Imprimir Resumo


Teste
Abstract: 139-1

139-1

Analysis of TG-43 dosimetric parameters for Ir-192 HDR brachytherapy source using computational simulation with Monte Carlo method

Authors:
Alice Sant Anna Albuquerque (IRD - Instituto de Radioproteção e Dosimetria) ; Denison de Souza Santos (IRD - Instituto de Radioproteção e Dosimetria) ; Luiz Antonio Ribeiro da Rosa (IRD - Instituto de Radioproteção e Dosimetria)

Abstract:

According to the World Health Organization, cancer is among the leading causes of death worldwide before the age of 70[1]. In Brazil, the estimated number of new cases for the 2023-2025 triennium is 704,000[2]. Currently, radiotherapy is recommended as part of the treatment for approximately 70% of patients undergoing some form of cancer therapy [3]. Brachytherapy procedures for the treatment of prostate cancer, head and neck cancers, lung cancer, and sarcomas can be either permanent or temporary [5], involving the insertion of catheters to introduce a radioactive source, typically HDR Ir-192 or, less commonly, Co-60. The Task Group 43 recommends a formalism for calculating dose quantities in water phantoms, defining various dosimetric quantities such as the radial dose function, dose rate constant, and anisotropy function to calculate therapeutic doses for tumors and surrounding tissues with dose constraints to avoid serious damage from the treatment [6]. The objective of this study is to evaluate the Ir-192 Buchler G089 source, manufactured by Amersham, through TG-43 formalism using Monte Carlo simulation.
Methodology
The brachytherapy source used in this study was the Buchler developed by Amersham. Its geometry consists of a solid Ir-192 core with a diameter of 1mm and a length of 1.3mm encapsulated in a stainless steel shield. The end of the shield is a hemisphere with a diameter of 1.6mm, offset from the center of the source by 0.95mm. The cavity containing the Ir-192 source is a hollow cylinder with a length of 1.4mm and inner and outer diameters of 1.2mm and 1.6mm, respectively. Next to the cavity, there is a solid cylindrical section with a length of 1.76mm and a diameter of 1.6mm, followed by a hollow cylinder with a length of 1.34mm and inner and outer diameters of 1.1mm and 1.6mm, respectively. Inserted into this hollow section is a 6cm long stainless steel wire. The active length of this source is 1.3mm.
To evaluate the source, we used the mathematical formalism proposed in TG-43, which recommends a formalism for calculating dose quantities in water phantoms by defining different dosimetric quantities such as the radial dose function, dose rate constant, and anisotropy function to calculate therapeutic doses for tumors and surrounding tissues that have dose constraints to avoid serious treatment effects.
For this work, we used the radial dose function as the parameter for validating the source. 
To evaluate the Buchler source, its modeling was implemented in Geant4. The dose was then simulated for 36 different radial ranging from 0.2cm to 20cm using a number of histories of 10⁸. The radial dose function was then obtained from the dose and compared to that obtained by Taylor et al.[7].
Results and Discussion
The simulation results show good agreement with the data from Taylor et al., especially for radial distances close to the source. As the radial distance increases, a slight divergence between the simulated values and the reference data is observed. However, the values remain within an acceptable error range
Conclusion
The simulation results show good agreement with the data from Taylor et al., especially for radial distances close to the source. As the radial distance increases, a slight divergence between the simulated values and the reference data is observed. However, the values remain within an acceptable error range.

Keywords:
 brachytherapy, TG-43, Geant4