S38
Brachytherapy - General brachytherapy
ESTRO 2026
Trueinvivo®, clinicians, and physicists. One- dimensional arrays were inserted into 18–20 Fr urinary catheters for urethral dose verification. Rectal doses were measured using either a fixed cylindrical probe or a Foley-catheter-based linear array. All dosimeters were CT/MRI compatible, prepared and analysed by Trueinvivo®, and read using a Harshaw 4500 reader.TLD-measured doses were compared with TPS- calculated values. CT scans were registered to MRI datasets for TLD localisation and TPS extraction. Linear interpolation aligned measurement positions. Agreement was assessed using percentage dose differences, Bland–Altman, and one-dimensional gamma analyses. Results: Urethral measurements: Across patients 2–8 ( ≈ 650 readings), 87% of TLDs were within ±10%, 94% within ±15%, and 98% within ±20% of TPS doses. Gamma analysis (3%/3 mm, 10% threshold) showed moderate concordance (mean pass rate 60% ±19%, mean γ = 1.04 ±0.32). Best agreement occurred in patient 2 (91% pass, γ = 0.53); poorest in patient 6 (29%, γ = 1.37).
planning. Keywords: Treatment Planning System, Python, Benchmarking References: 1. J. A. M. Cunha, R. Flynn, C. Bélanger, C. Callaghan, Y. Kim, X. Jia, Z. Chen, L. Beaulieu, Brachytherapy Future Directions, Seminars in Radiation Oncology 30 (2020) 94–106.2. S. Wuyckens, D. Dasnoy, G. Janssens, V. Hamaide, M. Huet, E. Loÿen, G. R. de Hertaing, B. Macq, E. Sterpin, J. A. Lee, K. Souris, S. Deffet, Opentps – open-source treatment planning system for research in proton therapy, 20233. J. Kalinowski, S. A. Enger, RapidBrachyTG43: A Geant4 - based TG - 43 parameter and dose calculation module for brachytherapy dosimetry, Medical Physics 51 (2024) 3746–3754. Z. M. C. Baum, Shaheer U. Saeed, Z. Min, Yipeng Hu, D. C. Barratt, MR to Ultrasound Registration for Prostate Challenge, 2023. https://zenodo.org/record/8004388 A clinical feasibility study of in vivo dosimetry using micro silica bead TLD arrays (DOSEmapper™) in HDR brachytherapy Amani A Chowdhury 1 , William Hamblyn 1 , Gerry Lowe 1 , Rachel Wills 1 , Roberto Alonzi 1 , Mohammed Abdul- Latif 1 , Robert Hughes 1 , Milan Anjanappa 1 , Hannah Tharmalingam 1 , Peter Ostler 1 , Gillian Marks 1 , Fatemeh Nazari 2 , Shakardokht M Jafari 2 , Peter Hoskin 1,3 1 Department of Radiotherapy, Mount Vernon Cancer Centre, Northwood, United Kingdom. 2 Trueinvivo, Trueinvivo, Portsmouth, United Kingdom. 3 Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom Purpose/Objective: In vivo dosimetry (IVD) independently verifies delivered dose during radiation therapy and is particularly valuable in high-dose-rate (HDR) brachytherapy, where steep dose gradients, large fraction sizes, and complex workflows challenge dose accuracy. Although recognised for quality assurance, clinical adoption remains limited by technical and workflow barriers [1]. This study evaluated the accuracy of micro-silica bead thermoluminescence dosimeters (TLDs) and assessed the feasibility of integrating IVD into the HDR brachytherapy workflow. Material/Methods: Following in-house commissioning of the Trueinvivo® (Portsmouth, UK) micro-silica TLD system (DOSEmapper™) a single-centre feasibility study Digital Poster 2425 (ClinicalTrials.gov NCT06863090) was initiated. Eight of twenty participants have been recruited; results are reported for seven patients (2–8) undergoing prostate boost HDR brachytherapy.Custom DOSEmapper™ arrays were designed collaboratively between
Rectal measurements: Non-spatial probe data (patients 2–3) showed mean absolute differences of 1.16 and 0.81 Gy. Catheter-array data (patients 5–8) showed mean differences 0.26–1.79 Gy (SD 0.23–0.94 Gy; limits ≈ ±1 Gy; n ≈ 315). Gamma pass rates varied 0– 67% (mean γ = 1.1–1.65). Measurements reflected dose in the rectal lumen rather than the wall, limiting clinical relevance.
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