S117
Brachytherapy - Physics
ESTRO 2026
the the applicator and the effective point of the detector is crucial. Therefore, a separate jig (B) has been manufactured to ensure accurate detector positioning (+/- 0.1 mm). The cavity depths h are adjusted to either z = 2.0 mm or z = 5.0 mm for different applicator sizes and detector types.
confidence. By combining articulating mechanics, image guidance, and inflatable conformal interfaces, it addresses nearly every documented limitation of the legacy Fletcher-Suit-Delclos (FSD) applicator lineage and its modern variants.Early-stage testing confirms feasibility, reproducibility, and compatibility across major imaging modalities. Ongoing work includes phantom validation and preparation for pilot clinical evaluation. The device aligns with the global shift toward minimally invasive, image-guided, precision- conformal radiotherapy. Conclusion: This innovation represents a paradigm shift in intracavitary brachytherapy delivery — combining the safety of endoscopic visualization, the adaptability of articulating mechanics, and the precision of conformal inflatable dosimetry. It is positioned to improve clinical outcomes, streamline workflow efficiency, and significantly elevate the global standard of care for cervical and uterine cancer treatment. Keywords: Endoscopic T and O, Brachytherapy, Cervical Cancer References: 1. International Agency for Research on Cancer. GLOBOCAN 2022: Global Cancer Observatory — Cancer Today. IARC/WHO, Lyon, France (2023). Available at: https://gco.iarc.fr New phantom for fast dosimetric quality assurance of ophthalmic Ru-106 / Rh-106 applicators Anna E Rintala, Assi K Valve, Vappu R E Reijonen, Mikko J Tenhunen Comprehensive Cancer Centre, Helsinki University Hospital, Helsinki, Finland Purpose/Objective: The diamond detector can be calibrated to measure absolute dose of Ru-106/Rh-106 ophthalmic applicators (1). In this work we present a new, lightweight miniphantom, Iris, for fast and precise quality assurance (QA) tests, eliminating the need for larger water phantoms. Material/Methods: The structure of the miniphantom is shown in Fig. 1. The phantom components are made from polymethyl metacrylate and can be filled with water. The design supports the use of either a PTW MicroDiamond detector or an IBA Diode detector (D), mounted in the holder H. A set of holders (A and P1-2) has been manufactured for precise positioning of applicators of different sizes. The current set supports Eckert & Ziegler Medical CCX, CCA and CCB Ru-106/Rh-106 applicators. The accuracy of the distance z between Poster Discussion 660
The diamond detector was calibrated in a linac electron beam for absolute dose measurements of Ru- 106/Rh-106 (1) in the water filled miniphantom. The diode detector was used for relative measurements in air. Two sets CCX / CCA / CCB Ru-106/Rh-106 applicators (from 2022 and 2024) were measured. Each measurement was repeated five times to estimate precision; between applicator exhanges all components were reassembled, and the detector was readjusted in the jig (B). For preirradiation of the diamond detector to a 10 Gy dose (~10 nC charge) to stabilize the leakage current, a separate jig for the PTW Sr-90 check source was constructed. Results: With the diamond detector an average agreement of 1 % to the manufacturer’s reference data was achieved: measured dose rate/reference = 0.99 ± 0.06 (mean ± SD), range 0.88–1.07. The QA measurement of one Ru- 106/Rh-106 applicator set of three applicators took less than 55 min with two 3 min charge integration time per applicator. We achieved 5 % precision/applicator, similarly as in relative measurements with the diode detector. As the sensitivity of the diode detector is higher (1 min charge integration is sufficient) and it needs shorter preirradiation than the diamond detector, the QA procedure is faster, around 30 min. Conclusion: The Iris miniphantom is a fast method for commissioning and dosimetric QA for Ru-106/Rh-106 applicators. Fixed detector positioning is a guarantee for accurate and repeatable measurements. Keywords: Ophthalmic applicators, QA, Dosimetry References: 1. Valve et al. Dose measurement of ophthalmic Ru-
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