Intercomparison of calibration procedures for Ir-192 HDR sources in The Netherlands and Belgium

Thirteen radiotherapy departments in The Netherlands and Belgium participated in an intercomparison of the calibration procedures in use for the quality control of iridium-192 high dose rate sources. A measuring device from 1 of the departments was taken to the 12 other participants, where 1-3 sources were measured by both the local and the visiting physicist's team. Also, 1 192Ir HDR reference source was taken to 7 other--Dutch--departments to serve as a stability check of the measuring device. The results of the local calibration were compared with the values obtained by the visiting team. A mean deviation of +1.3% was found in 19 observations, with values ranging from -0.4% to +3.0%. In total, 16 sources were checked. The measured reference air kerma rate of the available sources was compared with the value stated on the source calibration certificate: the values on the certificate were on the average +1.8% higher than the measured values, ranging from -4.2% to +6.8%. In 1 instance the reference source was also measured by The Netherlands Measurements Institute (NMI), the national standards laboratory in The Netherlands. A good agreement was found between the NMI calibration and the reference air kerma rate determined with the measuring device used in this project.