S1053
Clinical – Sarcoma, skin cancer, malignant melanoma
ESTRO 2026
across online ART patients were 98.3% (±2.4%) in scheduled plans versus 99.9% (±0.09%) in adapted plans (p<0.001). Similarly, PTV V95% and D0.03cm ³ were significantly improved (p<0.001) in adapted plans vs scheduled plans, 97.6% (±0.5%) vs 96.3% (±2.2%) and 106.7% (±0.8%) vs 108.7% (±1.5%), respectively (Figure 1). Mean bowel D0.03cm ³ was also significantly lower with the adapted plan (1.97 Gy) vs the scheduled plan (2.06 Gy) (p<0.001). In the offline ART cohort, 3 of 6 patients required at least one CBCT-based replanning during their treatment course due to tumor swelling. All patients completed RT as prescribed, with no high-grade side effects during RT.
Digital Poster 4776
Early Clinical Experience with HyperSight CBCT- Based Adaptive Radiotherapy for Extremity and Abdominopelvic Soft Tissue Sarcomas Reinhardt Krcek 1,2 , Teuta Z. Mustafayev 1,3 , Michael Mcmahon 1,3 , Samuel Appiah 1,3 , Jean-Pierre Bissonnette 1,4 , Charles Catton 1,3 , Peter W. Chung 1,3 , Dana Keilty 1,3 , Vickie Kong 1,3 , David B. Shultz 1,3 , Teodor Stanescu 1,3 , Tony Tadic 1,3 , Michael Velec 1,3 , Jeff Winter 1,3 , Philip Wong 1,3 , Jan Seuntjens 1,4 , David G. Kirsch 1,3 , Monica Serban 1,3 1 Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 2 Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Zurich, Switzerland. 3 Department of Radiation Oncology, University of Toronto, Toronto, Canada. 4 Department of Medical Biophysics, University of Toronto, Toronto, Canada Purpose/Objective: To evaluate the feasibility and dosimetric benefit of implementing cone-beam computed tomography (CBCT)-based online and offline adaptive radiotherapy (ART) for soft tissue sarcomas (STS). Material/Methods: We conducted a retrospective review of patients with abdominopelvic and lower extremity STS treated at the Ethos (v2.0, Varian Medical Systems) system with HyperSight CBCT. For abdominopelvic targets, online ART was performed and the reference ART plan was compared to non-adaptive standard-of-care (SoC) plans generated in RayStation (V10B, RaySearch Laboratories) using 5-mm planning target volume (PTV) margins. The Ethos workflow generally maintained 5-mm PTV margins but incorporated an organ-at-risk (OAR)-guided clinical target volume (CTV) margin-reduction strategy by cropping the CTV away from OARs, and relaxed PTV objectives to maintain target coverage while minimizing OAR dose. Dose- volume statistics from SoC and Ethos scheduled and adapted plans were analyzed with descriptive statistics and Student’s t-tests. Extremity STS cases were managed with offline ART by re-planning directly on CBCT (turnaround time of 48 hours). Results: Ten patients (median age 66 years) were analyzed: four with abdominopelvic STS treated with online ART and six with extremity STS treated with offline ART. In the online ART cohort, Ethos ART reference plans allowed for smaller CTV and PTV volumes ( − 7% and − 9%) and achieved substantially lower bowel doses (V30Gy − 39%, V40Gy − 45%) compared with SoC plans (Table 1). The adapted plan was selected in 98 of 100 online ART sessions. The average on-couch adaptation time (CBCT to CBCT) was <24 minutes. Mean CTV V97%
Conclusion: We successfully implemented a streamlined Ethos- based adaptive workflow for STS. Online ART achieved highly reproducible target coverage and significant OAR dose reduction, outperforming SoC and scheduled plans. Offline ART offered a practical solution for extremity sarcomas, enabling rapid CBCT- based replanning. These findings support the feasibility and clinical value of integrating ART in routine sarcoma management. Keywords: Adaptation, High Resolution CBCT, Dosimetry Digital Poster 4802 Prognostic factors and long-term outcomes in patients with melanoma brain metastases treated with radiosurgery Enrico Pozzo 1 , Pierina Navarria 1 , Elena Clerici 1 , Federico Pessina 2,3 , Aurora Sasso 1 , Mariya Ilieva 1 , Davide Franceschini 1 , Giacomo Reggiori 1 , Stefano Tomatis 1 , Ciro Franzese 1,3 , Marta Scorsetti 1,3 1 Department of Radiotherapy and Radiosurgery, IRCCS Humanitas Research Hospital, Milan, Italy. 2 Department of Neurosurgery, IRCCS Humanitas
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