ESTRO 2025 - Abstract Book

S2041

Clinical - Urology

ESTRO 2025

Conclusion: Our results show that CIRT can be safely and effectively applied in patients with advanced prostate cancer, leading to low toxicity and high tumor control, even in patients with N+, and replicating Japanese data.

Keywords: Prostate cancer, Carbon ions, particle therapy

References: 1 Nomiya T et al. A multi-institutional analysis of prospective studies of carbon ion radiotherapy for prostate cancer: A report from the Japan Carbon ion Radiation Oncology Study Group (J-CROS). Radiother Oncol. 2016 Nov;121(2):288-293. doi: 10.1016/j.radonc.2016.10.009. Epub 2016 Nov 9. PMID: 27836119. 2 Clinical trials registration: NCT03049072

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Digital Poster Modelling of late genitourinary toxicity from re-irradiation of recurrent prostate carcinoma – results from a prospective study Sara Pilskog 1,2 , Sander Blørstad Thu 2 , Øyvind Lunde Rørtveit 1,2 , Helge Egil Seime Pettersen 1 , Liv Bolstad Hysing 1,2 , John Alfred Brennsæter 1 , Christian Ekanger 1 1 Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway. 2 Institute of Physics and Technology, University of Bergen, Bergen, Norway Purpose/Objective: Re-irradiation with complete overlap of irradiated volume is a treatment option for prostate patients with localised recurrences following previous radiotherapy. Improved knowledge of the cumulative dose tolerance for surrounding organs such as the bladder is needed to facilitate this treatment option. One challenge is to add doses despite anatomical changes that has occurred between the two treatments. This study aims to include motion modelling when assessing dose-response for prostate patients treated in a single centre re-irradiation study. Material/Methods: Patients received re-irradiation in 2013-2017 according to the study protocol and consented to enrolment. Inclusion criteria besides clinic-pathological indications included >2 years since primary radiation and no prevailing toxicity greater than RTOG grade 1. Hypofractionated radiotherapy of 7 Gy in 5 fractions, was delivered every other day. Image-guidance was used with intra-prostatic fiducial markers. Peak RTOG late genitourinary (GU) toxicity was scored. Cut-off logistic regression models for late GU toxicity were fit to the summed dose-volume histogram doses and to accumulated bladder doses. The cut-offs aimed to find the volume separating patients with and without toxicity and was defined as the lowest p-value using t-test and with 95% confidence levels estimated using leave one-out analysis. Dose accumulation used shrinkage estimation, a statistical method previously shown to reduce systematic errors from organ deformation and improve estimation of the organ mean shape [1]. Shrinkage estimation was used to form a likely mean bladder shape for each patient based on input from another prostate patient cohort and the two bladders available per patient in receiving re-irradiation. Receiving operating characteristics and the area under this curve (AUROC) was used to compare modelling results. Results: For 28 of the 39 study patients, both treatment plans were available. Of these, 9 patients reported GU toxicity grade ≥ 2, including 3 patients with GU toxicity of grade 3. The cut - offs for grade ≥ 2 were similar for both summed and accumulated doses (Figure) but differed for grade 3: D40% for summed doses and D5% for accumulated doses. The highest AUROC values were found with the logistic regression model with dose summation for grade ≥ 2 but with the dose accumulation model for grade 3 (Table).