ESTRO 2025 - Abstract Book

S4424

Late-breaking abstracts

ESTRO 2025

frequent in the radiotherapy arm (88% S1-S3, 11% S4-S5) vs. the surgical arm (38% S1-S3, 62% S4-S5). Median FU was 36 Months (38 for RT, 33 for surgery). R0 margins were achieved in 67% following surgery. 6 operated patients received post op RT. Among patients treated with definitive RT, 90% received carbon-ions, 10% received protons. There was no statistically significant difference in disease free survival among the 2 arms and this held true after stratifying for the anatomic level (see figure 1)

3Y-DFS was 73% for RT and 65% for surgery. 3Y-rates of distant metastasis were 13% for RT and 10% for surgery. 3Y-OS was 91% (RT) and 96% (surgery). In the RT arm severe toxicity rates were G3 22%, G4 0%, G5 0%. Corresponding rates were G3 10%, G4 7%, G5 1% after surgery. QOL analysis will be presented. Conclusion Trial accrual rate exceeded expectations. No patient could be enrolled to randomization. The interim analysis does not reveal any significant difference in recurrence and survival rates between wide en-bloc surgical resection or definitive RT. Present data suggest non-inferiority of conservative, function-sparing, high-dose particle therapy.

Keywords: sacral chordoma, particle therapy, Bayesian trial

References 1] Imai R, Kamada T, Araki N; Working Group for Bone and Soft Tissue Sarcomas. Carbon Ion Radiation Therapy for Unresectable Sacral Chordoma: An Analysis of 188 Cases. Int J Radiat Oncol Biol Phys. 2016 May 1;95(1):322 327. doi: 10.1016/j.ijrobp.2016.02.012. Epub 2016 Feb 8. PMID: 27084649.

5012

Proffered Paper First-in-world demonstration of benefit of AI assisted head and neck cancer target contouring in a prospective blinded randomized clinical trial Stine S Korreman 1,2 , Jintao Ren 1,2 , Jasper A Nijkamp 1,2 , Anne IS Holm 3 , Kristoffer Moos 1,2 , Kim M Hochreuter 1 , Hanne Primdahl 3 , Nicolaj Andreassen 3 , Kasper Toustrup 3 , Line MH Schack 3 , Jesper G Eriksen 4 , Mathis E Rasmussen 1,4 1 Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 3 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. 4 Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective This prospective randomized clinical trial aimed to demonstrate that the quality of AI-assisted GTV contouring in head and neck cancer is on par with manual contouring, through review and approval by a blinded multidisciplinary expert panel.