Monte Carlo Simulation of Dose Calculation Parameter of Radioactive 125I Brachytherapy Source

The end of silver rod of the domestic ¹²⁵I brachytherapy source is right angle type, which is slightly different from the typical model of 6711 ¹²⁵I brachytherapy source. And it can have influence on the dose calculation parameters. Based on the structure of domestic ¹²⁵I brachytherapy source, dose calculation parameters which are recommended by AAPM TG43-U1 were calculated by Monte Carlo method. The influence of the end of silver rod on the dose calculation parameters was studied. The simulation result of dose rate constant is 0.955 cGy·h-1·U-1 when the air kerma strength was calculated by the point detector, and the difference with the result of the TG43-U1 is within 1.03%. The radial dose function g(r) in the range of 0.05-10 cm at the transverse axis was calculated precisely. Then empiric equation was acquired by curve fitting. 2D anisotropy function F(r,θ) was calculated in 0°-90° and 0.25-7 cm. The source of the right angle structure of the end of the silver rod would cause a hump area of 2D anisotropy function when r equals 0.25 cm.