LNE-LNHB air-kerma and absorbed dose to water primary standards for low dose-rate 125I brachytherapy sources

The devices and methods applied for the LNE-LNHB primary standards in terms of reference air-kerma and absorbed dose to water for low dose-rate brachytherapy sources are described. Both standards are based on ionimetric measurements, using a circular-shaped free-in-air ionization chamber, and Monte Carlo calculated conversion factors. Results for an IBt Bebig 125I source are presented and used here to assess the dose-rate constant. Uncertainties of 1.5% and 1.6% (with k = 1) were found for the air-kerma rate and the absorbed dose to water rate estimated with the new primary standards. Good agreement was found between our values and the AAPM published dose-rate constants. Comparisons with other primary standards are in progress. (authors)