A common method of a new HDR source calibration is to measure a maximum ionization current (Imax) using a well ionization chamber, in which the 192Ir source travels along the chamber axis in the spatial domain. The source’s air-kerma strength (SK) can be determined from the measured Imax. In this work, an approach for routine calibration of the air-kerma strength of an HDR 192Ir source in the temporal domain using integrated charge measurements with a well ionization chamber is presented. The charge Q (t) is measured as a function of time (t) for different dwell times at a sweet spot position in the well ionization chamber. The air-kerma strength is obtained from the slope (dQ/dt) of charge linearity measurement derived from the relationship between total ionization charge and time. This paper compares this method with the commonly used calibration approach based on measuring the maximum ionization current Imax in the well chamber. The agreement between these two methods of calibrating the 192Ir source over the past several years is good and differences are less than 1%, the key finding of this study. The effect of the sweet spot range in the chamber is measured and the transit time is analyzed. New dQ/dt data over the past few years are presented. This paper provides detailed data on the sweet spot regions, transit time, and sensitivities for two types of well-type ionization chambers, and discusses the application in HDR 192Ir source exchanges. This dQ/dt method provides additional support to 192Ir sources calibration and verification.
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