Open AccessMonte Carlo study of TG‐43 dosimetry parameters of GammaMed Plus high dose rate 192 Ir brachytherapy source using TOPAS
Author(s) -
Wu Jianan,
Xie Yaoqin,
Ding Zhen,
Li Feipeng,
Wang Luhua
Publication year - 2021
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.13252
Subject(s) - kerma , monte carlo method , brachytherapy , dosimetry , physics , nuclear medicine , dose rate , computational physics , anisotropy , optics , mathematics , medical physics , medicine , radiation therapy , statistics
Purpose To develop a simulation model for GammaMed Plus high dose rate 192 Ir brachytherapy source in TOPAS Monte Carlo software and validate it by calculating the TG‐43 dosimetry parameters and comparing them with published data. Methods We built a model for GammaMed Plus high dose rate brachytherapy source in TOPAS. The TG‐43 dosimetry parameters including air‐kerma strength S K , dose‐rate constant Λ , radial dose function g L ( r ), and 2D anisotropy function F ( r , θ ) were calculated using Monte Carlo simulation with Geant4 physics models and NNDC 192 Ir spectrum. Calculations using an old 192 Ir spectrum were also carried out to evaluate the impact of incident spectrum and cross sections. The results were compared with published data. Results For calculations using the NNDC spectrum, the air‐kerma strength per unit source activity S K / A and Λ were 1.0139 × 10 ‐7 U/Bq and 1.1101 cGy.h −1 .U −1 , which were 3.56% higher and 0.62% lower than the reference values, respectively. The g L ( r ) agreed with reference values within 1% for radial distances from 2 mm to 20 cm. For radial distances of 1, 3, 5, and 10 cm, the agreements between F ( r , θ ) from this work and the reference data were within 1.5% for 15° < θ < 165°, and within 4% for all θ values. The discrepancies were attributed to the updated source spectrum and cross sections. They caused deviations of the S K / A of 2.90% and 0.64%, respectively. As for g L ( r ), they caused average deviations of −0.22% and 0.48%, respectively. Their impact on F ( r , θ ) was not quantified for the relatively high statistical uncertainties, but basically they did not result in significant discrepancies. Conclusion A model for GammaMed Plus high dose rate 192 Ir brachytherapy source was developed in TOPAS and validated following TG‐43 protocols, which can be used for future studies. The impact of updated incident spectrum and cross sections on the dosimetry parameters was quantified.