ESTRO 2025 - Abstract Book

S3091

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Figure 1: Percentage differences between MRgXT and MRgPT for the mean value of relevant DVH parameters and the HI across all patients. A negative value indicates the reduction of the parameter when using MRgPT compared to MRgXT. Dashed lines show the median and the upper and lower quartiles. Conclusion: Offline adaptive MRgPT significantly reduces rectum and bladder dose and increases target dose homogeneity compared to online adaptive MRgXT in prostate cancer patients undergoing ultra-hypofractionated radiotherapy.

Keywords: MRgPT, MR-LINAC, prostate

References: [1] Zachow, D. (2023). Deep Learning zur Generierung neuartiger synthetischer Stopping Power Maps: Anwendung auf die Protonentherapie der Schädel- und Beckenregion. Master’s Thesis, TU Dresden.

960

Digital Poster Dosimetric advantages of daily online adaptive radiotherapy in patients undergoing chemoradiotherapy for esophageal cancer Thomas Weststate 1,2 , Leigh A.P. Bruijs 1,2 , Irma W.E.M. van Dijk 1,2 , Karin N. Goudschaal 1,2 , Zdenko van Kesteren 1,2 , Tezontl S. Rosario 1,2 , Jorrit Visser 1,2 , Joost J.C. Verhoeff 1,2 , Peter S.N. van Rossum 1,2 , Arjan Bel 1,2 1 Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 2 Cancer Center Amsterdam, Amsterdam UMC, Amsterdam, Netherlands Purpose/Objective: Neoadjuvant chemoradiotherapy (CRT) followed by surgery is a standard of care for locally advanced esophageal cancer [1, 2]. Current radiotherapy requires large PTV margins to compensate for interfraction anatomical variations, increasing the risk of radiation-associated toxicity to surrounding healthy tissues. Moreover, despite employing large margins, risk of missing the target remains due to possible tumor position variation. CBCT-based online adaptive radiotherapy (oART) might provide a solution through daily plan adaptation which accounts for interfractional anatomical changes, and enables margin reductions while maintaining target coverage. We aimed to assess the dosimetric advantages of daily oART compared to conventional image-guided radiotherapy in patients undergoing CRT for esophageal cancer.