Author: Åsa K. Carlsson Tedgren, Taran Hellebust, Antonio Herreros, Jacob Johansen, Christian Kirisits, Panagiotis Papagiannis, Mark J. Rivard, Frank-Andre Siebert, Frank Verhaegen, Javier Vijande, Jan Wiersma, Marisol de Brabandere, Ruud van Leeuwen 👨🔬
Affiliation: UKSH, Campus Kiel, Klinik für Strahlentherapie (Radioonkologie), Department of Oncology, The Norwegian Radium Hospital, Oslo University Hospital, Radiation Physics, Department of Medicine and Health (IMH), Linköping University, Radiation Oncology Department, Hospital Clínic-Universitat de Barcelona, IDIBAPS, IFIC-UV, Radiation Oncology, Amsterdam UMC location University of Amsterdam, Department of Radiation Oncology, Radboud University Medical Center, Department of Oncology, Aarhus University Hospital, University Hospital Gasthuisberg, Dept. of Radiation Oncology, Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Department of Radiation Oncology (MAASTRO), GROW – School for Oncology and Reproduction, Maastricht University Medical Centre+, Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Warren Alpert Medical School of Brown University 🌍
Purpose: This study, which was carried out by the GEC-ESTRO BRAPHYQS working group, reports the increasing divergence between clinical reference air kerma rate (RAKR) measurements and vendor-provided certificate data for Ir-192 brachytherapy sources in Europe. Since RAKR is proportional to absorbed dose, discrepancies could have clinical implications. The aim is to quantify such temporal drift, investigate its origin and assess its potential impact.
Methods: Data from over 1.700 RAKR measurements between 1997 and 2024 at 28 European centers belonging to 8 different countries were analyzed. These institutions employed diverse afterloaders, sources, and measurement systems calibrated across various laboratories, reflecting the heterogeneity of clinical practices. Despite vendor differences, Ir-192 sources were produced at the same facility, which also issues the certificates. Linear regression models and residual analyses quantified the temporal drift. Analyses were stratified by source type to evaluate variability among centers. The impact of international calibration protocol updates and alignment with primary standards was also assessed.
Results: A statistically significant temporal drift in hospital-measured RAKR compared to vendor certificate values was identified. This drift corresponds to an annual increase of approximately 0.15% starting in 2017–2018. Consequently, the mean difference value rose from 0.05% before 2018 to 0.66% when considering recent measurements. Centers using different calibration laboratories reported variable shifts, highlighting potential discrepancies in the calibration chain's integrity.
Conclusion: The origin of the observed drift remains unclear. Initial investigations focused on the hypothesis that it was linked to recent updates in the PTB standard; however, this does not appear to explain the trend. Comprehensive efforts, including discussions with all relevant stakeholders, have been initiated to identify the underlying cause. The implications of this drift for dosimetric accuracy in brachytherapy are potentially significant. This work emphasizes the necessity for stringent calibration protocols to prevent dosimetric drift and ensure robust clinical implementation.