Development of an Australian secondary standard for the reference air kerma rate measurement of 125I seeds

Calibration of a High-Dose-Rate 1000 Plus ionisation chamber and associated electrometer for the determination of reference air kerma rate for 125I brachytherapy seeds has been developed. Traceability was established from ionisation chamber measurements of an Amersham model 6711 125I seed for which a primary standard measurement of reference air kerma rate has been made by the National Institute of Standards and Technology. The status of an Australian secondary standard is to be realised by establishing legal verifying authority from the National Measurement Institute. The calibrated chamber thus provides a measurement from which similar chambers in hospitals may be calibrated. For quality assurance this result was compared with the calibration certificate supplied by the Accredited Dosimetry Calibration Laboratory of the University of Wisconsin, USA.