ESTRO 2025 - Abstract Book

S323

Brachytherapy - Physics

ESTRO 2025

1200

Mini-Oral Temporal Drift in Ir-192 source strength measurements. A BRAPHYQS Multi-center analysis

Javier Vijande 1,2,3 , Marisol De Brabandere 4 , Taran Hellebust 5 , Antonio Herreros 6,7 , Jacob G. Johansen 8,9 , Christia Kirisits 10 , Ruud van Leeuwen 11 , Panagiotis Papagiannis 12 , Mark J. Rivard 13 , Frank-André Siebert 14 , Frank Verhaegen 15 , Jan Wiersma 16 , Åsa Carlsson Tedgren 17,18,19 1 Departamento de Física Atómica, Molecular y Nuclear, Universitat de Valencia, Burjassot, Spain. 2 Unidad Mixta de Investigación en Radiofísica e Instrumentación Nuclear en Medicina (IRIMED),, Instituto de Investigación Sanitaria La Fe (IIS-La Fe)—Universitat de Valencia (UV), Valencia, Spain. 3 Instituto de Física Corpuscular, IFIC (UV-CSIC), Burjassot, Spain. 4 Dept. of Radiation Oncology, University Hospital Gasthuisberg, Leuven, Belgium. 5 Department of Oncology, The Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway. 6 Fonaments Clinics Department,, Universitat de Barcelona, Barcelona, Spain. 7 Radiation Oncology Department, Hospital Clínic-Universitat de Barcelona, Barcelona, Spain. 8 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 9 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. 10 Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Vienna, Austria. 11 Department of Radiation Oncology, Radboud University Medical Center, Nijmegen, Netherlands. 12 Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Athens, Greece. 13 Department of Radiation Oncology, Alpert Medical School of Brown University, Providence, USA. 14 UKSH, Campus Kiel, Klinik für Strahlentherapie (Radioonkologie), Kiel, Germany. 15 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands. 16 Radiation Oncology, Amsterdam UMC location University of Amsterdam, Amsterdam, Netherlands. 17 Radiation Physics, Department of Medicine and Health (IMH), Linköping University, Linköping, Sweden. 18 Section of Radiotherapy Physics and Engineering, Medical Radiation Physics and Nuclear Medicine, Karolinska University hospital, Stockholm, Sweden. 19 Department of Oncology Pathology, Karolinska Institute, Stockholm, Sweden Purpose/Objective: Accurate reference air kerma rate (RAKR) certification values of the sources are essential for ensuring safe and effective dose delivery in brachytherapy (BT). Since the absorbed dose is directly proportional to RAKR, these discrepancies could impact patient outcomes. Recently, several institutes have observed an increasing deviation between their own RAKR measurements and the vendor-provided certificate value in Ir-192 BT. This study examines this trend in a multi-center study across Europe. Material/Methods: Data from over 1700 RAKR measurements conducted between 1997 and 2024 collected from 27 European institutions performing BT were included in this analysis. Centers used various BT afterloaders, sources and measurement systems calibrated at different standard laboratories, representing a broad spectrum of RAKR measurement practices. The vast majority of sources (and thereby certificate values) used in Europe are manufactured at the same institution regardless of the vendor. Linear regression models and residual analyses were applied to the temporal change in the differences between RAKR clinical measurements and source certificates. Analyses were segmented by source and in specific time periods based on updates in international calibration protocols. Results: A statistically significant temporal drift was observed in the difference between the institute-measured Ir-192 RAKR values and vendor certificates with an annual drift rate that increased to approximately 0.15%/year (see figure). Centers relying on different primary and secondary calibration laboratories experienced different shifts, aligning with staggered implementation of international calibration updates. The consistency in RAKR measurements across centers further highlighted the need for frequent recalibration to align with primary standards and updated protocols (Perez-Calatayud et al., 2022).