S160
Brachytherapy - Urology
ESTRO 2026
effectively balance constraints, enabling the simultaneous satisfaction of all requirements, unlike single-objective functions. Keywords: multi-objective optimization, low-dose-rate
normal tissue sparing. Adjusting these weights guided the genetic algorithm toward solutions that satisfied the prescribed dose objectives. The dose–volume constraints, based on AAPM recommendations, required that the dose covering 90% of the CTV (D90) exceed 100 Gy, and that no more than 50% of the CTV receive 150% or more of the prescribed dose (V150 ≤ 50%). Results: For SO-SPO, 10 iterations with four different weight settings generated 40 plans, none of which satisfied all clinical dose constraints. In contrast, MO-SPO produced 755 Pareto front solutions, providing a broader range of feasible plans, including six that met all constraints, as shown in Figure 1.
Digital Poster 1367
Severe late GU and GI adverse events following focal prostate salvage brachytherapy after single implantation and three fractions Bradley Pieters 1,2 , Colette van den Broek 1 , Katharina Brück 1 , Niels den Haan 1 , Boris Jansen 1 , Jan Wiersma 1,2 , Karel Hinnen 1 1 Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 2 Cancer Center Amsterdam, Cancer Treatment and Quality of Life, Amsterdam, Netherlands
Purpose/Objective: Salvage prostate brachytherapy (SPBT) for
radiorecurrent disease is evolving rapidly. A common approach is the administration of two to six fractions, implemented through multiple implantations. The undertaking of multiple implantations can pose challenges when access to the operating room is limited and may be perceived as inconvenient.In our institute, a three-fraction scheme within 24 hours is employed in a single implantation. The objective of this investigation was to determine whether the fractionation scheme, results in an increase in adverse events (AE). Material/Methods: From 2015-2023, 42 patients were treated with focal SPBT. The recurrent tumor was treated with a margin of 5-mm (CTV) following diagnostics that incorporated mpMRI, choline- and PSMA-PET, and whole-gland biopsies (Table1).
DVH analysis indicated that MO-SPO achieved more balanced and stable performance across CTV D90, CTV V150, and rectum D2cc, whereas SO-SPO exhibited higher urethral doses and greater variability. Further comparison with a clinical LDRBT plan revealed that both SO-SPO and MO-SPO produced localized high- dose regions due to the lack of explicit high-dose constraints; however, MO-SPO achieved superior target coverage (D90 = 100.8 Gy) and better rectal sparing (D2cc = 72.9 Gy) compared with SO-SPO (95.8 Gy, 78.7 Gy) and the clinical plan (111.4 Gy, 96.5 Gy), while all plans remained within urethral dose limits, as shown in Figure 2.
Conclusion: This study developed a direct optimization method for LDRBT seed distribution DVI based on NSGA-II and discussed the advantages of multi-objective functions over single-objective functions in solving LDRBT seed distribution optimization problems. Multi-objective functions can yield multiple feasible solutions and
Following the implantation, treatment was
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