Measurements of the high dose rate brachytherapy 192Ir source reference air kerma rate: a retrospective analysis of the single institution results

Tomislav Bokulić; Mirjana Budanec; Iva Mrčela; Marin Gregov; Ante Matanić; Vera Vujasinović; Mihaela Mlinarić

doi:10.1016/j.apradiso.2025.111959

Measurements of the high dose rate brachytherapy ¹⁹²Ir source reference air kerma rate: a retrospective analysis of the single institution results

Appl Radiat Isot. 2025 Jun 6:225:111959. doi: 10.1016/j.apradiso.2025.111959. Online ahead of print.

Authors

Tomislav Bokulić¹, Mirjana Budanec², Iva Mrčela², Marin Gregov², Ante Matanić², Vera Vujasinović², Mihaela Mlinarić³

Affiliations

¹ Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, 10000, Zagreb, Croatia. Electronic address: tbokulic@phy.hr.
² Department of Medical Physics, Sestre Milosrdnice University Hospital Centre, Vinogradska 29, 10000, Zagreb, Croatia.
³ Specialty Hospital Radiochirurgia Zagreb, Ulica dr. Franje Tuđmana 4, 10431, Sveta Nedelja, 1000, Zagreb, Croatia.

PMID: 40499324
DOI: 10.1016/j.apradiso.2025.111959

Abstract

This work reports on the experiences and results of a single radiotherapy centre in over twenty years of well-type ionisation chamber reference air kerma rate (RAKR) measurements of two models ¹⁹²Ir high dose rate brachytherapy (HDRBT) sources. Quality assurance (QA) programmes worldwide recommend determining the RAKR of sources before being used in patient treatment. The observed discrepancies between the measured RAKR and the manufacturer's stated RAKR were analysed. A systematic analysis of the data was used to calculate the uncertainty budget. Measurement procedures and conditions were adjusted during the time to warrant accurate and consistent results. The RAKR uncertainty budget was estimated by examining all contributions to the model equation for calculating RAKR from measured signals. The mean percentage difference between the measured RAKR and the manufacturer's certificate value of 0.32 % ± 0.97 % was obtained. An analysis of these differences revealed a potential drift in chamber sensitivity over time and a shift in results following the introduction of a new chamber. Nevertheless, all observed differences were within the 3 % tolerance level and 85 % within the 1.5 % level. The overall expanded uncertainty of the measured RAKR of the HDRBT ¹⁹²Ir source of 3.04 % (k = 2) was estimated. Independent determination of RAKR of an HDRBT source is crucial for accurate and reliable brachytherapy treatments. A detailed analysis of the uncertainties associated with RAKR measurements is indispensable for an appropriate understanding of the sources of uncertainty, means of their reduction, and any adjustments needed for clinical QA programmes.

Keywords: HDR brachytherapy; Reference air kerma rate; Well-type ionisation chamber.