Audit on source strength determination for HDR and PDR 192Ir brachytherapy in Sweden

Background and purposeTo investigate the status of source strength determination in terms of reference air kerma rate (RAKR) for HDR and PDR 192Ir brachytherapy in Sweden.Materials and methodsRAKR was determined in each of the 14 Swedish afterloaders, using calibrated equipment from the Swedish Secondary Standard Dosimetry Laboratory.ResultsValues of RAKR from the external audit, the hospitals and vendors agreed within the uncertainty limits guaranteed by the vendors.ConclusionsThe accuracy in RAKR determination has increased over the last years as a result of increased availability of interpolation standards for HDR 192Ir and the increased use of robust well-type ion chambers designed for brachytherapy. It is recommended to establish a ratio between the RAKR value from own measurements at the hospital and that of the vendor since such a ratio embeds constant systematic differences due to e.g. varying traceability and therefore has the potential of being less uncertain than the RAKR alone. Traceability to primary standards for HDR 192Ir sources will in the future significantly decrease the uncertainty in RAKR of 192Ir brachytherapy.