S2761
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
findings suggest that PSMA PET may offer unique advantages in glioma radiotherapy, warranting further clinical research to optimize treatment strategies. References: 1. Lavanya V, Malik IM, Nallapareddy K, Srivastava M, Valiyaveettil D, Ahmed SF. Correlation of Target Volumes on Magnetic Resonance Imaging and Prostate-Specific Membrane Antigen Brain Scans in the Treatment Planning of Glioblastomas. Indian J Nucl Med IJNM Off J Soc Nucl Med India. 2022;37(3):245–8.2. Ş ahin M, Akgun E, Sirolu S, Can G, Sayman HB, Oner Dincbas F. Is there any additional benefit of 68Ga- PSMA PET on radiotherapy target volume definition in patients with glioblastoma? Br J Radiol. 2022 Oct 1;95(1139):20220049.3. Sasikumar A, Kashyap R, Joy A, Charan Patro K, Bhattacharya P, Reddy Pilaka VK, et al. Utility of 68Ga-PSMA-11 PET/CT in Imaging of Glioma-A Pilot Study. Clin Nucl Med. 2018 Sep;43(9):e304–9. Keywords: glioblastoma, PSMA PET CT, volumetric comparison Digital Poster 231 Clinical evaluation of the efficacy of AI-Based contouring software for delineating organs at risk for Gynaecological Radiotherapy Carys L Upton 1 , William van den Berg 1 , Alex Robinson 2 1 Radiotherapy, Barts Health NHS Trust, London, United Kingdom. 2 Radiotherapy & Oncology, Sheffield Hallam University, Sheffield, United Kingdom Purpose/Objective: Within the United Kingdom, Gynaecological cancers account for around 4.79 % of all cancer diagnoses1, with radical treatment options comprising of a variety of modalities including radiotherapy. In order to produce effective treatment plans, organs at risk (OAR) and target volumes need to be accurately delineated. Recently, AI-based contouring tools have been developed to assist or replace manual delineation, offering potential advantages such as reduced contouring time, improved workflow, and cost savings. However, local validation is necessary to ensure clinical suitability. Material/Methods: This retrospective service evaluation employed a repeated measures study design. Planning CT datasets from 20 patients who had previously undergone radical treatment for cervical or endometrial cancer (10 with intact female reproductive organs, 10 post- hysterectomy) were randomly selected. OAR structures included the bladder, rectum, sigmoid, and bowel bag. Manual contouring times were recorded for each structure and each patient, with Limbus (v1.8) AI contouring software later applied to the same
GTV_CAVITY defined in MRI guided segmentation with BTV defined in PSMA PET guided segmentation and difference in respective CTV and PTV. Material/Methods: This is a prospective comparative observational study includes 30 patients with histopathologically confirmed WHO Grade 3 or 4 gliomas. Each patient will undergo CEMRI brain and PSMA PET-CT for target delineation. Post op GTV_CAVITY (cavity + residual) and GTV_EDEMA (GTV_CAVITY + edema) will be defined on CEMRI, CTV_46 will be GTV_EDEMA + 2cm margin, CTV_60 will GTV_EDEMA + 2cm margin as per NRG guideline. Biological Tumour Volume (BTV) cavity + residual on PET will be mapped on PSMA PET-CT, CTV_B will be BTV + 2cm margin. A volumetric comparison with Dice Similarity Coefficient (DSC) will be performed to assess differences in target volumes. Results: The median GTV_CAVITY volume is 54.57cc (range: 14.43 – 104.16), median GTV_EDEMA volume is 107.05cc (range: 14.43 – 242.56), and median BTV volume is 70.28cc (range: 26.22 – 158.89).Median GTV_CAVITY – BTV is 6.58cc (0.84-46.64) and GTV_EDEMA -BTV is 23.62cc (2.97-193.92).For GTV_CAVITY – BTV, GTV_EDEMA – BTV, CTV_60 – CTV_B, CTV_46 – CTV_B; mean DSC values are 0.75, 0.69, 0.86, 0.82 respectively (p < 0.001), [Wilcoxon signed-rank test]. Subgroup analysis shows MGMT promoter methylated group has better agreement between MRI and PSMA based contouring than non methylated group. mean DSC of CTV_CAVITY and BTV for MGMT methylated and non methylated is 0.74 and 0.70 respectively.
Conclusion: These results highlight meaningful differences in MRI- guided and PSMA PET-guided target delineation, suggesting these imaging techniques produce distinct segmentation and treatment planning outcomes. The
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