ESTRO 2025 - Abstract Book

S1817

Clinical – Upper GI

ESTRO 2025

3154

Digital Poster Assesing the dosimetric impact of abdominal compression use in distal oesophago-gastric cancer radiotherapy. Nicholas A Gomez 1 , Dafydd P Roberts 2,3 , Sarah Gwynne 1,3 , Adam Selby 2 , Filippos Apostolopoulos 2 , Owen Nicholas 1,3 1 Oncology, South West Wales Cancer Centre, Swansea, United Kingdom. 2 Medical Physics, South West Wales Cancer Centre, Swansea, United Kingdom. 3 Faculty of Medicine, Health and Life Science, Swansea University, Swansea, United Kingdom Purpose/Objective: Distal oesophago-gastric (OG) tumours are susceptible to respiratory motion due to its proximity to the diaphragm. Abdominal compression (AC) belts are commonly used to mitigate respiratory motion in abdominal radiotherapy. By reducing motion, it is postulated that AC reduces organ-at-risk(OAR) dose and improves target volume(TV) coverage. A systematic review by Daly et al. (2022) of patients with hepatobiliary cancers, showed that AC reduced craniocaudal respiratory motion for majority of patients, however, there were four studies which demonstrated increases in at least one direction. However, there is little published data about advantages of AC in OG radiotherapy. This study investigates dosimetric impact of AC use in OG cancers. Material/Methods: Five patients either distal or gastro-oesophageal junction cancers with 4DCT in free-breathing and with AC were identified. Delineation and planning constraints followed SCOPE2 trial protocol. TV and OAR were delineated on 4DCT scans on free-breathing (FB) and AC scans (see Figure 2). Auto-contouring was used for OAR volumes. All volumes were finalised by a clinical oncologist. Photon treatment plans for both sets of volumes were optimised on mid ventilation phase using constraints. DVH metrics including TV coverage, lung, heart, liver and stomach dose were reported. Results: Five pairs of plans were created. On average there was a 10% ( ± 2% SE) reduction in PTV volume with use of compression belt. As shown in Figure 1, mean doses to the stomach and heart were marginally lower with AC. Lung, liver and spleen mean doses were marginally higher with AC.