ESTRO 2025 - Abstract Book

S3329

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

ESTRO 2025

Conclusion: Bladder filling control via catheterization and volume monitoring maintains dosimetric accuracy in short-course rectal cancer treatments while minimizing infection risk.

Keywords: bladder filling ， MR-guided adaptive radiotherapy

References: [1]. Xi Feng, Bin Tang, Xinghong Yao, Min Liu, et al. Effectiveness of bladder filling control during online MR-guided adaptive radiotherapy for rectal cancer. Radiation Oncology . 2023;18(1)doi:10.1186/s13014-023-02315-3

3764

Poster Discussion Personalized Anisotropic Margin Strategy for Cervical Cancer Online Adaptive Radiation Therapy Haonan Xiao 1,2 , Qiufen Guo 1,3,4 , Junjie Ma 1 , Jian Chen 5 , Zhe Zhang 6 , Qian Wu 1 , Xiaohui Yan 1 , Jing Liu 1 , Lu Zhang 1 , Aihua Li 3 , Peng Xie 1 , Yong Yin 1 1 Radiation Oncology, Shandong Cancer Hospital and Institute, Jinan, China. 2 Shandong Provincial Key Medical and Health Laboratory of Pediatric Cancer Precision Radiotherapy, Shandong Cancer Hospital, Jinan, China. 3 Obstetrics and Gynaecology, Liao Cheng People’s Hospital, Liaocheng, China. 4 Cheeloo College of Medicine, Shandong University, Jinan, China. 5 Nuclear Science and Technology, University of South China, Hengyang, China. 6 Radiation Oncology, Peking University Shenzhen Hospital, Shenzhen, China Purpose/Objective: Online Adaptive radiation therapy (ART) has been an effective technique for managing patients' inter-fractional anatomical changes and therefore reduces planning target volume (PTV) [1-3]. However, online ART requires long on couch time for plan re-optimization and intra-fractional motions may increase. This study aims to develop and validate a personalized anisotropic margin strategy to address intra-fractional motion in cervical cancer online ART that minimizes the PTVs while maintaining the coverage of the clinical target volumes (CTVs). Material/Methods: Five patients were enrolled in this study. Each patient was prescribed a dose of 50.4 Gy delivered in 28 fractions and underwent two iterative cone-beam computed tomography (iCBCT) scans per fraction: one after positioning and another before beam delivery. Personalized anisotropic margins were calculated based on the intra-fractional motions of the CTV observed in the first five fractions of each patient. These margins were iteratively reduced in each direction (anterior, posterior, left, right, superior, and inferior) to minimize the resulting PTV while maintaining 99%