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

摘要

A novel graphite calorimeter for absorbed dose rate measurements close to high dose rate (HDR) ~(192)Ir brachytherapy sources has been designed and built at the UK National Physical Laboratory (NPL). The graphite calorimeter allows a more direct calibration of HDR ~(192)Ir sources in terms of absorbed dose rate to water at a distance of 1 cm, D_(w,1 cm), compared with the current air kerma-based calibration method, where D_(w,1 cm) 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, D_(w,1 cm) 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 ~(192)Ir source was calibrated with the calorimeter in terms of D_(w,1 cm). The same source was also calibrated with NPL's HDR ~(192)Ir air kerma primary standard in terms of reference air kerma rate. Combining both measurements yielded the experimentally determined dose rate constant of the ~(192)Ir source.