S2404
Physics - Quality assurance and auditing
ESTRO 2026
reliable GT and combining performance metrics with clinically relevant test scenarios. The resulting standardized methodology supports both single- centre and multi-centre workflows, enabling consistent, systematic comparison that can be adapted across different sites and applications. Keywords: DVH-of-the-Day, Synthetic CT, Contour propagation
using the gCTs and gStructs and compared to those calculated using the sCTs and uStructs from different
centres. Results:
Acceptable deviation for all dose metrics was defined as ±5% from the ground-truth (GT). Based on this threshold, D95% met the criterion in 90% of scenarios for CTV_6500, and in 84% of scenarios for the CTV_5400, indicating generally good agreement across centres. D98% was more sensitive to variations, with only 72% CTV_6500 and 66% CTV_5400 cases classified as acceptable. For the spinal cord D0.1cc, 86% of cases met the ±5% threshold, indicating generally good agreement across centres.Some unacceptable results were consistent between centres, indicating particularly challenging cases and/or issues with the GT used for validation. Others differed from centre-to- centre, with centres 1 and 3 producing more unacceptable results overall. Table 1 presents a summary of the results and Figure 1 shows examples of the DVHs-of-the-day.
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Evaluation and Selection of Film Dosimetry Analysis Software for Radiotherapy Dosimetry Audits: A Comparative Study Using Blind Dose Films Sherisse O Hunte 1 , Mark A D' Souza 2 , Brian Keller 2 , Andrew Nisbet 3 , Nikolay Zyuzikov 1 , Catharine Clark 4,5 1 Physics, University of the West Indies, St Augustine, Trinidad and Tobago. 2 Medical Physics, Odette Cancer Centre, Sunnybrook Hospital, Toronto, Canada. 3 Faculty of Engineering Sciences, University College London, London, United Kingdom. 4 Consultant Clinical Scientist, National Physical Laboratory (NPL), London, United Kingdom. 5 Medical Physics, University College London Hospitals NHS Foundation Trust, London, United Kingdom Purpose/Objective: Independent dosimetry audits are essential to radiotherapy quality assurance management and serve as a safeguard for accurate dose delivery. Radiochromic film is widely used in audit programs due to its high spatial resolution, near tissue equivalence and low energy and dose rate dependency. However, until recently (Beveridge et al., 2024) a standardized dose measurement reporting framework for radiochromic film had not been established. This study was conducted following the methodology described by Beveridge et al. to independently evaluate the accuracy, capability, and suitability of two film dosimetry analysis software systems—Software A (a commercial vendor-based package, Radiochromic.com) and Software B (an in- house developed Python program)—for application in an external audit program. Material/Methods: Calibration (0- 1000 cGy) and two blind dose Gafchromic™ EBT4 films were irradiated with 6 MV photon beams at a depth of 10 cm in a CIRS water slab phantom by the host institution and sent to the participating centre for analysis. The local film dosimetry protocol of the participant was followed with the two software systems described above with the mean and standard deviation for the two blind doses reported back to the host institution. An audit metric Q, Q= Droi/Dknown, was then calculated for
Conclusion: We developed a robust framework for the validation and QA of DVH-of-the-day. This included generating a
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