An adaptive spot placement method on Cartesian grid for pencil beam scanning proton therapy

Pencil beam scanning (PBS) proton radiotherapy (RT) offers flexible proton spot placement near treatment targets for delivering tumoricidal radiation dose to tumor targets while sparing organs-at-risk (OAR). Currently the spot placement is mostly based on a non-adaptive sampling (NS) strategy on a Cartesian grid. However, the spot density or spacing during NS is a constant for the Cartesian grid that is independent of the geometry of tumor targets, and thus can be suboptimal in terms of plan quality (e.g., target dose conformality) and delivery efficiency (e.g., number of spots). This work develops an adaptive sampling (AS) spot placement method on the Cartesian grid that fully accounts for the geometry of tumor targets. Compared with NS, AS places (1) a relatively fine grid of spots at the boundary of tumor targets to account for the geometry of tumor targets and treatment uncertainties (setup and range uncertainty) for improving dose conformality, and (2) a relatively coarse grid of spots in the interior of tumor targets to reduce the number of spots for improving delivery efficiency and robustness to the minimum-minitor-unit (MMU) constraint. The results demonstrate that (1) AS achieved comparable plan quality with NS for regular MMU and substantially improved plan quality from NS for large MMU, using merely about 10% of spots from NS, where AS was derived from the same Cartesian grid as NS; (2) on the other hand, with similar number of spots, AS had better plan quality than NS consistently for regular and large MMU.

Design And Numerical Analysis of Morphing Airfoil With Corrugated Geometry In The Application MAV’s

The main objective of the work is to enhance the aerodynamic performance during takeoff and cruise by using newly corrugated airfoil of MAV’s by Morphing it at the trailing edge. In this study, the transient nature of corrugated airfoils at low Reynolds number were assumed to be the flow is laminar, incompressible and two dimensional. The newly corrugated geometry which is parameterized from the camber line using a Radial basis function (RBF) based on interpolation method positioned at the lower surface of the airfoil i.e., NACA0015. Five morphed geometries are designed using ANSYS Space claimer. The computational domain is meshed using cartesian grid, the surface meshes with quadrilateral. Numerical simulations are performed with turbulent models i.e., k-omega, k-epsilon and Spalart allmaras. In the analysis, there is an increment of coefficient of lift and decrease in coefficient of drag by varying Reynolds number. Compared to NACA0015, corrugated NACA0015 shows good results.

A High-Order Finite-Difference Method on Staggered Curvilinear Grids for Seismic Wave Propagation Applications with Topography

ABSTRACT We developed a 3D elastic wave propagation solver that supports topography using staggered curvilinear grids. Our method achieves comparable accuracy to the classical fourth-order staggered grid velocity–stress finite-difference method on a Cartesian grid. We show that the method is provably stable using summation-by-parts operators and weakly imposed boundary conditions via penalty terms. The maximum stable timestep obeys a relationship that depends on the topography-induced grid stretching along the vertical axis. The solutions from the approach are in excellent agreement with verified results for a Gaussian-shaped hill and for a complex topographic model. Compared with a Cartesian grid, the curvilinear grid adds negligible memory requirements, but requires longer simulation times due to smaller timesteps for complex topography. The code shows 94% weak scaling efficiency up to 1014 graphic processing units.