S2358
Physics - Quality assurance and auditing
ESTRO 2026
Cancer Centre, Northwood, United Kingdom. 8 Clinical Oncology, St James’s University Hospital, Leeds, United Kingdom. 9 Leeds Institute of Medical Research, University of Leeds, Leeds, United Kingdom Purpose/Objective: The APPROACH (Analysis of Proton vs Photon Radiotherapy in Oligodendroglioma and Assessments of Cognitive Health) trial protocol mandates delineation of organs of interest with optimal dose guidance, including the hippocampus and the hypothalamus. This will allow future analysis of dose received by these structures, to correlate with the assessment of late treatment related adverse events, including the primary endpoint of neurocognitive scoring. Here we review trial centres’ previous experience in contouring the hippocampi and hypothalamus and assess performance in the benchmark outlining case. Material/Methods: The APPROACH trial included a comprehensive radiotherapy quality assurance (RTQA) programme. Pre-trial elements include a facility questionnaire (FQ) to document local radiotherapy practices and confirm ability to comply with the trial protocol. Participating centres also completed benchmark outlining and planning cases in accordance with the APPROACH Radiotherapy Guidance. Between December 2022 and September 2025, the FQ was circulated to 23 photon and 2 proton beam radiotherapy (PBT) centres in England and Wales. The benchmark case data included planning CT and MRI (using thin slice (~1mm) volumetric sequences). Atlases were created by the RTQA Radiation Oncologists to guide hippocampus and hypothalamus contouring. Submitted hippocampus and hypothalamus contours were evaluated for concordance against expert-defined consensus gold standard (GS) volumes using conformity indices (CIs): discordance index (DI), geographical miss index (GMI), Jaccard index (JCI) and mean distance to conformity (MDC). Results: All FQs were returned. The FQ revealed that 6/25 centres routinely contour the hippocampus. Only one PBT centre routinely contours the hypothalamus. Benchmark case contours were submitted by 20 centres. Median conformity indices are shown in Table 1. JCI > 0.7 is generally considered the cut-off to denote acceptable conformity.
Slice by slice analysis showed that the superior and inferior extent of the structures were more prone to deviations from the GS. Figure 1 shows each centres' MDC for the left hippocampus.
Conclusion: Analysis of the APPROACH pre-trial QA indicates that hippocampi and hypothalamus are infrequently contoured in standard practice. The outlining benchmark case highlights the interobserver variation that exists in contouring, despite provision of specific, atlas-based guidance. Conformity indices demonstrated moderate agreement with a median JCI of 0.61 for hippocampi and 0.51 for hypothalamus with both under- and over-contouring observedThe trial has implemented prospective contour review for all patients in the APPROACH trial to confirm adherence to protocol and ensure validity of trial results. References: Gwynne S, et al. Improving radiotherapy quality assurance in clinical trials: assessment of target volume delineation of the pre-accrual benchmark case. Br J Radiol. 2013 Apr;86(1024):20120398. doi: 10.1259/bjr.20120398.Lorenzen EL, et al. A national study on the inter-observer variability in the delineation of organs at risk in the brain. Acta Oncol. 2021 Nov;60(11):1548-1554. doi: 10.1080/0284186X.2021.1975813. Slevin F, et al. APPROACH: Analysis of Proton versus Photon Radiotherapy in Oligodendroglioma and Assessment of Cognitive Health - study protocol paper for a phase III multicentre, open-label randomised controlled trial. BMJ Open. 2025 Feb 26;15(2):e097810. doi:
Made with FlippingBook - Share PDF online