ESTRO 2025 - Abstract Book

S3598

Physics - Quality assurance and auditing

ESTRO 2025

Figure 1. The 3D-design of the dosimeter holder developed (A) and three 3D-printed holders compatible with Exradin W1, Razor Diode and RPLD from left to right (B).

Conclusion: The novel 3D-printed holder is a correction-less, universally compatible solution for positioning RPLDs in reference conditions for both photon and electron beams to conduct postal reference dosimetry audits. The holder design can provide enhanced measurement accuracy whilst reducing the audit kit size and the need for two separate holder systems for photons and electrons. In-house 3D-printing may also enable manufacture and shipping cost savings. This design enables efficient audit logistics and supports broader accessibility for institutions worldwide. An international multicentre study across different beam types and settings is currently being undertaken to provide user feedback on its usability. References: 1. Kazantsev, Pavel, et al. "Experimental determination of the standard IAEA holder correction factor for RPLD postal dose audit applications." Proceedings of the 8th Alpe-Adria Medical Physics Conference, Serb. Assoc. Med. Phys., Soc. Rad. Prot. Serb. Monten., Vinca Inst. Nuc. Sci., Borislav Grubor, Novi Sad, Serbia. 2017. 2. Dimitriadis, Alexis, et al. "IAEA/WHO postal dosimetry audit methodology for electron beams using radio photoluminescent dosimeters." Medical Physics 50.11 (2023): 7214-7221. 3. International Atomic Energy Agency, Absorbed Dose Determination in External Beam Radiotherapy, Technical Reports Series No. 398 (Rev. 1), Vienna (2024) Keywords: 3D-print, reference dosimetry, postal audits

1134

Mini-Oral Efficient, Accurate, and Safe Detector-Less Patient-Specific QA Lars Hjorth Præstegaard Department of Oncology, Aarhus University Hospital, Aarhus, Denmark

Purpose/Objective: In radiotherapy, patient-specific quality assurance (PSQA) is essential for validating dose plans before treatment [1,2]. PSQA typically involves the comparison of TPS dose with measured dose using a 2D detector array [1,2,4-5]. Unfortunately, detector-based PSQA has several limitations (e.g., detector spacing and detector issues) that increase measurement uncertainty. In addition, detector-based PSQA is time-consuming and cannot distinguish between TPS errors, plan transfer errors, treatment delivery errors, and detector errors. This study investigates an efficient and accurate detector-less PSQA procedure. Material/Methods: Our clinic has more than 4 years’ experience with a detector-less PSQA procedure: 1) Calculation of various plan complexity metrics (PCMs) (e.g., MU-weighted average MLC leaf opening (MLCLO)) 2) Accurate independent secondary dose calculation (SciMoCa 1.7.2, Monte Carlo-based)

3) Treatment log file analysis (in-house-developed software) 4) Comprehensive machine QA (e.g., validation of log files)

The primary TPS is Varian Eclipse 16.5, and log files are from Varian TrueBeam/Clinac. Plans with out-of-tolerance PCMs are modified (e.g., fluence smoothing) in order to reduce primary/secondary dose calculation deviations, plan variability, and plan robustness issues.