S1880
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
inaccuracies and 3) the superior inferior extend of the field-of-view (FOV). In the pilot phase, CT served as backup for surface guided patient setup and CBCT. Results: Target DVHs on sCT and CT showed excellent agreement, even in near-min and near max (D2%, D98%). OARs around the isocenter (rectum, bladder, sacrum) were well within reasonable limit, while we observed slightly larger dose deviation at the peripheral site (figure 1). This is due to limited FOV of the MRI and slight different patient position. FOV were 366 mm for MRI, while varied between 418-573 mm for CT. To enhance the usability of the MRI, T1 Dixon’s imaging isocenter were shifted 4 cm superior. Prostate fiducials were identified on the T1 Dixon opposing phase, complementing the sCT (figure 2). A 3D printed MR marker holder allowed identifying the baseplate position for proper attenuation information. Body contour showed no relevant differences, confirming the sCT is suitable for VisionRT (London, UK). CBCT- based position verification was also satisfactory, while the fiducial contours allowed proper alignment. Conclusion: The T1 Dixon sequence based synthetic CT demonstrated reliable substitute of the CT-based workflow. Implanted fiducial can be identified, along the proper patient positioning baseplate (with the of 3D printed accessory). Despite limited field-of-view, SGRT and CBCT-based IGRT remained fully effective. With these adaptations, MR-only workflows for pelvic radiotherapy can be introduced into clinical practice safely. References: [1] White Paper: MR-based Synthetic CT Reimagined — An AI-based Algorithm for Continuous Hounsfield Units in the Pelvis and Brain, with syngo.via RT Image Suite (VB60). Siemens Healthineers.[2] O’Connor, L. M., Choi, J. H., Dowling, J. A., Warren-Forward, H., Martin, J., & Greer, P. B. (2022). Comparison of synthetic computed tomography generation methods, incorporating male and female anatomical differences, for magnetic resonance imaging-only definitive pelvic radiotherapy. Frontiers in Oncology, 12, 822687.[3] Autret, D., Guillerminet, C., Roussel, A., et al. (2023). Comparison of four synthetic CT generators for brain and prostate MR-only workflow in
used with appropriate optimization strategies. References: 1) Dose Calculation Comparisons between Three Modern Treatment Planning Systemshttps://journals.lww.com/jomp/toc/2020/4503 02) Dosimetric comparison and evaluation of two computational algorithms in VMAT treatment plans.3)Rostami A, Neto AJC, Paloor SP et al. Comparison of four commercial dose - calculation algorithms in different evaluation tests. J X-ray Sci Technol. 2023;31(5):1013–10334) Ali A, Rshbek M, Mohamed A et al. Impact of different grid sizes and dose calculation algorithms on dosimetric parameters for head - and - neck IMRT. Egypt J Biophys Biomed Eng. 2024;25(1):13–23 Keywords: CCC, AAA, SIB Clinical implementation of pelvis sythentic CT: Limitations, opportunities and dosimetric results Salh Eddin Mohammed BOUDOUANi 1,2 , Akos GULYBAN 1 , Younes JOURANI 1 , Nick REYNAERT 1 , Nicolas JULLIAN 3 , nicolas PAULY 4 1 Medical physics, Institut Jules Bordet, Bruxelles, Belgium. 2 Medical physics, Cliniques de l’Europe, Bruxelles, Belgium. 3 Radiation Oncology, Institut Jules Bordet, Bruxelles, Belgium. 4 Nuclear Metrology Service, Université libre de Bruxelles, Bruxelles, Belgium Digital Poster 2258 Purpose/Objective: This study aimed to clinically introduce MR-only RT workflow for pelvis tumors, using a commercial synthetic CT (sCT) solution (syngo.via RT Image Suite, Siemens Healthineers, Erlangen, Germany) [1]. Primary objective was to assess dosimetric accuracy and validation, while secondary aim was to identify possible limitations, needs for workflow adaptations and opportunities in the entire workflow. Material/Methods: Between 2024 April and 2025 May forty pelvic cancer patients underwent treatment planning CT (Somatom goPro, Siemens) and MRI simulation (1.5T Magnetom Aera, Siemens), followed by a sCT generation using the T1 Dixon MR sequence. Treatment plans were created on CT (prescriptions : 47 Gy, 55 Gy, 60 Gy, and 67 Gy) and recalculated on sCT. DVHs were compared between the CT and sCT. Furthermore dose difference versus volume histograms and median dose difference per ROI (targets and OARs) were evaluated with a 2 % tolerance [2,3]. Concerning the MR only workflow, three main limitations were identified: 1) Lack of representation of the implanted fiducials on sCT, 2) lack of information about the patient positioning baseplate, which could lead to dosimetric
radiotherapy. Radiation Oncology, 18, 146. Keywords: synthetic CT, MRI-only, prostate.
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