S2125
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Digital Poster 1358 Evaluation of Daily Adaptive Radiotherapy for Bladder Cancer: Dosimetic outcomes and treatment time analysis Abdelaziz Tanji 1 , Naila Yada Laar 2 , Lydia Nyambe 2 , Naima Boumha 1 , Soufiane Majdoubi 1 , Ikram Nejjar 1 , Dounia Filali Benaceur 1 , Mohammed El Adnani Krabch 1 , latifa mesbah 1 1 Radiotherapy, Clinique d'Oncologie 16 Novembre, Rabat, Morocco. 2 Institut Superieur des Sciences de la Sante, University Hassan 1, Settat, Morocco Purpose/Objective: Bladder radiation therapy has traditionally relied on large planning target volumes (PTVs) to account for anatomical variations. The implementation of daily online adaptive radiotherapy (oART) allowed the reduction of PTV margins. This could yield to a significant reduction of organ at risk (OAR) dose.The objective of this study was to compare the dosimetric outcomes of conventional image-guided radiotherapy (IGRT) with those of oART. Material/Methods: Seven patients with muscle invasive bladder cancer received daily oART with Cone Beam CT (CBCT), artificial intelligence (AI)-assisted automatic delineation of the daily anatomy and online plan reoptimization. Prescribed doses were 64.5 Gy, 54 Gy, and 51 Gy in 30 to different Planning Target Volumes (PTVs). For each fraction, dosimetric data were collected from both scheduled (conventional IGRT) and adapted (ART) plans. Statistical comparisons were performed with the Wilcoxon signed-rank test, and significance was defined as p < 0.05.Bladder volume variability was assessed from daily cone-beam CT and the duration of the workflow was recorded. Results: Adapted plans consistently achieved superior PTV coverage, improved dose homogeneity, and better hotspot control compared to scheduled plans, with statistically significant differences across all dose levels (p < 0.001). Rectum and bowel sparing was improved in most patients, with only minor trade-offs in two cases. Marked inter-fractional bladder volume variations were observed, confirming the necessity of daily adaptation.
Conclusion: EPID-based IVD was successfully implemented in routine clinical workflow for both HN and lung radiotherapy. The system demonstrated high pass rates and robustness across different plan complexities. IVD effectively detected relevant anatomical and setup variations, confirming its value as a real-time quality assurance tool. For HN patients, the experience highlighted the importance of consistently immobilizing and blocking the shoulders with an adequate margin to ensure reproducibility. A larger study including more patients is planned to further investigate the relationship between plan complexity and gamma index results. References: 1) Nailon W, Welsh D, McDonald K, et al. J Appl Clin Med Phys. 2019 Jan;20(1):6-16 EPID-based in vivo dosimetry using Dosimetry Check™: Overview and clinical experience in a 5-yr study including breast, lung, prostate, and head and neck cancer patients2) Hernández V., Lara-Aristimuño I., Abella R., et al. Quantification of the Plan Aperture Modulation of Radiotherapy Treatment Plans. arXiv preprint arXiv:2410.02632 (2024)3) Mijnheer BJ, González P, Olaciregui-Ruiz I et al. Overview of 3-year experience with EPID-based in vivo dosimetry for IMRT and VMAT treatments. Pract Radiat Oncol. 2015 Nov- Dec;5(6):e679-87 Keywords: in-vivo dosimetry, H&N, lung
Table 1: Comparison of Rectum Dose Threshold Percentages Between Scheduled and Adapted Plans
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