A Multicenter Pilot Study on the Clinical Utility of Computational Modeling for Flow-Diverter Treatment Planning

BACKGROUND AND PURPOSE

Selection of the correct flow-diverter size is critical for cerebral aneurysm treatment success, but it remains challenging due to the interplay of device size, anatomy, and deployment. Current convention does not address these challenges well. The goals of this pilot study were to determine whether computational modeling improves flow-diverter sizing over current convention and to validate simulated deployments.

MATERIALS AND METHODS

Seven experienced neurosurgeons and interventional neuroradiologists used computational modeling to prospectively plan 19 clinical interventions. In each patient case, physicians simulated 2-4 flow-diverter sizes that were under consideration based on preprocedural imaging. In addition, physicians identified a preferred device size using the current convention. A questionnaire on the impact of computational modeling on the procedure was completed immediately after treatment. Rotational angiography image data were acquired after treatment and compared with flow-diverter simulations to validate the output of the software platform.

RESULTS

According to questionnaire responses, physicians found the simulations useful for treatment planning, and they increased their confidence in device selection in 94.7% of cases. After viewing the simulations results, physicians selected a device size that was different from the original conventionally planned device size in 63.2% of cases. The average absolute difference between clinical and simulated flow-diverter lengths was 2.1 mm. In 57% of cases, average simulated flow-diverter diameters were within the measurement uncertainty of clinical flow-diverter diameters.

CONCLUSIONS

Physicians found computational modeling to be an impactful and useful tool for flow-diverter treatment planning. Validation results showed good agreement between simulated and clinical flow-diverter diameters and lengths.

The effect of PD-L1 testing on the cost-effectiveness and economic impact of immune checkpoint inhibitors for the second-line treatment of NSCLC

Background

Immune checkpoint inhibitors improve outcomes compared with chemotherapy in lung cancer. Tumor PD-L1 receptor expression is being studied as a predictive biomarker. The objective of this study was to assess the cost-effectiveness and economic impact of second-line treatment with nivolumab, pembrolizumab, and atezolizumab with and without the use of PD-L1 testing for patient selection.

Design

We developed a decision-analytic model to determine the cost-effectiveness of PD-L1 assessment and second-line immunotherapy versus docetaxel. The model used outcomes data from randomized clinical trials (RCTs) and drug acquisition costs from the United States. Thereafter, we used epidemiologic data to estimate the economic impact of the treatment.

Results

We included four RCTs (2 with nivolumab, 1 with pembrolizumab, and 1 with atezolizumab). The incremental quality-adjusted life year (QALY) for nivolumab was 0.417 among squamous tumors and 0.287 among non-squamous tumors and the incremental cost-effectiveness ratio (ICER) were $155 605 and $187 685, respectively. The QALY gain in the base case for atezolizumab was 0.354 and the ICER was $215 802. Compared with treating all patients, the selection of patients by PD-L1 expression improved incremental QALY by up to 183% and decreased the ICER by up to 65%. Pembrolizumab was studied only in patients whose tumors expressed PD-L1. The QALY gain was 0.346 and the ICER was $98 421. Patient selection also reduced the budget impact of immunotherapy.

Conclusion

The use of PD-L1 expression as a biomarker increases cost-effectiveness of immunotherapy but also diminishes the number of potential life-years saved.

Hemodynamic characterization of geometric cerebral aneurysm templates

Hemodynamics are currently considered to a lesser degree than geometry in clinical practices for evaluating cerebral aneurysm (CA) risk and planning CA treatment. This study establishes fundamental relationships between three clinically recognized CA geometric factors and four clinically relevant hemodynamic responses. The goal of the study is to develop a more combined geometric/hemodynamic basis for informing clinical decisions. Flows within eight idealized template geometries were simulated using computational fluid dynamics and measured using particle image velocimetry under both steady and pulsatile flow conditions. The geometric factor main effects were then analyzed to quantify contributions made by the geometric factors (aneurysmal dome size (DS), dome-to-neck ratio (DNR), and parent-vessel contact angle (PV-CA)) to effects on the hemodynamic responses (aneurysmal and neck-plane root-mean-square velocity magnitude (Vrms), aneurysmal wall shear stress (WSS), and cross-neck flow (CNF)). Two anatomical aneurysm models were also examined to investigate how well the idealized findings would translate to more realistic CA geometries. DNR made the greatest contributions to effects on hemodynamics including a 75.05% contribution to aneurysmal Vrms and greater than 35% contributions to all responses. DS made the next greatest contributions, including a 43.94% contribution to CNF and greater than 20% contributions to all responses. PV-CA and several factor interactions also made contributions of greater than 10%. The anatomical aneurysm models and the most similar idealized templates demonstrated consistent hemodynamic response patterns. This study demonstrates how individual geometric factors, and combinations thereof, influence CA hemodynamics. Bridging the gap between geometry and flow in this quantitative yet practical way may have potential to improve CA evaluation and treatment criteria. Agreement among results from idealized and anatomical models further supports the potential for a template-based approach to play a useful role in clinical practice.

Computational Fluid Dynamics to Evaluate the Management of a Giant Internal Carotid Artery Aneurysm

BACKGROUND

Giant intracranial aneurysms are rare lesions that present uniquely complex therapeutic challenges. Computational fluid dynamics (CFD) has been used to simulate the hemodynamic environments of developing and ruptured cerebral aneurysms. In this study, we use CFD to examine retrospectively hemodynamic changes during the complicated clinical course of a giant carotid aneurysm.

OBJECTIVE

To take an innovative, CFD-based approach to retrospective analysis of the surgical management and clinical course of a giant carotid aneurysm.

METHODS

Pre- and posttreatment image data were first segmented to produce computational aneurysm models. Flow within the models was then simulated using CFD. Simulated flow and wall shear stress (WSS) profiles were analyzed and used to examine hemodynamic changes during the clinical course of the patient, after 2 independent treatments.

RESULTS

Greater WSS magnitudes and a more localized flow impingement region were observed at the distal portion of the aneurysm after both clinical interventions. These relative, acute changes in hemodynamic features at the distal aneurysm wall were greatest after the second intervention and may have preceded rupture of the aneurysm in that region.

CONCLUSIONS

The application of CFD to the management of a giant intracranial aneurysm showed unexpected posttreatment changes in flow and WSS profiles. The simulation results offer a viable explanation for the observed clinical course. This study demonstrates potential for the use of CFD preoperatively for decision-making in the surgical and endovascular management of intracranial aneurysms.

Abstract WP76: Investigation of the Influence of Coil Configuration on Cerebral Aneurysm Fluid Dynamics Using a Novel Finite Element Approach

INTRODUCTION: Despite more than a decade of endovascular coil treatment, the effects of coils on cerebral aneurysm (CA) hemodynamics are still poorly understood. Coils present several challenges to in vivo and in vitro flow measurement techniques and previous in silico methods have suffered from large assumptions on coil geometry. Here we present the first fluid dynamic simulations of coiled CAs that consider the structure and deployment mechanics of embolic coils. We also investigate the influence of coil packing density, design, and configuration on CA fluid dynamics.

Methods: Coil deployment was modeled using a novel finite element approach that realistically simulates coil dynamics during deployment. Two coil designs were investigated: helical and 3D. Coil design and material properties were matched to manufacturer specifications. Five deployment sequences of each coil design, at different microcatheter placements, were simulated in two idealized CA models with variable neck sizes. Blood flow was simulated using computational fluid dynamics. Simulated deployments and fluid dynamics were then compared to deployments of actual coils in identical physical CA models and in vitro particle image velocimetry flow measurements.

Results: Simulated results closely matched in vitro data. Reductions in aneurysmal velocity magnitudes were largest for 3D coils and in a narrow-neck model. In that model, 3D coil deployments reduced average aneurysmal velocity magnitudes by a 51% - 69% range at packing densities less than 20% and by a 74% - 84% range at packing densities greater than 30%. Linear regression results showed reductions were strongly dependent on the spacing between coil loops within the aneurysm and packing density, with correlations of 0.6 and 0.7 respectively.

Conclusion: Coil design and packing density may play equally important roles in determining CA hemodynamics. Results in an anatomical model will also be presented. The proposed virtual coiling approach represents a novel and effective method for realistically simulating coiled CAs, and is an important step towards clinical preoperative planning of coil treatment.

Abstract 178: In-vitro Fluid Dynamic Investigation of a Novel Hyper Elastic-Thin Film Nitinol Stent and the Pipeline Embolization Device for Cerebral Aneurysm Treatment

Introduction: Fusiform and wide-neck intracranial aneurysms (ICAs) can be challenging to treat with conventional endovascular or surgical means. Recently developed low porosity stents, such as the pipeline embolization device (PED), are designed to treat these ICAs by diverting flow away from the aneurysmal sac. However, low porosity stents rely on a dense metal mesh to divert flow, which reduces flexibility and increases the risk of perforator blockage. In this study, we compare fluid dynamic performance between the PED and a novel high porosity stent fabricated from Hyper Elastic-Thin Film Nitinol (HE-TFN).

Methods: An idealized model of a sidewall ICA with a collateral branch, located immediately upstream of the aneurysm, was constructed from transparent silicone. A blood analog solution was circulated through the model at steady and pulsatile flow rates spanning a range of physiologic conditions. The PED and two HE-TFN stents, with pore densities of 8 and 21 pores/mm 2 for 500 and 300 υm pore meshes respectively, were deployed into the model. Each stent was placed across the aneurysm and collateral. Volumetric flow velocity data were acquired before and after stent placement using particle image velocimetry. Computational fluid dynamic (CFD) simulations were also conducted.

Results: For both steady and pulsatile conditions, the 300 HE-TFN stent led to the largest drops in RMS Velocity Magnitude in the aneurysmal sac and in cross-neck flow. Under pulsatile conditions, the average drops in aneurysmal RMS Velocity Magnitude over the cardiac cycle, for the range of parent-vessel flow rates investigated, were 42.8-73.7% for the PED, 46.4-58.1% for the 500 HE-TFN, and 68.9-82.7% for the 300 HE-TFN. The largest drops were observed at lower parent-vessel flow rates and at peak systole. Examination of collateral flows showed that the PED led to the largest drops in collateral RMS Velocity Magnitude. Under pulsatile conditions, the average drops in collateral RMS Velocity Magnitude over the cardiac cycle were 38.3-46.1% for the PED, 14.0-25.9% for the 500 HE-TFN, and 34.5-40.8% for the 300 HE-TFN. For steady flow, both the aneurysmal and collateral performance metrics followed similar trends.

Conclusion: The 300 HE-TFN stent led to larger reductions in cross-neck flow than the PED. This may be due to the higher pore density of the HE-TFN, which may be of greater importance for aneurysm occlusion than absolute porosity. Additionally, the ultra low profile, thin struts of the HE-TFN reduce perforator blockage as demonstrated by increased post-treatment collateral flows as compared to the PED. Overall, the 300 HE-TFN device performed best among the flow diversion devices examined by this study. CFD results characterizing the flow dynamics of each device will also be presented.

Insecticide treated curtains and allelic polymorphism of Plasmodium falciparum genes in a rural area of Burkina Faso (west Africa)

To assess the possible impact of insecticide treated curtains (ITC) on the composition of a Plasmodium falciparum population in a rural area of Burkina Faso, blood samples were collected during the rainy season of 1997 from 226 children aged 3-6 years, from 4 villages equipped with ITC and 2 control villages without ITC. The analysis of fragment lengths of 3 highly polymorphic P. falciparum genes (msp-1, msp-2 and glurp) revealed a maximum number of 3 alleles per infected person for each gene. The mean number of clones per infected person was similar in villages with and without ITC.

Genotyping of Plasmodium falciparum gametocytes by reverse transcriptase polymerase chain reaction

A molecular assay has been developed for the specific detection and genetic characterisation of Plasmodium falciparum gametocytes in the blood of malaria infected individuals. The assay is based on the reverse transcription and polymerase chain reaction (RT-PCR) amplification of the messenger RNA of gene pfg377, a sexual-stage specific transcript abundantly produced in maturing gametocytes. The gene contains four regions of repetitive sequences, of which region 3 was shown to be the most polymorphic in laboratory clones and field isolates of the parasite. Analysis of samples of malaria infected blood by RT-PCR specific for region 3 has enabled identification of multiple gametocyte-producing clones within single infections. The assay is able to detect gametocytes below the threshold of microscopic detection, and is highly specific for its gametocyte targets also in the presence of a vast excess of asexual forms.

Seasonal variation in agglutination of Plasmodium falciparum-infected erythrocytes

Agglutination and rosette formation are in vitro characteristics of Plasmodium falciparum-infected erythrocytes, which have been associated with host protective immune responses and also with parasite virulence. The present study was carried out in an area of seasonal and unstable malaria transmission in eastern Sudan. Plasma samples were obtained before, during, and after the transmission season from a volunteer cohort of 64 individuals seven years of age and older. These plasmas were assayed for their ability to agglutinate cultured parasitized erythrocytes originally obtained from acute malaria infection samples taken from five of the cohort members. Our data show that the capacity of donor plasma samples to agglutinate parasitized cells depended largely on the time of sampling relative to the transmission season, at least within this epidemiologic setting. Thus, although less than half of the pretransmission season samples could agglutinate any of the five lines of cultured parasites, all post-transmission season samples could agglutinate at least one of the parasite lines, with 74% agglutinating two or more lines. This increase in the agglutination capacity of individual plasma samples after the transmission season occurred essentially regardless of whether an individual had experienced a clinical malaria attack during the transmission season. The study thus confirms the acquisition of agglutinating antibodies following episodes of clinical malaria, but also demonstrates that such acquisition can take place in the absence of disease, presumably as a consequence of subclinical infection. This is the first demonstration of marked seasonal fluctuations in the capacity of individuals' sera to agglutinate parasitized red blood cells. Possible explanations for this effect include a decrease in the levels of agglutinating antibodies between seasons, or shifts in the antigens being recognized by such antibodies from one transmission season to the next. Finally, we showed the existence of marked seasonal fluctuation in the levels of agglutinating antibodies, either because levels of such antibodies are not sustained between seasons or because the antigens recognized change from one season to the next.

Detection of very low level Plasmodium falciparum infections using the nested polymerase chain reaction and a reassessment of the epidemiology of unstable malaria in Sudan

We have used the nested polymerase chain reaction (PCR) to assay for low level Plasmodium falciparum infections that were below the threshold of detection of blood film examination. This revealed a substantial group of asymptomatic, submicroscopically patent infections within the population of a Sudanese village present throughout the year although clinical malaria episodes were almost entirely confined to the transmission season. In our September, January, April, and June surveys, the PCR-detected prevalences were 13%, 19%, 24%, and 19%, respectively. These figures reveal a much higher prevalence of dry season infection than previous microscopic surveys have indicated. Furthermore, 20% of a cohort of 79 individuals were healthy throughout the September to November transmission season but were PCR-positive for P. falciparum in a least one of a series of samples taken in the ensuing months. Levels of exposure to P. falciparum infection were therefore higher than was previously believed in this region, highlighting the fact that many individuals were infected but healthy for most of the year. The reservoir parasite population was thus larger and more stable than previously thought, a finding that is consistent with the high levels of genetic variation at polymorphic loci reported from analysis of P. falciparum parasites in this area.

Genetic evidence that RI chloroquine resistance of Plasmodium falciparum is caused by recrudescence of resistant parasites

Isolates of Plasmodium falciparum from patients in a Sudanese village exhibiting RI resistance to chloroquine have been typed for allelic variants of 2 merozoite surface antigens, MSP1 and MSP2. Blood forms were taken from each patient before chloroquine was administered, and after parasites had reappeared following treatment. Each patient was found to be infected with genetically different parasites. However, in each patient the parasites of the recrudescent infections possessed the same alleles of each gene as those of the primary infection. The results show that the parasites which reappeared after chloroquine were a genuine recrudescence of the primary forms, and not derived from a new infection.