S133
Brachytherapy - Physics
ESTRO 2026
international coordinated research project. Material/Methods:
Monte Carlo (MC) simulations (RapidBrachyMCTPS, Geant 4) were performed with a PMMA phantom of 10 × 6 × 5 cm3 with clinical applicators to calculate correction factors for the lack of scatter (ks) resulting from the limited size of the phantom, non-water equivalence of the phantom (km) applicator materials (ka), and table backscatter (kb) to account for deviations from TG-43 conditions [1,2]. Reference plans, with a dose of 7 Gy to point-A were used (SagiPlan v2.1 Bebig Medical, Germany, Bebig Ir2.A85- 2 and Oncentra v4.7, Veenendaal, Netherlands, Flexisource HDR Ir-192). Absorbed dose to the medium was scored in 2.5 × 2.5 × 2.5 mm3 voxels and 5 × 107 primary particles were simulated.The MC simulated correction factors obtained for the three applicators (Bebig CT/MR Ring &Tandem, Elekta Venezia and Geneva) were experimentally validated. Four radiochromic films (EBT-4, Ashland, USA) were placed at 20 mm (left and right, point-A planes) and at 25 mm (anterior and posterior, bladder and rectum planes) from the tandem (Fig 1). Doses were evaluated, using the obtained MC correction factors, in a total of 32 points (2.5 × 2.5 mm2) per applicator along the central profile of the films in clinically relevant equally spaced points and compared to the TPS (DTPS/DFilm).
Conclusion: This commissioning and validation of micro-silica TLD beads supports their feasibility of use for IVD in HDR brachytherapy. Future work will include the commissioning of 1.0 mm beads for the use of IVD within interstitial needles. Keywords: Internal In-vivo Dosimetry, Brachytherapy References: [1] M. Masterson, G. Wood-Stott, S. M. Jafari and D. Bradley, “A review of micro silica beads in radiation dosimetry applications,” Radiation Physics and Chemistry, vol. 200, 2022. [2] S. Babaloui, S. Jafari, A. L. Palmer, W. Polak, A. Sheidaei, A. Shirazi, A. Lohstroh and R. Jaberi, “Using micro silica bead TLDs in high dose rate brachytherapy dosimetry: A Phantom Study,” Radiation Physics and Chemistry, vol. 191, 2022. Monte Carlo calculated correction factors and experimental validation for an end-to-end dosimetry audit for gynaecological brachytherapy Krzysztof Chelminski 1 , Liset de la Fuente Rosales 1 , Maria del Sol Quintero Castelan 1 , Benjamin Kellogg 1 , Abigael Kibet 1 , Divyanshi Divyanshi 1 , Alexis Dimitriadis 1 , Jonathan Kalinowski 2,3 , Shirin Abbasi Enger 2,3 , Mauro Carrara 1 , Jamema Swamidas 1 1 Department of Nuclear Sciences and Applications, IAEA - International Atomic Energy Agency, Vienna, Austria. 2 Department of Oncology, McGill University, Montreal, Canada. 3 Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Canada Purpose/Objective: End-to-end (ETE) dosimetry audits have the potential to evaluate systematic and procedural errors that may not be detected by routine quality control, particularly where modern image-guided techniques demand high precision. The aim of this study was to obtain and validate correction factors for a phantom designed for ETE dosimetry audits under the framework of an Digital Poster Highlight 3097
Results: The mean (±SD) dose ratio (DTPS/DFilm) for a total of 96 evaluation points for all applicators was 0.95 (±0.05), while the corresponding figure for each applicator was: Bebig CT/MR Ring &Tandem 0.94 ± 0.05, Elekta Venezia 0.97 ± 0.02 and Elekta Geneva 0.94 ± 0.04. Dose deviations in regions with steep dose gradients and low doses require additional consideration for dose evaluation uncertainty in films. The major influencing factors are applicator and phantom material, and the surrounding medium, while HE SolidWater used as backscatter table material was negligible (Table). The combined uncertainty (k=2) of film dose evaluation was estimated as 4.6% and MC simulations as 1.6%.
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