ESTRO 2025 - Abstract Book

S1531

Clinical – Mixed sites & palliation

ESTRO 2025

(range 3.2-77.3). Cumulative LF incidence was 15.5% at 1 year (95% CI:10-21%) and 23.7% at 2 years (95% CI:17-31%). A trend towards reduced LF was observed with CTV-margins utilisation, but without statistical significance (p=0.32; see Figure 2), even after adjusting for confounders (p=0.13). LF patterns with and without CTV-margins were distributed as 23.1% and 27.8% in-field, and 76.9% and 72.2% margin/out-of-field, respectively (p=0.73). LF was potentially preventable in 0%, 7.7%, and 27.7% of the recurrences with hypothetical CTV-margins of 5, 10 and 20 mm, respectively (p<0.001). On multivariable analysis, larger GTV size (p=0.04) and induced oligoprogressive disease (p=0.02) were associated with an increased LF risk, whereas non-pelvic location (p=0.04) and a prescription dose of 27Gy/3 fractions (p<0.001) were protective.

Conclusion: The use of a CTV-margin did not significantly reduce LF rate. However, a CTV-margin was applied in only a quarter of cases, likely limiting the study’s power, and its size was variable. This preliminary analysis will be expanded with additional patients to refine the failure patterns and explore the necessity and optimal size of CTV-margins to effectively treating microscopic disease and preventing intra-osseous dissemination.

Keywords: Bone metastases, SBRT, oligometastases

References: Chen X, LeCompte MC, Gui C, Huang E, Khan MA, Hu C, et al. Deviation from consensus contouring guidelines predicts inferior local control after spine stereotactic body radiotherapy. Radiotherapy and Oncology. 2022;173:215-22. De la Pinta C. SBRT in non-spine bone metastases: a literature review. Med Oncol. 2020;37(12):1-7. Moore-Palhares D, Zeng KL, Tseng CL, Chen H, Myrehaug S, Soliman H, et al. Stereotactic Body Radiation Therapy for Sacral Metastases: Deviation From Recommended Target Volume Delineation Increases the Risk of Local Failure. International Journal of Radiation Oncology*Biology*Physics. 2024;119(4):1110-21.

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Digital Poster Body composition is associated with worse clinician- and patient-reported late radiotherapy-related toxicity in the REQUITE study. Alexander J Vickers 1,2 , Donal M McSweeney 3,2 , Ananya Choudhury 1,2 , Jamie Weaver 4,2 , Gareth Price 3,2 , Alan McWilliam 3,2 1 Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 2 . Division of Cancer Sciences, School of Medical Sciences, Faculty of Biology, Medicine & Health, University of Manchesrer, Manchester, United