ESTRO 2025 - Abstract Book

S1905

Clinical - Urology

ESTRO 2025

References: [1] Buyyounouski MK, Pugh SL, Chen RC, Mann MJ, Kudchadker RJ, Konski AA, et al. Noninferiority of Hypofractionated vs Conventional Postprostatectomy Radiotherapy for Genitourinary and Gastrointestinal Symptoms: The NRG-GU003 Phase 3 Randomized Clinical Trial. JAMA Oncol. 2024;10:584-91. [2] Dubinsky P, Vojtek V, Belanova K, Janickova N, Balazova N, Tomkova Z. Hypofractionated Post-Prostatectomy Radiotherapy in 16 Fractions: A Single-Institution Outcome. Life (Basel). 2023;13. [3] Keall PJ, Brighi C, Glide-Hurst C, Liney G, Liu PZY, Lydiard S, et al. Integrated MRI-guided radiotherapy - opportunities and challenges. Nat Rev Clin Oncol. 2022;19:458-70.

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Poster Discussion Acute toxicity with SBRT vs fractionated IMRT to the prostate and pelvis in high-risk prostate cancer (SRAM): A randomized phase II study NCT03938649 Darren MC Poon 1,2 , Kenneth Wong 1 , Daisy Lam 1 , David Johnson 1 , Landon Chan 1 , CM Chu 3 , CF Ng 4 , Frankie Mo 1 , Tony Mok 1 1 Department of Clinical Oncology, The Chinese University of Hong Kong, Hong Kong, Hong Kong. 2 Comprehensive Oncology Center, The Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong. 3 Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Hong Kong, Hong Kong. 4 Department of Surgery, The Chinese University of Hong Kong, Hong Kong, Hong Kong Purpose/Objective: While fractionated intensity-modulated radiotherapy (IMRT) to the pelvis in addition to prostate-only RT improves clinical outcomes in high-risk prostate cancer (HR-PC) 1 , the safety and efficacy of stereotactic body RT (SBRT) in treating both the prostate and pelvis remain undetermined 2-3 . We reported the acute toxicity of SBRT and IMRT to the prostate and pelvis in localized HR-PC patients from a prospective randomized trial (ClinicalTrials.gov: NCT03938649). Material/Methods: SRAM is a phase II, open-label, randomized study conducted in a tertiary cancer institution. Men with node-negative HR-PC (T3 –T4 disease and/or PSA > 20 ng/mL and/or Gleason score [GS] ≥ 8) were randomly assigned (in a 1:1 ratio) to receive SBRT (prostate/pelvis: 40 Gy/25 Gy in 5 weekly-fractions) or IMRT (phase I pelvis: 50 Gy/25 fractions; phase II prostate: 26 Gy/13 fractions, over 7 – 8 weeks). Androgen deprivation therapy was started 3 – 4 months pre RT and continued for 18 – 24 months post-RT. Both arms received RT delivered by RapidArc ™ with daily image guidance using fiducial markers and on-board cone beam computed tomography. Rectal spacer was not used. The primary endpoint was the worst acute grade ≥ 2 (as per CTCAE) gastrointestinal (GI) and genitourinary (GU) toxicities up to 12 weeks post-RT. Key secondary endpoints included late toxicities, biochemical control, and survival. Results: From May 2019 to April 2024, 121 patients (median age, 72 years; Table) were randomly assigned to receive SBRT (N=60) or IMRT (N=61). Overall, 69.4% of patients had GS ≥ 8, 57.9% had staging PSMA -PET scans, and 100% completed the RT. No grade 3 acute toxicities were observed. Worst acute grade ≥ 2 GU toxicities were observed in 23.3% and 36.1% of patients with SBRT and IMRT, respectively ( p =0.1256). The SBRT group reported significantly fewer acute grade ≥ 2 GI toxicities than the IMRT group (1.7% vs 23.0%; p =0.0003). Diarrhea was the most common acute grade ≥ 2 GI toxicity in both groups (SBRT, 6.45% vs IMRT, 21%; p =00086).