Author: Anna Becker, Tomislav Bokulic, Mauro Carrara, Krzysztof Chelminski, Larry A. DeWerd, Alexis Dimitriadis, Benjamin Kellogg, Malcolm R. McEwen, Zakithi L.M Msimang, Mark J. Rivard, Thorsten Sander, Thorsten Schneider, Jamema Swamidas, Egor Titovich, Paula Toroi, Carlos E. de Almeida, Jacco de Pooter, Liset de la Fuente Rosales, Deborah G. van der Merwe 👨🔬
Affiliation: Radiation and Nuclear Safety Authority, University of Zagreb, National Physical Laboratory, IAEA, Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin - Madison, Rio de Janeiro State University, Dosimetry Laboratory, Dosimetry and Medical Radiation Physics Section, Division of Human Health, International Atomic Energy Agency, Physikalisch-Technische Bundesanstalt, National Metrology Institute, University of the Witwatersrand, Dosimetry and Medical Radiation Physics Section, Division of Human Health, International Atomic Energy Agency, National Research Council, Warren Alpert Medical School of Brown University 🌍
Purpose: The recently published IAEA-TRS-492 international code of practice (CoP) aims at improving traceability, accuracy, and consistency in Brachytherapy Dosimetry. To assess current approaches to brachytherapy dosimetry worldwide and establish a baseline for the implementation strategy of this CoP, a survey of hospitals and Secondary Standards Dosimetry Laboratories (SSDLs) using High Dose Rate (HDR) brachytherapy was conducted.
Methods: HDR brachytherapy users in IAEA databases were invited to participate in the survey. The questions (n=52) were categorised into: equipment, calibration methods, dosimetry formalism, measurement quantities, and uncertainties.
Results: Responses were received from 311 centres in 85 countries. The main contributors were hospitals (89%) and SSDLs (10%).
The radionuclides reported were Ir-192 (83%) and Co-60 (17%). Traceability to an SSDL was reported by 56% of participants and to a Primary Standards Laboratory by 37%, while 7% stated none. For calibration, 72% send the entire measurement system every 21 to 31 months.
The reference quantities reported were RAKR (65%), AKS (29%), Apparent Activity (4%), and Dw (2%) and the CoPs in use are AAPM-TG-56 (26%), IAEA-TECDOC-1274 (26%), IAEA-TRS-492 (17%), national/regional guidance (25%) and others (e.g. manufacturer manual) (6%). For reference dosimetry, 96% of participants used well-type, while 4% used cylindrical ionisation chambers. 13% reported, that chamber commissioning was not performed prior to first use. The correction factors being applied were air density (79%), electrometer (76%), recombination (63%), polarity (47%), and humidity (19%).
23% reported a clinical source model different from the one used by the calibration laboratory. The source strength used in the TPS was adapted from the source certificate in 75% of cases. The combined uncertainty in source strength measurements ranged from 0.5% to 5.0% (k=2).
Conclusion: The survey highlighted the existence of some sub-optimal dosimetry practices and the need for harmonized implementation of the international CoP for brachytherapy dosimetry.