Treatment strategies and clinical outcomes in consecutive patients with locally advanced pancreatic cancer:A multicenter prospective cohort

Introduction: Since current studies on locally advanced pancreatic cancer (LAPC) mainly report from single, high-volume centers, it is unclear if outcomes can be translated to daily clinical practice. This study provides treatment strategies and clinical outcomes within a multicenter cohort of unselected patients with LAPC. Materials and methods: Consecutive patients with LAPC according to Dutch Pancreatic Cancer Group criteria, were prospectively included in 14 centers from April 2015 until December 2017. A centralized expert panel reviewed response according to RECIST v1.1 and potential surgical resectability. Primary outcome was median overall survival (mOS), stratified for primary treatment strategy. Results: Overall, 422 patients were included, of whom 77% (n = 326) received chemotherapy. The majority started with FOLFIRINOX (77%, 252/326) with a median of six cycles (IQR 4-10). Gemcitabine monotherapy was given to 13% (41/326) of patients and nab-paclitaxel/gemcitabine to 10% (33/326), with a median of two (IQR 3-5) and three (IQR 3-5) cycles respectively. The mOS of the entire cohort was 10 months (95%CI 9-11). In patients treated with FOLFIRINOX, gemcitabine monotherapy, or nab-paclitaxel/gemcitabine, mOS was 14 (95%CI 13-15), 9 (95%CI 8-10), and 9 months (95%CI 8-10), respectively. A resection was performed in 13% (32/252) of patients after FOLFIRINOX, resulting in a mOS of 23 months (95%CI 12-34). Conclusion: This multicenter unselected cohort of patients with LAPC resulted in a 14 month mOS and a 13% resection rate after FOLFIRINOX. These data put previous results in perspective, enable us to inform patients with more accurate survival numbers and will support decision-making in clinical practice. (C) 2020 The Authors. Published by Elsevier Ltd

A novel shape optimization approach for strained gridshells: Design and construction of a simply supported gridshell

© 2019 Elsevier Ltd Strained gridshells are reticulated shell structures that are erected from a flat grid of initially straight laths. The structural efficiency of a gridshell is determined by its shape, which is traditionally designed using form-finding techniques. However, these techniques are primarily used to generate structures in pure tension or compression for a single load case only. In cases where classic form-finding techniques are not applicable, such as for cantilevering gridshells or simply supported gridshells, numerical optimization can be used to find a suitable shape. In this paper, an optimization procedure is proposed that optimizes the shape of a strained gridshell for a given grid. The forces applied to erect the gridshell are chosen as the design variables. These erection forces are optimized to minimize the so-called end-compliance, which is defined as the inner product of the external loads and the resulting displacements. The method of moving asymptotes is adopted to solve the optimization problem and implicit dynamic relaxation is used to solve the nonlinear equilibrium equations. Geometric nonlinearity is taken into account by using co-rotational beam elements to model the gridshell laths. To validate the proposed approach, a 6×6 m 2 prototype was built. The results show that this approach allows the structure to be optimized considering multiple load cases, while accounting for practical building constraints, and potential designer constraints.status: publishe

On the equivalence of dynamic relaxation and the Newton-Raphson method

Copyright © 2017 John Wiley & Sons, Ltd. Dynamic relaxation is an iterative method to solve nonlinear systems of equations, which is frequently used for form finding and analysis of structures that undergo large displacements. It is based on the solution of a fictitious dynamic problem where the vibrations of the structure are traced by means of a time integration scheme until a static equilibrium is reached. Fictitious values are used for the mass and damping parameters. Heuristic rules exist to determine these values in such a way that the time integration procedure converges rapidly without becoming unstable. Central to these heuristic rules is the assumption that the highest convergence rate is achieved when the ratio of the highest and lowest eigenfrequency of the structure is minimal. This short communication shows that all eigenfrequencies become identical when a fictitious mass matrix proportional to the stiffness matrix is used. If, in addition, specific values are used for the fictitious damping parameters and the time integration step, the dynamic relaxation method becomes completely equivalent to the Newton-Raphson method. The Newton-Raphson method can therefore be regarded as a specific form of dynamic relaxation. This insight may help to interpret and improve nonlinear solvers based on dynamic relaxation and/or the Newton-Raphson method.status: publishe

On the equivalence of dynamic relaxation and the Newton-Raphson method: application to the design and analysis of bending-active structures

Dynamic relaxation is a form-finding and analysis method that has proven its effectiveness in the context of tension/compression structures such as cable nets, membranes and tensegrity structures. Recently, however, an increasing interest in bending-active structures has stimulated researchers to include the effects of bending and torsion in the dynamic relaxation process, using either Three-Degree-of-Freedom (3-DoF) beam elements (Barnes et al. [4]), or 4-DoF beam elements (Du Peloux et al. [12], D’Amico et al. [10]), or 6-DoF beam elements (Li and Knippers [13]). The stability and convergence speed of the dynamic relaxation solver depends on the choice of the fictitious masses for all degrees of freedom. Although 6-DoF beam elements are in principle preferred over 3-DoF and 4-DoF beam elements because of their higher accuracy (D’Amico et al. [10]), their use in dynamic relaxation is hindered by the fact that no heuristic rules are available for the choice of the fictitious masses. In this paper the numerical stability of the dynamic relaxation solver is investigated for 6-DoF beam elements using modal analysis. A fictitious mass matrix proportional to the stiffness matrix is put forward as the most suitable choice considering numerical stability and convergence, as it causes all eigenfrequencies of the structure to coincide. Moreover, it is shown that for this choice of mass matrix and a specific choice for the damping ratio and the time step, the dynamic relaxation method becomes identical to the Newton-Raphson method, which is well known for its fast convergence. For numerically challenging problems, the stability of the classic Newton-Raphson method can be improved by increasing the damping ratio and/or decreasing the time step. We applied the proposed approach to three test cases involving bending-active structures in order to verify its accuracy and convergence speed. The results show that the dynamic relaxation routine indeed converges in a very small number of iterations, while still maintaining the accuracy of 6-DoF beam elements. The combination of high accuracy and low computation time makes this approach well-suited for both the form finding and the analysis of spatial structures undergoing large displacements.no ISBN/ISSNstatus: publishe

A fast and accurate dynamic relaxation approach for form-finding and analysis of bending-active structures

status: publishe