Evaluation of a new brachytherapy iodine-125 source by AAPM TG43 formalism

Dosimetric measurements were performed to characterize a new 125I source that is similar in design to existing sources and that has application in interstitial brachytherapy. Thermoluminescent dosimeters were placed in phantom to measure transverse-axis and angular dose profiles over a range of distances from 0.5 to 7 cm. The data were analyzed in terms of parameters recommended by AAPM Task Group #43. Tabular data evaluated in liquid water are provided for the dose-rate constant, lambda, radial dose function, g(r), the anisotropy function, F(r, theta), the anisotropy factor, phi an(r), the point-source approximation anisotropy constant, phi an, and the point-source average dose rate times the square of distance for unit air kerma strength, r2D(r). The new source is compared to the model 6702 125I source design, demonstrating similar dose-rate constant, lambda, and radial dose function, g(r). Differences in the anisotropy of the dose distributions are discussed. Finally, a comparison of the radial dose distribution is made between liquid water and tissue equivalent materials.