ESTRO 2025 - Abstract Book

S3317

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

The statistical distribution of the analyzed DVH parameters is illustrated in figure 1. Marginal differences can be observed between the algorithms for all three contours under investigation. Table 1 summarizes the outcomes of statistical testing. The differences between the planned dose and all algorithms are significant for the CTV and rectum, while most of the algorithms do not have significant differences with each other. Few significant differences were observed in the CTV V95% for most algorithms, with MIM and differences with the planned dose being noteworthy exceptions. For D1CC in the bladder, statistically significant differences mainly occur between MIM and Elastix versus the other algorithms. The significant differences in D1CC in the rectum are more prominent, with CMM, HS and the planned dose being most noteworthy. Conclusion: While statistically some differences are present between the algorithms, in absolute terms these are small and may become negligible, particularly for the bladder and rectum. Therefore, from a practical perspective, any of the investigated solutions could be considered for use in a clinical workflow to account for intra-fraction motion in patients undergoing prostate MRIgRT.

Keywords: dose accumulation, MRIgRT

References: [1] Bosma, L. S., Zachiu, C., Ries, M., De Senneville, B. D., & Raaymakers, B. W. (2021). Quantitative investigation of dose accumulation errors from intra-fraction motion in MRgRT for prostate cancer. Physics in Medicine and Biology, 66(6), 065002. https://doi.org/10.1088/1361-6560/abe02a

3577

Poster Discussion Breath-Hold Proton Therapy for Mediastinal Lymphoma with Surface Scanning and Nasal High-Flow: One Year Clinical Experience Gloria Vilches-Freixas, Kim van der Klugt, Richard Canters, Esther Kneepkens, Fleur Vereijken, Maud Cobben, Maud van den Bosch, Indra Lubken, Anne van Engelen, Cissy Stultiens, Marije Velders, Giorgio Cartechini, Maaike Berbée, Bastiaan Ta Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands Purpose/Objective: We report the first clinical experience treating mediastinal lymphoma patients in breath-hold (BH) with intensity modulated proton therapy (IMPT) using surface-scanning (SS) for beam gating and nasal high-flow therapy (NHFT) to enhance BH duration and stability. Material/Methods: Since December 2023, seven mediastinal lymphoma patients were treated with IMPT in BH, i.e. supported by SS and NFHT with 40 liters/minute and 21% O 2 . Patients qualified for IMPT based on reduction of acute coronary effects, and/or risk reduction of secondary breast and lung cancer. Patients were positioned on an inclined board to achieve a better SS field-of-view, and treatment plans consisted of 3-4 anterior beams. Each beam was automatically gated using SS, with a breathing window of 3 mm and a maximum allowed isocenter shift of 5 mm. SS respiratory traces were synchronized with beam delivery data extracted from machine log-files. Then, BH stability, BH duration, and isocenter shifts during the daily cone-beam CT (CBCT) and during treatment were determined (Fig.1). To evaluate the residual clinical target volume (CTV) motion and the feasibility of a margin reduction in BH, an additional post treatment CBCT was acquired for 17 fractions (2-3 per patient). To account for possible anatomical changes that would trigger a plan adaptation, a weekly repeated CT (reCT) followed by a dose recalculation and a robust plan evaluation was performed for each patient.