S152
Brachytherapy - Urology
ESTRO 2026
A method to reduce the number of ordered seeds and the corresponding radioactive waste. Albert Bartrés Salido, Melanie Erzilbengoa, Verónica Alba, Pedro Liñán Rodríguez, Carlos Fernandez Leira, Marta Sanchez Casi, Nagore García Apellániz, Sergio Panzuela, Miren Lamaison Bidarte, Maddalen Alonso Etxarri, Francisco Jose Lozano Flores Medical Physics, Osakidetza, Donostia, Spain Purpose/Objective: In I-125 seed brachytherapy planning, one of the initial steps is estimating and ordering the required number of seeds. This calculation is typically based on a nomogram that relates prostate volume to total activity. At our institution, an additional 25 seeds are added—10 for calibration verification and 15 as a safety margin. However, the number of seeds actually used is consistently lower than those ordered, leading to a considerable surplus. The objective of this work is to reduce the number of ordered seeds by approximately 10%, thereby minimizing both costs and radioactive waste. Material/Methods: A total of 197 patients treated with I-125 seeds were analyzed, with prostate volumes ranging from 40.13 to 88.86 cc. Differences between pre-planning volumetry and intraoperative ultrasound measurements were assessed. The number of unused seeds per patient was also evaluated in relation to prostate volume, and an alternative nomogram based on actual activities was explored. Results: Patients were divided into two groups based on prostate volume, with an empirically defined threshold of 45 cc. For volumes greater than 45 cc (n = 71), no seed shortages occurred. For volumes below 45 cc, shortages appeared in 29 cases (15%), with only 11 cases (5.6%) showing a deficit greater than five seeds.
patients who experienced biochemical relapse. Material/Methods: Patients with localized low-risk (LR) or favourable- intermediate-risk (FIR) prostate cancer ( ≤ T2b, PSA ≤ 15 ng/mL, ISUP ≤ 2) were enrolled in the SiFEPI phase II prospective trial (NCT02104362) which investigated the efficacy and toxicity of a single fraction (20 Gy) of high-dose-rate brachytherapy (HDR-BT). The present updated analysis includes all available clinical and biological data, up to September 2025. Biochemical recurrence (BR) was defined according to ASTRO criteria. In the event of rising PSA, patients underwent MRI and PET imaging, and prostate biopsies were systematically proposed to confirm local relapse.Relapse type (local, nodal or metastatic) and site were recorded.All BR cases were reviewed in a multidisciplinary tumour board to select salvage treatment, including surgery, EBRT, androgen deprivation therapy, or active surveillance. For patients managed with salvage EBRT, oncological outcomes and late toxicity were specifically analysed. Results: From March 2014 to October 2017, 33 patients were enrolled in the SiFEPI trial. After a median follow-up (MFU) of 115 months [95-139], the 10-year biochemical relapse-free survival (bRFS), local relapse-free survival (lRFS), and metastatic relapse-free survival (mRFS) were 45% [29–68], 45% [30–69], and 94% [85–100], respectively.Ten-year disease-free survival (DFS), cancer-specific survival (CSS), and overall survival (OS) were 31% [18–53], 100%, and 79% [64–96]. Eighteen patients (54%) developed BR with a median time interval between HDR-BT and BR of 60 months[20– 136].Among these, 10 pts (62.5%) received salvage EBRT.In this subgroup, with a MFU of 66 months[12– 101], 5-year bRFS, lRFS, and mRFS were67% [30–100], 100% and 67% [30–100], while DFS, CSS, and OS were67% [30–100], 100%, and 100%. After EBRT, late genitourinary (GU), gastrointestinal (GI), and sexual toxicities were observed in 8 pts (80%), 4 pts (40%), and 6 pts (60%), respectively. Among them, 2 pts (20%) experienced G3 toxicity (1 pt: GU and GI events; 1 pt: GU toxicity only). Conclusion: Although single-fraction HDR-BT is no longer recommended due to suboptimal biochemical control, these long-term data show that salvage EBRT after HDR-BT achieves acceptable oncological control with manageable toxicity.Re-irradiation could be considered as a valuable option for carefully selected patients relapsing after HDR-BT delivered in two- fraction regimens. Keywords: prostate cancer, brachytherapy, single fraction
PROPOSED METHODOLOGYSince larger prostates tend to produce seed surpluses, treatment days are organized to pair one patient from each group. This pairing allows the surplus from large-volume implants to compensate for possible shortages in smaller ones. Additionally, the 15 safety-margin seeds are omitted for patients with prostate volumes over 45
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