ESTRO 2025 - Abstract Book

S3312

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

ESTRO 2025

3552

Digital Poster Utilising bladder volume to predict intra-fractional motion of the CTV for cervical cancer patients undergoing radiotherapy Jasmine M Morrison 1 , Eliana Vasquez-Osorio 1 , Alan McWilliam 1 , Anthea Cree 2 , Peter Hoskin 3,1 , Marcel Van Herk 1 1 Division of Cancer Sciences, The University of Manchester, Manchester, United Kingdom. 2 Clinical Oncology, Clatterbridge Cancer Centre, Liverpool, United Kingdom. 3 Clinical Oncology, Mount Vernon Cancer Centre, Northwood, United Kingdom Purpose/Objective: External beam radiotherapy (EBRT) for cervical cancer targets the gross tumour volume (GTV), plus a clinical target volume (CTV) covering adjacent anatomical structures. Bladder volume fluctuations correlate with uterine movement for some patients, necessitating large (population-based) planning treatment volume (PTV) margins to ensure target volume coverage, increasing toxicity [1]. Daily adaptive radiotherapy allows treatment plan optimisation at each fraction, however longer fraction times cause intra-fraction motion to become the dominant uncertainty. This study investigates whether bladder volume can predict intra-fractional CTV movement. Material/Methods: Ten patients with cervical cancer received weekly 1.5T MR scans during radiotherapy. As part of these scans, intra fraction movement was assessed by acquiring five axial and coronal T2-weighted MR scans at 2-minute intervals, emulating a 15-minute treatment window. Soft tissue rigid registration of the CTV using a clip-box around the contoured CTV was achieved via in-house software, estimating CTV motion using the initial MR scan as reference.

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