Monte Carlo study of TG‐43 dosimetry parameters of GammaMed Plus high dose rate ¹⁹²Ir brachytherapy source using TOPAS

Abstract

Purpose To develop a simulation model for GammaMed Plus high dose rate 192Ir 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 SK, dose‐rate constant Λ, radial dose function gL(r), and 2D anisotropy function F(r,θ) were calculated using Monte Carlo simulation with Geant4 physics models and NNDC 192Ir spectrum. Calculations using an old 192Ir 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 SK/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 gL(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 SK/A of 2.90% and 0.64%, respectively. As for gL(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 192Ir 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.

Monte Carlo simulation of physical dose enhancement in core-shell magnetic gold nanoparticles with TOPAS

“…In this study, we further evaluated the sensitization properties of the Fe 3 O 4 @AuNP and AuNP under a clinically applied source. We implemented the Varian GammaMed Plus HDR 192 Ir brachytherapy source model (developed by Wu et al using TOPAS (39)) to explore the DEF of the Fe 3 O 4 @AuNP and AuNP irradiated by a brachytherapy source. The particle numbers that were emitted from the brachytherapy source model per keV per initial photon (a total of 10 8 initial photons were used as the source in this simulation), were recorded on a parallel plane at a 2 cm distance from the source center, as presented in Figure 3.…”