ESTRO 2025 - Abstract Book

S700

Clinical - CNS

ESTRO 2025

2. Grosu AL, Weber WA, Graf E, Mix M, Wiehle R, Nestle U et al. PET vs. MRI based reirradiation in glioblastoma. A prospective randomized trial (GLIAA, NCT01252459). Oral presentation at ESTRO 2024, Glasgow 3.-7. May 2024.

2404

Digital Poster Inter-observer variability in glioblastoma target delineation – A national study

Anders Schwartz Vittrup 1 , Camilla Skinnerup Byskov 1 , Aida Muhic 2 , Mikkel Skaarup 2 , Rikke Hedegaard Dahlrot 3 , Søren Nielsen Agergaard 3 , Christian Rønn Hansen 3 , Charlotte Aaquist Haslund 4 , Thomas Overgaard Kristensen 4 , Morten Høyer 5 , Kim Møller Hochreuter 5 , Jesper Folsted Kallehauge 5 , Slavka Lukacova 1 1 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Oncology, Rigshospitalet, Copenhagen, Denmark. 3 Department of Oncology, Odense University Hospital, Odense, Denmark. 4 Department of Oncology, Aalborg University Hospital, Aalborg, Denmark. 5 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: The Danish Neuro Oncology Group (DNOG) has established national consensus guidelines for delineating gross tumour volume (GTV) in glioblastoma based on recently published EANO-ESTRO guidelines (1). The study was conducted by expert observers to evaluate the inter-observer variability of the delineated GTV structures. Material/Methods: Ten patients with contrast enhancing glioblastoma (WHO2021) were selected, and GTVs were delineated by six experts from all five centres treating primary brain tumours in Denmark. Either a postoperative MRI (in case of surgical resection) or the most recent preoperative MRI (in case of biopsy) was rigidly co-registered with treatment planning MRI (T1w+C and T2 FLAIR). Radiological description was available for all diagnostic images. Dice Similarity Coefficient (DSC), Mean Surface Distance (MSD) and Hausdorff 95% distance (HD95) were used to compare the delineations. Results: Baseline characteristics of patients are shown in Table 1. Median age was 65 (range 53-71) years. Methylguanine DNA methyltransferase (MGMT) promoter was methylated in five patients. Tumour was located in the temporal lobe in six patients. Gross tumour resection/partial resection/biopsy was performed in four/three/three patients. Three patients had a multifocal tumour. The median GTV was 17.5 (range 6.6 - 103.0) cm 3 . Across the patients, the median DSC and MSD were 0.89 (0.85 - 0.93) and 0.8 (0.5 - 1.6) mm, respectively, and the median HD95 was 2.2 (1.4 - 6.0) mm. In one patient, larger variations in median MSD (0.7 – 8.9 mm) and HD95 (2.0 – 43.0 mm) were observed, most likely due to the development of a satellite image change in the contralateral hemisphere postoperatively, which was missed by two experts (Figure 1).