Monte Carlo calculations of dosimetry parameters of the urocor prostaseed 125I source

This report presents the results of Monte Carlo calculations of the dosimetric parameters of the Urocor ProstaSeed 1251 seed source. This source contains five spherical silver markers, of 0.5 mm diameter, with 1251 deposited on the spheres through ion exchange. The silver spheres are then encapsulated within a 0.8 mm in diameter and 4.5 mm long cylindrical shell of titanium, as is common to this type of sources. Physical dimensions of the source are confirmed by measurement. Four (4) geometric models of the source, based on different assumptions on the locations of the silver spheres within the seed, were used in dose rate calculations. Monte Carlo photon transport simulation was used to calculate the dosimetric parameters of dose rate constant, radial dose function, and anisotropy function using these geometric models of the source. The Monte Carlo calculated dose rate constant of the ProstaSeed source was found equal to 0.925 cGy/Uh with approximate uncertainties of 5%. Radial dose function values and anisotropy function values were derived from the relative dose distribution around the source calculated by the Monte Carlo code. The calculated values of these dosimetric parameters agree with previously published thermoluminescence-dosimeter-measured values for this source after consideration of measurement and calculation uncertainties.