129 research outputs found
19-0097_Supplement_A – Supplemental material for A New Methodology to Determine Apposition, Dilatation, and Position of Endografts in the Descending Thoracic Aorta After Thoracic Endovascular Aortic Repair
No full textSupplemental material, 19-0097_Supplement_A for A New Methodology to Determine Apposition, Dilatation, and Position of Endografts in the Descending Thoracic Aorta After Thoracic Endovascular Aortic Repair by Kim van Noort, Richte C. L. Schuurmann, Gersom Post Hospers, Emma van der Weijde, Hans G. Smeenk, Robin H. Heijmen and Jean-Paul P. M. de Vries in Journal of Endovascular Therapy</p
A verification study on the accuracy of virtual thoracic endovascular aneurysm repair procedure
No full textComputational models in the cardiovascular field, among which in Thoracic Endovascular Aneurysm Repair (TEVAR)—which involves the deployment of a stent-graft to exclude pathological region of the aorta from circulation—are gaining interest among clinicians as tools to support pre-operative decision-making. To assess the credibility of in-silico models, the American Society of Mechanical Engineers published the V&V40 framework, which includes verification, validation, and uncertainty quantification. This study presents a verification analysis of TEVAR simulations to evaluate the impact of selected parameters on simulation outcomes, focusing on specific quantities of interests. Simulations were conducted on three patient-specific anatomies replicating the crimping, tracking, and release phases of the clinical procedure. Evaluated numerical parameters included mass damping, friction coefficient, tracking velocity, and release time. Sliding distance, rotation and computational time were analyzed in the tracking phase; while Opening Area, center-to-center distance, and plane rotation were evaluated in the release phase, comparing simulation results with post-operative CT segmentations. A mass damping coefficient of 0.1 ms−1 for the stent-graft and 1 ms−1 for the catheter, a friction coefficient of 1 between stent-graft and catheter, and a velocity of 0.5 m/s yielded the best results during tracking. In the release phase, the selected parameters were: a damping of 0.1 ms−1, a friction coefficient of 0.1, and a release time of 5 ms. In conclusion, this study provides a comprehensive analysis to support the selection of best settings for TEVAR simulations. A verification analysis is essential to understand the influence of numerical parameters on simulation outcomes
Modeling geometrical uncertainties for radiotherapy plan optimization without margins
No full textRadiotherapy is one of the methods used to treat cancer. One common approach for radiotherapy is exposing the patient to external beams of high-energy X-ray photons. Using the intensity-modulated radiation therapy (IMRT) technique, the fluence (radiation energy per unit area) of the radiation beams can be modulated to optimally shape the 3D high-dose volume to the tumor shape. The term radiotherapy will henceforward refer to this technique. Before radiotherapy can be administered, a treatment plan must be generated to accomplish high tumor-dose and maximum sparing of surrounding healthy tissues. This planning is usually based on a computer-tomography (CT) scan showing the tumor and healthy organs-of-interest, called the planning CT scan. The treatment itself is normally given in several fractions over several days (e.g. about 40 for prostate cancer), where for each fraction a proportional part of the dose is given. Due to movements and deformations, the geometrical positions of the organs in the body at the time of the treatment sessions might not be the same as in the planning CT scan. These geometrical uncertainties can make radiation beams miss the target (the tumor site, usually called the clinical target volume, CTV), making the actually delivered dose in the CTV less than what is prescribed. So, eradication of the tumor may fail. To prevent this, the irradiated area is usually enlarged with a margin, following a margin recipe. Although using a margin recipe can prevent underdosage in the CTV, unfortunately it can also potentially harm the healthy organs-at-risk (OAR) around the CTV. The larger the margin, the higher the probability of damaging the OAR. The aim of this thesis is to develop a method to calculate the optimized fluence profiles of the radiation beams, while taking into account the geometrical uncertainties. The irradiated area will also be enlarged as with the margin-recipe, but now more locally adapted to the movements and deformations of the organs, sparing the OAR as much as possible, while delivering a high enough dose to the CTV. In this thesis, the movements and deformations are first modeled for a whole patient population. Then a useful method is described with which in this uncertain geometry the expected radiation dose and its corresponding variance can be calculated. Finally the corresponding radiation plan is optimized. The first step is to model the movements and deformations of the organs. For this, a method called principal component analysis (PCA) has been used, which extracts the dominant modes of movements of the voxels (the volume discretization units) of the organs, as well as estimating their probabilities. Unfortunately PCA can usually not be done directly to a new patient because there is generally just one CT scan (or at most a few) available for this patient, which gives not enough data on movements and deformations. Therefore in this thesis a scheme for combining the movement data for the organs of interest from a population of patients has been developed, and tested for a prostate cancer site. PCA has then been applied to the resulting database, and it turns out that the dominant modes have plausible physical explanations. Further verification has been obtained by carrying out an error analysis, which shows that the dominant modes are also shared by prostates which are not included in the database. The movements and deformations have been used to calculate the expected value (mean) and the variance of the dose. To do this, an integration over the probability space is needed, which is computationally expensive. If the mean and the variance of the dose are going to be used in the objective functions and constraints of the fluence optimization, they have to be calculated for every optimization iteration. To shift the burden of probability integrations away from the optimization iterations, dynamic dose deposition matrices have been developed. Multiplication of these matrices with the fluence profile vectors gives the expected value and variance of the voxel doses. The dynamic dose deposition matrices also help to calculate the derivatives of the expected value and the variance of the dose with respect to the fluencies. These derivatives are usually needed in optimizers, such as Erasmus-iCycle (an optimization suite developed in Erasmus MC Cancer Institute in Rotterdam, The Netherlands), which is used in this thesis. Numerical derivations without dynamic dose deposition matrices, for example using the Monte Carlo method, are computationally expensive, especially since the derivatives must be calculated for each optimization iteration as well. Once the dynamic dose deposition matrices are calculated, inclusion of the expected value and the variance of the doses in the fluence optimization algorithm (called here dynamic optimization) is computationally as costly as the usual fluence optimization (called static optimization). In this thesis, dynamic optimization is done by substituting the dose (in static optimization) with the expected value of the dose in the objective functions and constraints. The variance is included in the form of the average of the voxel variances. The preprocessing effort to calculate the average of the variances is much less than to calculate the variances at every voxel separately. In Erasmus-iCycle, the formulation of the optimization criteria is done using a wish-list. There the objective functions (costlets) are ranked according to their priorities, and each costlet has its own goal. For example for a prostate CTV, a costlet for dynamic optimization can be to maximize the mean dose (expected dose), with the goal of 78 Gy. In the wish-list, some hard constraints are also prescribed, e.g. the minimum mean dose in the prostate CTV can be 74.1 Gy (95% of 78 Gy). Using an optimization method called 2p?c, the costlets are optimized with respect to the constraints in two steps, so that a Pareto-optimal solution is obtained, where no improvement of a costlet can be made without deteriorating the others. To evaluate the results of the fluence optimization, a new evaluation tool called dose probability volume histogram (DPVH) is introduced in this thesis to complement the conventional dose volume histogram (DVH). While in dynamic optimization the DVH depicts the volume percentage of the organ that receives a certain expected dose, the DPVH shows the probability that the delivered dose in the organ actually fulfills the optimization criteria. Dynamic optimization using the dynamic deposition matrices has been tested for a simple cubic geometry and a prostate case. The results show that the margin-recipe solution prescribes a larger irradiated area for the same DVH in the CTV compared to dynamic optimization using expected values of the doses. Consequently using expected doses in the dynamic optimization damages the OAR less than the margin-recipe solution. Adding costlets on the average value of the variances improves the DVH and DPVH for the CTV. Unfortunately our results are not yet conclusive for the OAR in this case. It has further been shown though, that the local movements are even more taken into account, when the variances are included.Delft Institute of Applied Mathematics (DIAM)Electrical Engineering, Mathematics and Computer Scienc
Thoracic Stent Graft Numerical Models To Virtually Simulate Thoracic Endovascular Aortic Repair: A Scoping Review
No full textContains fulltext :
300938.pdf (Publisher’s version ) (Open Access)OBJECTIVE: Pre-procedural planning of thoracic endovascular aortic repair (TEVAR) may implement computational adjuncts to predict technical and clinical outcomes. The aim of this scoping review was to explore the currently available TEVAR procedure and stent graft modelling options. DATA SOURCES: PubMed (MEDLINE), Scopus, and Web of Science were systematically searched (English language, up to 9 December 2022) for studies presenting a virtual thoracic stent graft model or TEVAR simulation. REVIEW METHODS: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) was followed. Qualitative and quantitative data were extracted, compared, grouped, and described. Quality assessment was performed using a 16 item rating rubric. RESULTS: Fourteen studies were included. Among the currently available in silico simulations of TEVAR, severe heterogeneity exists in study characteristics, methodological details, and evaluated outcomes. Ten studies (71.4%) were published during the last five years. Eleven studies (78.6%) included heterogeneous clinical data to reconstruct patient specific aortic anatomy and disease (e.g., type B aortic dissection, thoracic aortic aneurysm) from computed tomography angiography imaging. Three studies (21.4%) constructed idealised aortic models with literature input. The applied numerical methods consisted of computational fluid dynamics analysing aortic haemodynamics in three studies (21.4%) and finite element analysis analysing structural mechanics in the others (78.6%), including or excluding aortic wall mechanical properties. The thoracic stent graft was modelled as two separate components (e.g., graft, nitinol) in 10 studies (71.4%), as a one component homogenised approximation (n = 3, 21.4%), or including nitinol rings only (n = 1, 7.1%). Other simulation components included the catheter for virtual TEVAR deployment and numerous outcomes (e.g., Von Mises stresses, stent graft apposition, drag forces) were evaluated. CONCLUSION: This scoping review identified 14 severely heterogeneous TEVAR simulation models, mostly of intermediate quality. The review concludes there is a need for continuous collaborative efforts to improve the homogeneity, credibility, and reliability of TEVAR simulations.01 december 202
On the validation of patient-specific numerical simulations of the TEVAR procedure
No full textThe Thoracic Endovascular Aortic Repair (TEVAR) is becoming the first choice to treat thoracic aortic pathologies (e.g., aneurysms, ulcerations, and dissections) in a minimally invasive way. It consists of placing a self-expandable stent-graft into the pathological region to recreate a more physiological condition. When computational models are used in this clinical context to predict procedural results, their credibility should be validated and verified. This works applies a validated finite element methodology to four patient-specific anatomies. Different sizes of a commercial stent-graft model are recreated, and the TEVAR simulation results are validated by comparing them to post-operative Computed Tomography images. Errors between simulation and segmentation are lower than 10% for the stent struts opening area. This study also evaluates and discusses numerical quantities (contact pressures, device-to-vessel distances, and stress distributions) associated with potential TEVAR complications such as device migration and bird beak phenomenon. This work aims at demonstrating how a fully validated methodology is useful for clinicians to identify the best treatment for the patient before the intervention to avoid device-related complications
Determination of the gained proximal sealing zone length after debranching of the left subclavian artery in thoracic endovascular aortic repair.
No full textBACKGROUND: For descending thoracic aortic aneurysms (TAA) in proximity of the aortic arch, debranching of the left subclavian artery (LSA) may be necessary to extend proximal sealing in zone 2. The aim of this study was to determine the added proximal apposition length gained from LSA debranching during thoracic endovascular aortic repair (TEVAR). METHODS: This multicenter retrospective study (2010-2020) included patients who underwent elective TEVAR in zone 2 for a degenerative TAA where the LSA was surgically debranched. The endograft position on the first postoperative computed tomography angiography (CTA) scan was assessed using post-processing software. The analysis included the shortest apposition length (SAL), the tilt of the proximal edge of the endograft, and the distance between the endograft and the left common carotid artery. Clinical endpoints (neurological complications and endoleaks) at 30 days were also reported. RESULTS: Twenty-two patients were included. The median interval between TEVAR and the first postoperative CTA was 3 days (2-10 days). Median SAL was 9.2 mm (1.3-26.4 mm), of which 8.6 mm (1.3-16.2 mm) was gained proximal of the LSA, including the LSA orifice. In 12 patients (55.5%) the SAL was <10 mm. The median tilt was 18.3° (13.9°-22.2°). Seven endoleaks were reported on the first CTA: 1 type Ia, 2 type Ib, 3 type II, and 1 type III. CONCLUSIONS: Debranching the LSA adds valuable sealing length in zone 2, but the SAL was still relatively short in many patients, putting these patients at risk for a future type Ia endoleak. Accurate assessment of the circumferential apposition on postoperative CTA follow-up in these high-risk patients with short, complex landing zones seems mandatory. Evaluation of apposition in a larger population with longer follow-up is advised
Acute management of aortobronchial and aortoesophageal fistulas using thoracic endovascular aortic repair
No full textBackgroundAortobronchial fistula (ABF) and aortoesophageal fistula (AEF) are rare but lethal if untreated; open thoracic surgery is associated with high operative mortality and morbidity. In this case series, we sought to investigate outcomes of thoracic endovascular aortic repair (TEVAR) for emergency cases of ABF and AEF.MethodsWe retrospectively reviewed all patients with AEF and ABF undergoing TEVAR in three European teaching hospitals between 2000 and January 2009. Eleven patients were identified including 6 patients with ABF, 4 patients with AEF, and 1 patient with a combined ABF and AEF. In-hospital outcomes and follow-up after TEVAR were evaluated.ResultsMedian age was 63 years (interquartile range, 31); 8 were male. Ten patients presented with hemoptysis or hematemesis; 4 developed hemorrhagic shock. All patients underwent immediate TEVAR, and 3 AEF patients required additional esophageal surgery. Five patients died (45%), including 3 patients with AEF, 1 patient with ABF, and 1 patient with a combined ABF and AEF, after a median duration of 22 days (interquartile range, 51 days). The patient with AEF that survived had received early esophageal reconstruction. Causes of death were: sepsis (n = 2), acute respiratory distress syndrome (ARDS) (n = 1), thoracic infections (n = 1), and aortic rupture (n = 1). Median follow-up of surviving patients was 45 months (interquartile range, 45 months). Six additional vascular interventions were performed in 3 survivors.ConclusionTEVAR does prevent immediate exsanguination in patients admitted with AEF and ABF, but after initial deployment of the endograft and control of the hemodynamic status, most patients, in particular those with AEF, are at risk for infectious complications. Early esophageal repair after TEVAR appears to improve the survival in case of AEF. Therefore, TEVAR may serve as a bridge to surgery in emergency cases of AEF with subsequent definitive open operative repair of the esophageal defect as soon as possible. In patients with ABF, additional open surgery may not be necessary after the endovascular procedure
A Feasibility Study of Off-the-Shelf Scalloped Stent-Grafts in Acute Type B Aortic Dissection
No full textPurpose: To evaluate the applicability of an off-the-shelf scalloped stent-graft to preserve left subclavian artery (LSA) flow in thoracic endovascular aortic repair (TEVAR) for acute type B aortic dissection. Methods: The computed tomography angiograms (CTA) of 70 consecutive patients (median age 64 years; 44 men) with acute Stanford type B aortic dissection were retrospectively analyzed to identify patients in whom a short proximal landing zone (<15 mm from the retrogradely dissected wall layers) would require LSA overstenting during TEVAR. A scalloped stent-graft was deemed possible in those patients with the intimal entry tear located at least 20 mm distant from the LSA ostium. Results: The LSA needed to be covered in 56 (80%) patients. Of these, an off-the-shelf scalloped stent-graft would have been applicable in 23 (41%) patients. In the latter group, the median aortic diameter was 31 mm (range 26-37), the median length of the LSA ostium was 13 mm (range 10-20), and the median width of the LSA ostium was 15 mm (range 11-24). Three differently sized off-the-shelf stent-grafts with the largest scallop possible could have adequately treated 20 (36%) of the 56 patients in the acute phase. Conclusion: In this single-center imaging-based study, involvement of the LSA in the setting of acute type B aortic dissection was seen in 80% of patients treated with TEVAR. Three off-the-shelf stent-grafts would suffice to treat one-third of these acute type B aortic dissections and may offer a relatively simple solution to preserve LSA flow, thereby lowering the risk of malperfusion of the (posterior) cerebrum, spinal cord, and left arm in an urgent/emergent setting
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