A tool for precise calculation of organ doses in voxelised geometries using GAMOS/Geant4 with a graphical user interface

Introduction: The limit of the method of calculating organ doses using voxelised phantoms with a Monte Carlo simulation code is that dose calculation errors in the boundaries of the organs are especially relevant for thin, small or complex geometries. In this report, we describe a tool that helps overcome this problem, accurately calculating organ doses by applying the “parallel geometry” utility feature of Geant4 through the GAMOS framework. Methods and methods: We have tried to simplify the use of this tool by automatically processing the different DICOM image modalities (CT, PT, ST, NM), and by including the automatic conversion of the structures found in a DICOM RTSTRUCT file into Geant4 volumes that build the parallel geometry. For Nuclear Medicine applications, the DICOM PT, ST or NM images are converted into probabilities of generation of primary particles in each voxel, and the DICOM CT images into materials and material densities. For radiotherapy treatments, the DICOM RTPlan or RTIonPlan may also be used, hence the user only needs to describe the accelerator geometry. We also provide a Graphical User Interface for ease of use by for inexperienced users in Monte Carlo. Results: We have tested the functionality of the tool with an I-131 thyroid cancer treatment, and obtained the expected energy deposition and dose differences, given that the particle source, geometry and structures are defined. Conclusions: In summary, we provide an easy-to-use tool to calculate, with high accuracy, organ doses, taking into account their exact geometry as painted by the medical personnel on a voxelised phantom.

ADDING TWO NEW CONTACT CIRCUMSTANCES TO ‘MERGED PHANTOM TOOL’ AND A TECHNIQUE TO CONVERT STRUCTURE INFORMATION SEGMENTED BY THE CARIMAS SOFTWARE INTO GEANT4 GEOMETRY

Two new contact circumstances called ‘stand-lie’ and ‘front–rear’ are implemented to the merged phantom tool. To allow more flexibility for users when they calculate the dose for a volume of interest (VOI) with arbitrary geometry, an optional utility to convert segmented structure information from the CARIMAS software into parallel geometry of GEANT4 is provided. The effective dose for a person who has been in contact with a male patient being treated for thyroid cancer with 131I is calculated for four circumstances: opposite, side by side, stand-lie and front–rear. The biggest dose is the ‘opposite’ circumstance and the smallest one is the ‘stand-lie’ circumstance. Using the dose distribution in the patient’s body and applying the right circumstance should be done to optimise the dose calculation for the contact person.

Metodología numérica para resolver ecuaciones del modelo elíptico de un superconductor tipo II anisótropo

Based on the macroscopic description of a type II anisotropic superconducting material, this paper presents numerical methods to model the magnetic induction of these materials in a critical state. In this case, an elliptical model of the critical state is used to describe a type II anisotropic superconductor in terms of parallel geometry. It describes how the mathematical problem is solved in order to find the distribution of magnetic induction in the material. This consists of solving a system of ordinary differential equations. In order to do this, the standard libraries of MATLAB software were used. Two routines were especially used, the first of which gives an initial rough result which is then refined with the second routine. The authors have ample experience in the macroscopic study of the magnetic properties of type II superconductors as well as international publications in this specialized study area.