Dr Daric Erminote

Mar 11, 2021

15 min read

Impact Evaluation Method to dose element and source type in Nuclear Medicine fields

Abstract: For a realistic 18F simulation of dosimetry purposes, the preconfigured ‘Fluor18’ source, which simulates the positrons emission spectrum, should be used with all physical process of radiation interaction with matter. In conclusion, GATE application is a reliable and friendly environment for dose estimation in nuclear medicine imaging. GATE application (Geant4 Application for Emission Tomography) provides a series of tools that allow the collection of data from the interaction of radiation with matter during simulation, such as energy deposited and particles created within a volume, among others. The objective of this work is to evaluate the impact of the dose element size on the simulation of the absorbed dose in an attenuating medium in GATE application, using 99mTc and 18F point sources. The influence of the dose map elements (dosel) size was investigated on the absorbed dose, as well as the impact of different source configurations. The results show that a matrix with larger voxels underestimates the absorbed dose values, especially when closer to the source. Thus, for a more accurate dosimetry it is recommended to use smaller dosels near the source. In relation to 18F simulation, they must be performed with the source preset as ‘Fluor18’, so all physical processes can be properly considered. It is concluded that the GATE application is a reliable environment for dose estimation in nuclear medicine imaging, allowing the investigation and selection of the most relevant radiation interaction processes with the material to perform internal dosimetry.

1. Introduction

GATE (Geant4 Application for Emission Tomography) is a toolkit for the application of Geant4 for Monte Carlo simulation (MC) for emission tomography. It is an open source simulation platform in MC, which incorporates the Geant4 libraries, in a modular, versatile tool package programmable through scripts, for simulating medical images, radiotherapy and dosimetry in the same environment1–3.

2. Materials and Methods

Figure 1. Modeled geometry. In cyan color, the simulation world box. In red, the 15 cm radius sphere with water, in which the dose is determined. In the center of the sphere, in yellow, is the point source.
Figure 2. 2D representation of the concentric spheres around a centered radioactive source, in which the dose absorbed by the DPK5 method is calculated.

3. Resultados

Figure 3. Absorbed dose normalized to the maximum dose value, for the 99mTc source, depending on the distance from the source, for different dosage sizes.
Figure 5. Doses absorbed in different doses for the 18F source, depending on the distance from the source. In (a) the absolute doses are presented for each canopy size. In (b), the normalized dose. The y-axis is on a logarithmic scale.
Figure 8. Dose absorbed due to all processes (black line) for the “Fluor18” source. In green, energy deposition process without ionization of the medium and only with Compton scattering (EC) enabled.

4. Discussion

5. Conclusions

6. References