S1154
Clinical - Urology
ESTRO 2026
a median decrease of 4 (IQR, -6-0) at two-years. At one- and two-years there was a median decrease in SHIM score of 1 (IQR, -4.5-0.5) and 1 (IQR, -6.5-0.5), respectively. Rates of grades 1/2 urinary toxicity at one- and two-years were 30%/20% and 5%/15%, while rates of grades 1/2 bowel toxicity were 0%/10% and 5%/5%, respectively. Median decrease in PSA at one- and two-years was 81.3% (IQR, 71%-89%) and 94.8% (IQR, 88.7%-95.9%). Conclusion: Two-fraction prostate SABR using peri-rectal spacing appears to be safe with acceptable long-term toxicity and excellent PSA response. The randomized SABR- Dual trial is ongoing. Keywords: Prostate, 2-fraction, SABR interfractional HyperSight TM -CBCT radiomics in adaptive ultra- and moderate hypofractionated prostate RT Alicia S. Bicu 1,2 , Natalie Abel 1 , Ralf Schmidt 1,2 , Victor Siefert 1,2 , Miriam Eckl 1 , Florian Stieler 1,3 , Marvin Willam 1 , Matthias Froelich 4 , Stefan O. Schoenberg 4 , Michael Ehmann 1,2 , Daniel Buergy 1,2 , Jens Fleckenstein 1 , Frank A. Giordano 1,2 , Judit Boda- Heggemann 1,2 , Constantin Dreher 1,2 1 Department of Radiation Oncology, University Medical Centre Mannheim, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany. 2 DKFZ- Digital Poster 825 Impact of biologically effective dose on Hector Cancer Institute, University Medical Centre Mannheim, Mannheim, Germany. 3 Junior Research Group “Image and Surface guided Radiotherapy”, Mannheim Institute for Intelligent Systems in Medicine (MIiSM), University of Heidelberg, Mannheim, Germany. 4 Department of Radiology and Nuclear Medicine, University Medical Centre Mannheim, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany Purpose/Objective: To quantify the relationship between accumulated biologically effective dose (BED) and interfraction percentage changes in radiomic features based on advanced, HU stable fractional CBCT imaging during radiotherapy for prostate cancer with different fractional courses, and to identify the most dose- responsive radiomic features. Material/Methods: Twenty patients with localized prostate cancer, 10 treated with adaptive ultrahypofractionated RT (UHFX, 40 Gy in 5 fractions) and 10 with moderate hypofractionation (MHFX) 60 Gy in 20 fractions) on an HyperSight™ CBCT equipped Ethos™ linear accelerator (Varian, Siemens Healthineers) were
evaluating SF-SABR for patients with larger, stage T1b- 2a, primary kidney cancers. Though follow up is still relatively limited, SF-SABR demonstrated excellent tumor control and was well tolerated. Keywords: Kidney, SABR
Mini-Oral 804
Long-term toxicity and PSA dynamics in the initial cohort of SABR-Dual: Two-fraction stereotactic radiotherapy for localized prostate (NCT06027892) Elisha Fredman 1 , Mirona Attrash 1 , Eyal Yosefof 1 , Assaf Moore 1,2 , Roi Tschernichovsky 1,3 , Dimitri Bragilovski 1 , Miriam Weinstock-Sabbah 1 , Jonathan Kindler 1 , Ruth Dadush Azuz 1 , Roman Radus 1 , Oded Icht 1,4 , Shay Golan 5 , Tzippora Shochet 6 , Dror Limon 1 1 Radiation Oncology, Davidoff Cancer Center, Petah Tikvah, Israel. 2 Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA. 3 Molecular and Cell Biology, Weizmann Institute of Science, Rehovot, Israel. 4 Radiation Oncology, Princess Margaret Cancer Centre, Toronto, Canada. 5 Urology, Rabin Medical Center, Petah Tikvah, Israel. 6 Biostatistics, Beilinson Hospital, Petah Tikvah, Israel Purpose/Objective: SABR-Dual is a phase-III trial of two-fraction stereotactic radiotherapy (SABR) with optional MRI- based boost, using peri-rectal spacing, for localized prostate cancer. Herein we present long-term (two- year) toxicity and PSA response dynamics from the initial phase-I safety cohort. Material/Methods: 20 patients with favorable intermediate-risk prostate adenocarcinoma received a dose of 27 Gy in two fractions, with an optional integrated boost (SIB) to 30 Gy. All underwent radiopaque hydrogel spacer and fiducial marker placement. MRI-based treatment planning and CT-based image guidance with live fiducial tracking was applied. The primary endpoint of this analysis is one- and two-year patient-reported quality of life based on EPIC-26, IPSS, and SHIM questionnaires. Secondary endpoints include patient reported toxicity (using CTCAEv5) and temporal PSA dynamics. Results: Median prostate volume was 44cc (IQR, 29.5-56), and 50% received an SIB. Median baseline IPSS was 8.1 (IQR, 4.5-11). In the EPIC-26 domains of urinary incontinence, obstruction, bowel, sexual, and hormonal symptoms, a minimally clinically important change occurred at one-year in 4/20 (20%), 6/20 (30%), 6/20 (30%), 8/20 (40%), and 3/20 (15%), improving by two-years to 1/20 (5%), 1/20 (5%), 1/20 (5%), 7/20 (35%), and 0/20 (0%), respectively. A median increase in IPSS of 1 (IQR, -1.5-6) was reported at one-year, with
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