S885
Clinical - Mixed sites & palliation
ESTRO 2026
2642 COMPARISON OF TARGET VOLUME DEFINITION CONCEPTS IN SBRT FOR VERTEBRAL METASTASES: A SECONDARY ANALYSIS OF TWO PROSPECTIVE CLINICAL TRIALS Matthias Guckenberger 1 , Indira Madani 1 , Reinhart A. Sweeney 2 , Maria Hawkins 3 , Jose Belderbos 4 , Nicolaus Andratschke 1 , Merina Ahmed 5 , Frederick Mantel 6 , Flentje Michael 6 , Charlotte Billiet 7 , Susanne Rogers 8 , Ciro Franzese 9 , Daniel Schnell 10 , Mateusz Spa ł ek 11 , Daniel M. Aebersold 12 , Hossein Hemmatazad 12 , Thomas Zilli 13 , Judit Boda-Heggemann 14 , Brigitta G. Baumert 15 , Jean-Jacques Stelmes 16 , Franziska Nägler 17 , Philipp Gut 18 , Christian Weiß 19 , Alessio Bruni 20 , Robert Förster 21 1 Radiation Oncology, University Hospital Zurich, Zurich, Switzerland. 2 Radiation Oncology, Leopoldina Hospital Schweinfurt, Schweinfurt, Germany. 3 Medical Physics & Biomedical Engineering, University College London, London, United Kingdom. 4 Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, Netherlands. 5 Radiotherapy, Royal Marsden NHS Foundation Trust, London, United Kingdom. 6 Radiation Oncology, University Hospital Würzburg, Würzburg, Germany. 7 Radiation Oncology, Iridium Netwerk, Antwerp, Belgium. 8 Radio-Onkologie- Zentrum Mittelland, Kantonsspital Aarau, Aarau, Switzerland. 9 Radiotherapy and Radiosurgery, Humanitas Research Hospital IRCCS, Milan, Italy. 10 Radiation Oncology, University Hospital Freiburg, Freiburg, Germany. 11 Radiotherapy, Maria Sklodowska- Curie National Research Institute of Oncology, Warsaw, Poland. 12 Radiation Oncology, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland. 13 Radiation Oncology, Oncology Institute of Southern Switzerland, EOC, Bellinzona, Switzerland. 14 Radiation Oncology, University Medical Center Mannheim, Mannheim, Germany. 15 Radiation Oncology, Kantonsspital Graubunden, Chur, Switzerland. 16 Health Directorate, Luxemburg Health Directorate, Luxemburg, Luxembourg. 17 Radiotherapy, University Hospital Leipzig, Leipzig, Germany. 18 Radiotherapy, Hirslanden Clinic, Zurich, Switzerland. 19 Department of Radiotherapy and Oncology, Darmstadt General Hospital, Darmstadt, Germany. 20 Department of Oncology and Hematology, University Hospital of Modena, Modena, Italy. 21 Radiation Oncology, Kantonsspital Winterthur, Winterthur, Switzerland Purpose/Objective: To compare treatment outcome of GTV-based and a segment-based target volume definition concepts in SBRT for vertebral metastases. Material/Methods:
This is a secondary analysis of two prospective clinical trials (clinicaltrials.gov NCT01594892 [DOSIS1] conducted between 2012 and 2015 and NCT02800551 [DOSIS2] conducted between 2016 and 2023), both enrolled patients who were treated with SBRT for painful mechanically stable or potentially unstable vertebral metastases. In both trials SBRT delivered two dose levels using simultaneous integrated boost: 35- 40 Gy/5 or 48.5 Gy/10 to the high-dose planning target volume (PTV) and 20 Gy/5 and 30 Gy/10 to the conventional-dose PTV, respectively. In the DOSIS1 trial the high-dose PTV was created around the CT and/or MRI-based gross tumor volume (GTV) to encompass all vertebral elements at the risk of recurrence - body, pedicles, transverse process, and spinous process - of the involved vertebra minus the spinal cord planning-at-risk volume (PRV) [1]. In the DOSIS2 trial the high-dose PTV resulted from a 2-mm isotropic expansion of the CT and/or MRI-based GTV minus the spinal cord PRV. The conventional-dose PTV was identical in both groups and included the uninvolved parts of the affected vertebra. The endpoints of this analysis – freedom from local progression (FFLP) and vertebral compression fracture (VCF) estimated with the Kaplan-Meier method – were compared between the groups. Results: A total of 205 patients (57 with 63 metastases in DOSIS1 and 148 with 164 metastases in DOSIS2) were included in this analysis (Table 1). The high-dose PTV in DOSIS1 group was significantly larger than in DOSIS2 group (median 57.7 cm3 [IQR 34.1-99.1 cm3] vs median 10.3 cm3 [IQR 5-25.6 cm3], respectively, P<.001). After a median follow-up of 19 months (DOSIS1) and 22 months (DOSIS2), 90 patients (44%) died, and 11 patients (5%) had local failure. The 1- and 2-year FFLP rates were significantly lower in DOSIS1 vs DOSIS2 (87.8% vs. 98.3% % and 87.8% vs. 94.6%, respectively, P=.007). Of 224 metastases assessed radiologically during follow-up, there were 12 (20%) and 13 (7.9%) de novo VCFs in DOSIS1 and DOSIS2 group, respectively, resulting in significantly different 1- and 2-year de novo VCF rates of 17.7% vs. 7.5% and 22.6% vs. 10.8%, respectively (P=.01). No myelopathy or plexopathy were observed in either group.
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