title: Monte Carlo aided dosimetry of the microselectron pulsed and high dose-rate 192Ir sources.
abstract: Despite the large number of single-stepping source pulsed and high dose-rate (HDR) remote after-loading devices in clinical use, the published literature contain little data characterizing dose-rate distributions around the high-intensity (4 x 10(3)-4 x 10(4) microGy m2h-1) 192Ir sources currently used in these devices. We have used the Monte Carlo method to calculate complete two-dimensional dose-rate distributions about the most widely used high dose-rate source design, as well as the Nucletron pulsed dose-rate (PDR) 192Ir source. A Monte Carlo photon transport code, incorporating the detailed internal geometry of the source, was used to calculate the dose rate per unit air-kerma strength in water medium on the transverse bisecting axis over the 0.15-12 cm distance range. In addition, polar dose profiles were calculated at distances ranging from 0.25 to 5 cm. The PDR and HDR dose-rate distributions are tabulated using the formalism endorsed by the Interstitial Collaborative Working Group and the AAPM Task Group 43, and includes dose-rate constant, radial dose function, anisotropy function, geometry function, and anisotropy factors. The dose-rate constants, lambda, of the MicroSelectron/HDR and PDR sources were found to be 1.115 and 1.128 cGy h-1 per unit air-kerma strength, respectively, in good agreement with previously published data for low dose-rate interstitial 192Ir sources. Oblique filtration by the high-density iridium metal core resulted in deviations from anisotropy as large as 35%-55% near the longitudinal axis of the source. Dose-rate distributions are also presented in Cartesian ("away" and "along") coordinates.
authors.affiliation: Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Williamson
authors.forename: Z
authors.initials: Z
authors.lastname: Li
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D008433:Mathematics; D008961:Models, Structural; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage
chemical_list: D007496:Iridium Radioisotopes