Monte Carlo determination of dosimetry parameters for model 6711 125I seed

Objective To calculate the brachytherapy dosimetry parameters for Model 6711 125I seeds.Methods Brachytherapy dosimetry parameters are determined in accordance with the AAPM Task Group No.43 TG43-U1 dosimetry protocol.The anisotropy funetion,radial dose function,dose rate constant and dose distributions in different medium are calculated using EGSnrc code with the updated XCOM cross section libraries.Results The anisotropy function and the radial dose function are in good agreement with the data reported lately.The calculated dose rate constant is 0.951 cGy·h-1·U-1,in a 1.45% agreement with the consensus data recommended by AAPM TG43-U1 report.Conclusions The dose field around the seed source shows the characteristics of very low dose rate and very high dose gradient.A small structure iS found in the small polar angle range and the small distances of the anisotropy function. Key words: 125I seed;  Monte Carlo calculation;  Anisotropy function; Radial dose function; Dose rate constant; Dose distribution