duration of follow-up is required. Once sac growth ≥ 5 mm attributable to a type II endoleak, or a T2EL-related reintervention, has been documented, the class assignment is definitive irrespective of the total duration of follow-up. Excluding such patients on the basis of short follow-up would remove confirmed events and would introduce outcome-dependent selection.
All eligible patients enter the cohort at the baseline (1-3 month) postoperative CTA and are followed until the earliest of: the last available CTA, a T2EL-related secondary intervention, a censoring event as defined in the preceding section, death, or administrative censoring at 31 December 2026. Administrative censoring at 31 December 2026 is a common closing date applied to the entire cohort and not a deadline by which follow-up must already have ended: a patient still under observation on that date contributes person-time up to that date, whereas a patient whose follow-up ends earlier for any of the reasons listed above is censored at the earlier date. The number of patients censored for each reason will be reported.
Reproducibility of the diameter measurement on which the 5 mm threshold depends will be quantified. A random sample of at least 10% of examinations will be measured independently by two readers, and the intraclass correlation coefficient together with the Bland-Altman limits of agreement for maximum aneurysm diameter will be reported. Cases in which the measured diameter change lies within the limits of agreement of the 5 mm threshold will be identified and examined in a sensitivity analysis.
Variables recorded rather than applied as eligibility criteria The following are documented as covariates and are not used to exclude patients, since retrospective adjudication would be unreliable and would preferentially remove patients with hostile anatomy, in whom type II endoleak behavior may differ.
This retrospective multicenter observational cohort includes adult patients who underwent elective standard EVAR for an intact fusiform infrarenal abdominal aortic aneurysm between 01.01.2015 and 31.12.2025 at participating centers. Eligible patients are identified according to predefined inclusion and exclusion criteria. Based on imaging follow-up, patients with sufficient information for outcome adjudication are assigned to one of three classes: Class 0, no type II endoleak (T2EL); Class 1, T2EL without significant aneurysm sac growth; or Class 2, T2EL associated with significant sac growth or T2EL-related reintervention. Eligible patients with insufficient follow-up for reliable outcome-class assignment are classified as indeterminate, retained in the study database, and excluded from the primary analysis.
Other: Artificial intelligence model analyzing preoperative CT angiography
This study involves the retrospective multicenter analysis of preoperative CT angiography (CTA) and clinical data from patients who underwent EVAR. A new and improved three-dimensional deep-learning model, building on the NornirNet framework, will be developed using data from designated development centers and subsequently evaluated, after model freezing, on independent held-out centers.
Performance of the deep-learning model in held-out test centers
Performance of the frozen deep-learning model will be evaluated in independent held-out test centers for three-class prediction of T2EL outcome: Class 0 (no T2EL), Class 1 (T2EL without significant aneurysm sac growth), and Class 2 (T2EL with significant sac growth or T2EL-related reintervention). Discrimination and classification performance will be assessed using prespecified performance metrics, including AUC, sensitivity, and specificity.
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
AUC comparison of the deep-learning models
Comparison of the newly developed deep-learning model with the original NornirNet model on the reserved common comparison dataset using the area under the receiver operating characteristic curve (AUC).
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Sensitivity comparison of the deep-learning models
Comparison of the newly developed deep-learning model with the original NornirNet model on the reserved common comparison dataset using sensitivity.
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Specificity comparison of the deep-learning models
Comparison of the newly developed deep-learning model with the original NornirNet model on the reserved common comparison dataset using specificity.
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Inter-center variability in AUC
Assessment of inter-center variability in model performance across held-out test centers using the area under the receiver operating characteristic curve (AUC).
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Inter-center variability in specificity
Assessment of inter-center variability in model performance across held-out test centers using specificity.
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Change in AUC with clinical and anatomical variables
Assessment of the incremental predictive value of clinical and anatomical variables using change in the area under the receiver operating characteristic curve (AUC).
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Net Benefit with clinical and anatomical variables
Assessment of the incremental predictive value of clinical and anatomical variables using Decision Curve Analysis (Net Benefit).
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
Brier score for model calibration
Assessment of model calibration using the Brier score.
Time frame: From the baseline postoperative CTA (1-3 months after EVAR) through the last available follow-up, T2EL-related reintervention, censoring event, death, or administrative censoring on 31 December 2026.
No study locations are listed for this record.
Plan to share: No — The data generated and analyzed during this study will not be publicly available due to privacy and data protection regulations. Study data will be collected and pseudonymized according to applicable ethical and regulatory requirements and institutional data-sharing agreements.
Start is estimated for Oct 2026; primary completion for Dec 2027, 14 months later.
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Ente Ospedaliero Cantonale, Bellinzona