Calorimetric Determination of Absorbed Dose to Water for an 192Ir HDR Brachytherapy Source in Near-Field Geometry
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 192Ir 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 ∧, 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.
Keywordsbrachytherapy 192Ir source absorbed dose to water water calorimetry
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