Monte Carlo-aided dosimetry of the new Bebig IsoSeed® ¹⁰³Pd interstitial brachytherapy seed

A new model ¹⁰³Pd interstitial brachytherapy source, the IsoSeed® ¹⁰³Pd, was recently introduced by Bebig Isotopentechnik und Umweltdiagnostik GmbH for permanent implant applications. This study presents the first quantitative theoretical study of the seed's dosimetric quantities. Monte Carlo photon transport (MCPT) simulation techniques have been used to evaluate the dose-rate distributions around the model IsoSeed® ¹⁰³Pd source in liquid water and air phantoms. These results have been used to calculate and tabulate the anisotropy function, F(r, θ), radial dose function, g(r), and anisotropy factors, φ(r), and dose-rate constant as defined by AAPM Task Group 43 (TG-43) Report. Cartesian "away" and "along" tables, giving the dose rates per unit air-kerma strength in water in the range 0.1-3 cm distance around the seed have also been tabulated. The dose-rate constant, A, was evaluated by simulating the wide-angle, free-air chamber (WAFAC) calibration geometry recently implemented by NIST (National Institute of Standards and Technology) to realize the primary standard of air-kerma strength (S_K,N99) for low-energy photon-emitting brachytherapy sources. The dose-rate constant has been found to be Λ=0.660±0.017 in units of dose-rate per unit air-kerma strength (cGy·h^-1·U^-1).