Monte Carlo dosimetry of the 60 Co sources of a new GZP3 HDR afterloading system

Background The purpose of this work was to obtain the dosimetric parameters of the new GZP3 60 Co high-dose-rate afterloading system launched by the Nuclear Power Institute of China, which is comprised of two different 60 Co sources. Methods The Monte Carlo software Geant4 and EGSnrc were employed to derive accurate calculations of the dosimetric parameters of the new GZP3 60 Co brachytherapy source in the range of 0–10 cm, following the formalism proposed by American Association of Physicists in Medicine reports TG43 and TG43U1. Results of the two Monte Carlo codes were compared to verify the accuracy of the data. The source was located in the center of a 30-cm-radius theoretical sphere water phantom. Results For channels 1 and 2 of the new GZP3 60 Co afterloading system, the results of the dose-rate constant (Λ) were 1.115 cGy h −1 U −1 and 1.112 cGy h −1 U −1 , and for channel 3 they were 1.116 cGy h −1 U −1 and 1.113 cGy h −1 U −1 according to the Geant4 and EGSnrc, respectively. The radial dose function in the range of 0.25–10.0 cm in a longitudinal direction was calculated, and the fitting formulas for the function were obtained. The polynomial function for the radial dose function and the anisotropy function (1D and 2D) with a of 0°–175° and an r of 0.5–10.0 cm were obtained. The curves of the radial function and the anisotropy function fitted well compared with the two Monte Carlo software. Conclusion These dosimetric data sets can be used as input data for TPS calculations and quality control for the new GZP3 60 Co afterloading system.