NPL's new absorbed dose standard for the calibration of HDR 192Ir brachytherapy sources

Abstract

A novel graphite calorimeter for absorbed dose rate measurements close to high dose rate (HDR) 192Ir brachytherapy sources has been designed and built at the UK National Physical Laboratory (NPL). The graphite calorimeter allows a more direct calibration of HDR 192Ir sources in terms of absorbed dose rate to water at a distance of 1 cm, , compared with the current air kerma-based calibration method, where is determined as the product of the measured air kerma strength and the dose rate constant, Λ, resulting in overall standard uncertainties of up to 5%. With the new absorbed dose standard, can be measured directly with standard uncertainties between 0.7% and 1.0%, depending on the operating mode of the calorimeter. A Nucletron microSelectron-v1 Classic HDR 192Ir source was calibrated with the calorimeter in terms of . The same source was also calibrated with NPL's HDR 192Ir air kerma primary standard in terms of reference air kerma rate. Combining both measurements yielded the experimentally determined dose rate constant of the 192Ir source.