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.