Monte Carlo simulation study of dosimetric parameters of Varian HDR ¹⁹²Ir source

Objective: To study the dosimetric parameters of Varian GammaMed Plus HDR ¹⁹²Ir source via Monte Carlo (MC) method based on the recommendation of the American Association of Physicist in Medicine (AAPM) and European Society for Radiotherapy and Oncology (ESTRO). Methods: Using the Monte Carlo program EGSnrc, an accurate model of ¹⁹²Ir source for MC calculations was establish firstly. Through formula derivation, bilinear interpolation and unit conversion, the air kerma strength per unit source activity, the dose rate constant, radial dose function and anisotropy function was obtained then, and compare the result with those in other published studies. Results: The air kerma strength per unit source activity was 9.781 × 10^-8 U/Bq. The dose rate constant was 1.113 cGy · h^-1 · U^-1, with a discrepancy of less than 0.4% compared with result published in other works. Furthermore, the curves of radial dose function and anisotropy function overall agree with the data shown in the literature. Conclusions: The feasibility of performing dosimetric studies of ¹⁹²Ir source using the MC software EGSnrc was demonstrated. This work provides a theoretical guidance on analysis of the dose distribution of brachytherapy and on evaluation of the dose accuracy of clinical radiotherapy. (authors)