ESTRO 2025 - Abstract Book

S3530

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

(a) 3D water phantom inside the MR scanner. (b) Measured 2D dose distributions in water of deflected proton pencil beams at different energies. Results: The lateral beam deflection (distance from central beam axis) measured at positions A-E for energies between 100– 220 MeV shows agreement with TPS calculations within the measurement uncertainty of 3 mm (Fig. 1b). Example 2D dose distributions of deflected proton pencil beams measured pointwise with a microDiamond detector inside the water phantom for comparison with the TPS are shown in Fig.2b. Furthermore, the TPS reproduced the dose distributions for scanned fields at 100% gamma pass rate for a 3%/3mm(10%) acceptance criterion within the MR imaging volume (positions B-D) and measured absolute doses in patient fields were predicted with an accuracy of ±3%. Conclusion: The dose distributions and lateral beam shifts calculated by the TPS were found to be in good agreement with measured data. These promising results provide the basis for further in-depth validation and commissioning of the TPS with optimized experimental setups for future clinical use in MR-integrated proton therapy. Mini-Oral A 4D probabilistic uncertainty evaluation method to comprehensively assess plan robustness for esophageal IMPT cancer patients Jesus Rojo Santiago 1,2 , Steven J.M. Habraken 3,2 , Oscar Pastor-Serrano 4 , Yvonne Klaver 2 , Franziska Knuth 1 , Zoltán Perkó 5 , Mischa S. Hoogeman 1,2 1 Radiotherapy, Erasmus Medical Center Rotterdam, Rotterdam, Netherlands. 2 Medical Physics & Informatics, HollandPTC, Delft, Netherlands. 3 Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands. 4 Radiation Oncology, Stanford University, Palo Alto, USA. 5 Radiation Science & Technology, Delft University of Technology, Delft, Netherlands Purpose/Objective: For IMPT in esophageal cancer (EC) patients, the interplay effect arises from the interaction between respiratory induced tumor motion and the proton beam scanning. At our institute, EC IMPT patients are planned following the Dutch proton guidelines: a voxel-wise minimum (VWmin) dose evaluation across 28 scenarios to handle geometrical and range errors. Additionally, plans are assessed at the inhale/exhale 4DCT phases (In-4DpCT/Ex-4DpCT) to Keywords: proton therapy, MR-guided, TPS validation 3412