S159
Brachytherapy - Urology
ESTRO 2026
Purpose/Objective: Updated results are presented on oncological outcomes including ADT-free survival and toxicity in a prospective cohort of 231 patients treated with focal salvage HDR brachytherapy for locally recurrent prostate cancer after primary radiotherapy. Material/Methods: Patients treated with focal salvage HDR brachytherapy for iT2a-3bN0M0 locally recurrent prostate cancer between July 2013 and October 2023 in two Dutch radiotherapy facilities after primary radiotherapy were prospectively followed. Patients with previous salvage treatment were excluded. Biopsies of the recurrent disease were not mandatory. The HDR brachytherapy catheters were transperineally placed within the local recurrence in the prostate and/or seminal vesicle, through TRUS/MR- or TRUS/CT image guidance. The target volume was defined based on PSMA PET-CT and multiparametric MRI (mp-MRI) imaging. Treatment consisted of one fraction of 19 Gy to the tumor.Oncologic outcomes were biochemical disease- free survival (bDFS), local recurrence-free survival (LRFS), metastases-free survival (MFS) (either lymph node- or distant metastases), ADT-free survival (ADTFS) and overall survival (OS). Side effects were measured using the Common Terminology Criteria for Adverse Events (CTCAE) 4.0 and patient-reported outcome measures (PROMs). Results: A total of 231 patients were analysed. Three-years estimates for bDFS, LRFS, MFS, ADTFS and OS were 52% (95%CI 44-59 %), 58% (51%-65%), 81% (75%-87%), 88% (83%-92%) and 96% (93%-98%) respectively. Kaplan-Meier plots are shown in Figure 1. New grade ≥ 2 acute gastrointestinal (GI) and genitourinary (GU) toxicity was present in 1.4% and 14.4% of patients, while grade ≥ 2 late GI and GU toxicity was present in 8.4% and 40.0%. Most of the latter consisted of grade 2 toxicity due to the use of medication for obstructive and -urinary urgency complaints. One patient (0.4%) experienced grade 4 GU toxicity with prostate necrosis and urosepsis followed by cystoprostatectomy and seven (3.0%) had grade 3 GU toxicity. There was no grade 4 GI toxicity and one case (0.4%) of grade 3 GI toxicity. New late erectile dysfunction grade ≥ 2 was present in 45.4%. Patient-reported quality of life remained relatively stable over time with a minor increase in International Prostate Symptom Score (IPSS) and decrease in International Index of Erectile Function (IIEF) scores.
Conclusion: With a three-years bDFS of 52% and a three-years ADT-free survival of 88%, focal salvage HDR brachytherapy is a valid treatment option for selected patients to delay disease progression and deter ADT in locally recurrent prostate cancer after radiotherapy. Toxicity was predominantly manageable, with ≥ grade 3 events being rare. Keywords: Recurrence, Focal salvage, Toxicity A Multi-Objective Optimization Framework for Personalized Seed Distribution Planning in Prostate Low-Dose-Rate Brachytherapy Binbing Wang Radiation Physics, Zhejiang Cancer Hospital, Hangzhou, China Purpose/Objective: The research aimed to explore the advantages of voxel-based multi-objective optimization over single- objective (SO-SPO) optimization in addressing seed distribution issues in prostate cancer LDR treatment. Material/Methods: Digital Poster 1326 A multi-objective non-dominated genetic algorithm (NSGA-II) was developed to optimize seed implantation positions in prostate brachytherapy. The optimization directly targeted dose–volume indices (DVIs) while incorporating inverse planning to refine implantation control parameters. The proposed algorithm was evaluated using a large prostate cancer case with 335 candidate dwell positions, addressing an optimization problem involving 80 variables and four clinical constraints through the multi-objective seed position optimization method (MO-SPO). In the single-objective optimization (SO-SPO) approach, the fitness of each individual was defined as a weighted sum of the CTV and OAR fitness values, with hyperparameters controlling the trade-off between tumor coverage and
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