ESTRO 2025 - Abstract Book

S1819

Clinical – Upper GI

ESTRO 2025

Conclusion: PTV volumes are reduced with AC. However, there is minimal difference to OAR dose; lower heart and stomach doses are marginal and unlikely to be of clinical significance. This may be due to the effect of AC on OAR shape, for example, the mitigation of inspiration reducing overall lung volume. Further work is being undertaken to assess if AC confers benefit by improving plan robustness. A limitation is that this was a retrospective audit. As no 3DCT reference scans were obtained in free-breathing, mid ventilation phase of the 4D scan were used as the ‘reference’ volume for this study, which is not a reflection current practice in our centre. Additionally, no patient reported outcome measures were recorded. The benefit of AC remains uncertain in photon-based OG RT. For some patients, e.g. with substantial respiratory motion, the additional burden of using AC may be justified but the appropriate selection criteria is yet to be clearly defined. References: 1. Daly, M., McWilliam, A., Radhakrishna, G., Choudhury, A., & Eccles, C. L. (2022). Radiotherapy respiratory motion management in hepatobiliary and pancreatic malignancies: a systematic review of patient factors influencing effectiveness of motion reduction with abdominal compression. Acta Oncologica , 61 (7), 833–841. https://doi.org/10.1080/0284186X.2022.2073186 2. SCOPE 2 Protocol. https://www.thelancet.com/cms/10.1016/j.eclinm.2023.102059/attachment/ce598af2-3843 4ff9-a07c-378e7592d1b0/mmc2.pdf Keywords: Motion management, dosimetry