G. Cosmo

Geant4 developments and applications

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Its functionality and modeling capabilities continue to be extended, while its performance is enhanced. An overview of recent developments in diverse areas of the toolkit is presented. These include performance optimization for complex setups; improvements for the propagation in fields; new options for event biasing; and additions and improvements in geometry, physics processes and interactive capabilities

A technique for optimised navigation in regular geometries

The simulation of a DICOM file describing the geometry of a patient through a 3-dimensional grid of several million voxels represents a big challenge in terms of time and memory consumption. We have developed a fast technique to navigate in these regular voxelised geometries in the GEANT4 framework. It takes advantage of the regular structure of the geometry to optimise the location of voxels at tracking time. An option to skip on the fly the voxel boundaries when two contiguous voxels share the same material reduces the number of steps and therefore the simulation time. When the number of materials in the phantom is of the order a few dozens, enough to reach the required precision in medical physics applications, this technique is several times faster than the optimised navigation algorithms implemented in GEANT4, while keeping optimal memory and initialisation time.

Parallel geometries in Geant4: Foundation and recent enhancements

The Geant4 software toolkit simulates the passage of particles through matter. It is utilized in high energy and nuclear physics experiments, in medical physics and space applications.

Optimization of an external beam radiotherapy treatment using GAMOS/Geant4

During the last years the use of Geant4 [1] in medical physics is increasing. Today Geant4 offers the advantage of a well-validated set of physics models, a modern software technology and a big flexibility to tailor it to the user specific application.

Modeling detector geometries in Geant4

The Geometry modeler in Geant4 (a software toolkit for the simulation of the interactions of particles with matter) has been designed to offer to a generic user the ability to describe the geometrical structure of a detector in a very natural way, and allowing an efficient propagation of particles in the geometrical detector model. Advanced techniques for optimizing tracking in the geometrical model have been seriously taken into consideration in the design, both in order to optimize the run-time performance and reduce the physical memory consumption when dealing with complex geometrical setups. The major concepts of geometry modeling in the Geant4 toolkit are here reviewed, with a special focus on the more recent features introduced in the last releases of the software.

Stochastic optimization of GeantV code by use of genetic algorithms

GeantV is a complex system based on the interaction of different modules needed for detector simulation, which include transport of particles in fields, physics models simulating their interactions with matter and a geometrical modeler library for describing the detector and locating the particles and computing the path length to the current volume boundary. The GeantV project is recasting the classical simulation approach to get maximum benefit from SIMD/MIMD computational architectures and highly massive parallel systems. This involves finding the appropriate balance between several aspects influencing computational performance (floating-point performance, usage of off-chip memory bandwidth, specification of cache hierarchy, etc.) and handling a large number of program parameters that have to be optimized to achieve the best simulation throughput. This optimization task can be treated as a black-box optimization problem, which requires searching the optimum set of parameters using only point-wise function evaluations. The goal of this study is to provide a mechanism for optimizing complex systems (high energy physics particle transport simulations) with the help of genetic algorithms and evolution strategies as tuning procedures for massive parallel simulations. One of the described approaches is based on introducing a specific multivariate analysis operator that could be used in case of resource expensive or time consuming evaluations of fitness functions, in order to speed-up the convergence of the black-box optimization problem.

Parallel tally geometry in GEANT4 for medical dose calculation

The use of Monte Carlo calculation is essential in radiation therapy. Monte Carlo simulation is widely used for verifying the dose for nozzle design, quality assurance, and the treatment planning system. GEANT4 simulation toolkit provides many powerful functions suitable for the dose calculation in radiation therapy. In radiation therapy, both a simple homogeneous water phantom and a complex volume extracted from CT data are used for the dose calculation. Therefore, universal access to the particle information regardless to the complexity of the geometries is desirable. We extended functionalities of GEANT4 to allow two independent geometries in one simulation application simultaneously, where one geometry represents real materials and the other represents an artificial geometry for a tally. In this report, we describe the parallel tally geometry in GEANT4 for medical dose calculations. We also report the validation results of this new capability