S1261
Clinical - Urology
ESTRO 2026
Front Oncol. 2022;12:837790. doi:10.3389/fonc.2022.837790 Keywords: Reirradiation, MR-guided SBRT, biochemical control
generation imaging (NGI) techniques enable early and precise detection of recurrences. MR-guided stereotactic ablative body radiotherapy (SBRT) is a promising and safe option due to its precise treatment adaptation and reduced adverse events. This study aims to evaluate side effects and biochemical control in patients treated with MR-guided SBRT for macroscopic local recurrence. Material/Methods: Nine patients with macroscopic local recurrence confirmed by NGI, previously treated with RP and/or radiotherapy (RT), were analyzed. Patients were treated with MR-guided SBRT, receiving doses of 35–36 Gy in 5 fractions every other day with daily volume adaptation. The use of adjuvant androgen deprivation therapy (ADT) was allowed in patients with high-risk factors. Acute and late side effects were assessed using CTCAE v5.0, and biochemical control was reported (PSA ≥ 0.2 ng/mL above the nadir or PSA nadir + 2 ng/mL (Phoenix criterion)). Results: The median time from initial RT (two LDR-BT, two EBRT, five RP + EBRT) to reirradiation was 84 months (range 18–252). Seven patients also received concurrent or adjuvant ADT. The median PSA at relapse was 2.25 ng/mL (range 0.64–6.98 ng/mL).With a median follow-up of 13 months, all patients completed treatment without interruptions. Genitourinary (GU) side effects were mild: four patients experienced G1, predominantly urinary incontinence and urgency, and one patient experienced G2 side effects, consisting of a urinary stricture; four patients reported no adverse events. No gastrointestinal (GI) side effects were observed. Biochemical control at 6 and 12 months was 100%, with a mean PSA at 6 and 12 months of 0.05 ng/mL and 0.04 ng/mL, respectively. Conclusion: MR-guided SBRT for macroscopic local recurrence after RP and RT is safe, feasible, and well-tolerated, with promising preliminary biochemical control outcomes. NGI for patient selection, the interval from prior RT, and ADT use are key factors in treatment planning and outcomes. Further studies are warranted. References: Alongi F, Fiorentino A, Livi L, et al. Stereotactic MR- guided adaptive radiotherapy for localized recurrent prostate cancer after radical prostatectomy or radiotherapy. Radiother Oncol. 2021;159:194–201. doi:10.1016/j.radonc.2021.06.006Bruynzeel AME, Tetar SU, Oei SS, et al. Clinical outcomes of reirradiation for prostate cancer using MR-guided adaptive SBRT. Int J Radiat Oncol Biol Phys. 2021;110(2):398–409. doi:10.1016/j.ijrobp.2020.11.032D’Agostino G, Alongi F, Lancia A, et al. Stereotactic body re-irradiation for locally recurrent prostate cancer: a systematic review.
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Baseline IPSS and Planning Target Volume as Independent Predictors of Urinary Toxicity in RayPilot-Guided SBRT for Prostate Cancer. Melpomeni Kountouri, Giorgio Lamanna, Fréderic Miéville, Philippe Jungo, Damien Fuligno, Abdelkarim Said Allal Department of Radiation Oncology, HFR Fribourg, Fribourg, Switzerland Purpose/Objective: Pretreatment urinary symptom severity, assessed via the International Prostate Symptom Score (IPSS), and tumor burden, reflected by planning target volume (PTV) boost size, are established predictors of genitourinary (GU) toxicity in prostate stereotactic body radiotherapy (SBRT). While IPSS guides patient selection, its prognostic value in hypofractionated regimens like RayPilot-guided SBRT—featuring real- time intrafractional tracking—remains underexplored. Larger PTV volumes correlate with higher toxicity risks due to increased urethral/bladder exposure. This study evaluates IPSS and PTV boost as independent predictors of acute and late GU toxicity in a RayPilot- SBRT cohort, using updated dosimetric and clinical data to inform risk stratification. Material/Methods: We retrospectively analyzed 26 consecutive patients with localized prostate cancer treated with RayPilot® - guided SBRT between June 2024 and August 2025. The prostate and seminal vesicle bed were treated to 32.5 Gy with a simultaneous integrated boost of 36.25 Gy to the prostate over 5 daily fractions. Baseline IPSS and PTV boost volumes were correlated with acute/late grade ≥ 2 (G2+) GU toxicity via Pearson/point-biserial correlations and partial correlations (adjusting for IPSS or PTV). Results: In total 26 patients were included with a median age of 71 years (IQR 62.9-74.4); Gleason score 6 (15.4%) and 7 (84.6%) and a median baseline PSA 6.0 ng/mL (IQR 5.0- 7.0. Nineteen (73.1%) patients received ADT. The median IPSS was 5.0 (IQR 2.0-9.0; mild 61.5% [16/26], moderate 34.6% [9/26], severe 3.8% [1/26]. The median PTV boost was 104.7 cc (range 51.7-165.3 cc). Median follow-up was 5.9 months (IQR 3.21- 7.77).Acute G2+ GU toxicity occurred in 76.9% (20/26), G2 being the maximum acute and late toxicity reported at last follow up, primarily of irritative symptoms, relieved with NSAIDs. Late G2+ GU toxicity
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