Dosimetric Parameters Estimation for I-125 (Model 6711) Brachytherapy Source

Determination of dose distribution around the applied sources in brachytherapy especially with low-energy is crucial during establishment of treatment planning. In this study dosimetric parameters of a model 6711 I-125 brachytherapy source were calculated using Monte Carlo simulation method. Subject and A homogeneity water phantom with 30 cm3 dimensions was simulated with MCNPX (2. 6. 0) code. A model 6711 I-125 brachytherapy source with considering of its details (materials، dimensions and its emitted spectrum) was located in the center of phantom. Air Kerma strength، Sk، of source was calculated with locating source inside the vacuum sphere. Recommended dosimetric parameters by AAPM، TG-43 protocol were calculated for the model 6711 I-125 brachytherapy source in this phantom. The air kerma strength of the model 6711 I-125 source was estimated as equal to 0. 557 cGycm2h-1mCi-1. Dose rate constant was 0. 885 cGyh-1U-1. The Radial dose function with 5 degree equation and with regression of 0. 9989 was estimated by g (r) = -. 0001r4+0. 0026 r3-0. 0178 r2-0. 0970 r+1. 0995. The 5 degree equations for the anisotropy dose functions were calculated with R2>0. 99. In spite of low-energy emission photons and high dose gradients with radial distance، dosimetric parameters of the model 6711 I-125 source can be calculated by MCNPX Monte Carlo code with acceptable accuracy. Calculated parameters for the model 6711 I-125 brachytherapy source can be used for treatment planning systems in brachytherapy.