ESTRO 2025 - Abstract Book

S3164

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

3136

Digital Poster Geometrical uncertainties in rectal cancer radiotherapy: a systematic literature review Giovanna Mantello 1 , Elena Galofaro 1 , Cihan Gani 2 , Daniel Portik 3 , Lynsey Devlin 4,5 , Robin De Roover 6 , Rianne M A J de Jong 7 , Ane Appelt 8 1 Radiotherapy Department, Azienda Ospedaliero Universitaria delle Marche, Ancona, Italy. 2 Department of Radiation Oncology, University Hospital and Medical Faculty Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany. 3 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands. 4 Department of Radiotherapy, The Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 5 CRUK RadNet Glasgow, University of Glasgow, Glasgow, United Kingdom. 6 Department of Radiation Oncology, University Hospitals Leuven, Leuven, Belgium. 7 Department of Radiation Oncology, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands. 8 Leeds Institute of Medical Research at St James's, University of Leeds, Leeds, United Kingdom Purpose/Objective: This systematic literature review aimed to evaluate the treatment uncertainties associated with modern rectal cancer radiotherapy, focusing on systematic and random errors in setup and target volume shape variation. It was conducted in support of an ESTRO guideline on the technical aspects of rectal cancer radiotherapy. Material/Methods: A systematic literature search was conducted to identify relevant studies, including all papers reporting on uncertainties in rectal cancer or general pelvic radiotherapy delivery and their relationship with general parameters (RT schedule, patient position, body mass index) and pelvic regions (bone, Gross Tumour Volume (GTV T, GTV N), rectum, mesorectum and pelvic elective lymph nodes); non-English language publications were excluded. Results: 2137 reports were identified, 196 were assessed for full-text screening, and 32 publications were selected for final reporting. Most authors utilized bunker-acquired imaging to calculate setup errors and target volume shape variations, reporting substantial uncertainties. GTV-T, GTV-N, CTV mesorectum, and elective lymph nodes were studied separately. Setup errors were analyzed in 12 studies using image-guided radiotherapy (IGRT). Differences were noted between prone and supine patient positions, with prone positions often yielding higher error rates, particularly when a belly board was used. Nine studies focused on rectal and mesorectal motion, the majority revealing asymmetric random (σ) and systematic (Σ) target shape variation. The anterior surface of the mesorectum demonstrates greater movement in the upper half compared to the lower half. Conversely, the posterior surface shows greater movement in its lower half. Twelve studies investigated the interfractional shape and position variation of tumour volume (GTV T, GTV N) and found significant random (σ) and systematic (Σ) errors that were more consistent in the cranio-caudal (CC) and antero-posterior (AP) directions. Selected publications analysed the positional uncertainties of elective draining lymph nodes, which are typically not removed during surgery, showing their small positional variations in relation to bone structures. Conclusion: Setup and target volume shape variations are significant and non-negligible geometric uncertainties that remain important even with the use of modern radiotherapy planning and delivery techniques in the treatment of rectal cancer. Setup errors can be easily minimized with daily IGRT alignment to bony structures; however, residual rotational errors may persist. Target volume shape variations are more challenging to correct, particularly for the mesorectum, where the variations are large, complex, and independent of bony landmarks.

Keywords: UNCERTAINTIES, RECTAL CANCER, SYSTEMATIC REVIEW