Calibration of well type ionization chambers for High Dose Rate (HDR) 192Ir quality

The IAEA has provided well type chambers to Secondary Standard Dosimetry Laboratories (SSDLs) and to radiotherapy centres since few years. The initial calibration of the chambers for LDR 137Cs and HDR 192Ir qualities is made by the Accredited Dosimetry Calibration Laboratory (ADCL) at the University of Wisconsin, USA. The IAEA TECDOC-1079 recommends that well type chambers should be calibrated every 5 years or when indicated by the periodic constancy checks. The re-calibration for LDR 137Cs quality can be obtained from the IAEA Dosimetry Laboratory. However, the IAEA Dosimetry Laboratory does not maintain standards for HDR 192Ir quality and cannot do so within a foreseeable future because of the high costs associated with it. Those SSDLs that have a calibration service for (HDR) 192Ir quality and need to re-calibrate the well type chamber may do so by sending the chamber to the ADCL mentioned above. This, however, is related with relatively high costs that may be an obstacle for some SSDLs. This means that some SSDLs are faced with problems: the needs of providing traceable calibrations to the radiotherapy centres and at the same time keeping the metrological quality at the highest possible level