Dosimetric parameters for three low-energy brachytherapy sources using the Monte Carlo N-particle code.

Monte Carlo calculations have been performed for the purpose of characterizing the dosimetric properties of three brachytherapy sources. The three sources are manufactured by Syncor Pharmaceuticals Inc. and consist of two 125I seeds (BT-125-1 and BT-125-2) and one 103Pd seed (BT-103-3). The BT-125-1 and BT-125-2 seed consists of a solid palladium and silver core, respectively. A thin layer (0.5 microm) of 125I is adsorbed onto the solid core for each seed and encased within a titanium housing. The BT-103-3 seed consists of a central gold marker and four resin balls encased within a titanium housing. A thin layer of 103Pd is bonded onto each resin ball. The dosimetric properties, including the dose rate constant, radial dose function, and anisotropy were calculated in water according to the TG-43 protocol using the Monte Carlo N-Particle code. The dose rate constant was calculated to be 0.955+/-0.005 and 0.967+/-0.005 cGyh(-1) U(-1) for the BT-125-1 and BT- 125-2 seeds, respectively. A dose rate constant of 0.659+/-0.005 cGy h(-1) U(-1) was calculated for the BT-103-3 seed. Radial dose function, g(r), calculated to a distance of 10 cm, and an isotropy function, F(r, theta), calculated for radii from 0.5 to 7.0 cm, were found to be in close agreement with previously published data.