Calorimetric Determination of Absorbed Dose to Water for an ~192Ir HDR Brachytherapy Source in Near-Field Geometry

摘要

~192Ir brachytherapy sources have been calibrated in terms of the reference air kerma rate at the Physikalisch-Technische Bundesanstalt (PTB) for more than 15 years. To reduce the uncertainty of the conversion factor from the reference air kerma rate to the absorbed dose to water at a distance of 1 cm from the source, the PTB has started a new project for the direct determination of the absorbed dose to water at a short distance from a clinical l92Ir HDR (high dose rate) source by use of a water calorimeter. The experimental set-up, heat transfer calculations and calorimetric measurements in three different depths in water are presented. For the determination of the dose rate constant A, additional measurements of the reference air kerma rate were performed and the radial dose function was determined by means of a plastic scintillation detector system as well as by Monte Carlo calculations.