ESTRO 2025 - Abstract Book

S371

Brachytherapy - Urology

ESTRO 2025

Both HDR-BT+EBRT and LDR-BT+EBRT yielded excellent 20-year outcomes. These results corroborate earlier 10-year findings, particularly the unfavorable GUTFS for the LDR group. Gleason score and PSA at diagnosis emerged as significant long-term risk factors.

Keywords: LDR, HDR, prostate

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Mini-Oral Long-term outcomes of LDR brachytherapy plus EBRT in prostate cancer: Influence of androgen deprivation therapy on disease progression and toxicity Alai Goñi Ramirez 1 , Macarena Sevilla 2 , Mikel Larruskain 2 , Maider Alberich 2 , Darya Chyzhyk 2 , Mikel Egiguren 1 , Vicent Pastor 3 , Albert Bartres 3 , Eva Maria Saenz de Urturi 1 , Daniel Alberto Roura 1 , María Pagola 1 , Amaia Sanchez 1 , Usoa Iceta 1 , Nuria Bultó 1 , Sara Palacios 1 , Ane Mugica 1 , Leyre Gonzalez 1 , Intza Uranga 1 , Maider Campo 1 , Ane Dehesa 1 , Ane Otaegui 1 , Xabier Gurutzeaga 1 , Beraldo Martinez 1 , Julian Minguez 1 , Arrate Querejeta 1 1 Radiation Oncology, Onkologikoa - UGC Oncología Gipuzkoa, San Sebastian, Spain. 2 Data Science, NARU Intelligence, San Sebastian, Spain. 3 Medical Physics, Onkologikoa - UGC Oncología Gipuzkoa, San Sebastian, Spain Purpose/Objective: This study aims to assess the impact of Androgen Deprivation Therapy (ADT) on long-term biochemical failure, metastasis, cancer-specific survival, and toxicity outcomes in prostate cancer patients treated with low-dose-rate brachytherapy (LDR-BT) plus external beam radiotherapy (EBRT). Material/Methods: Between 2001 and 2015, 556 patients received LDR-BT combined with EBRT, with 268 (48.2%) receiving at least three months of ADT and 288 (52.8%) treated without ADT. The mean follow-up was 146 months (range: 28–271 months). Biochemical recurrence-free survival (BFS), metastasis-free survival (MFS), cancer-specific survival (CSFS), genitourinary toxicity-free survival (GUTFS), and gastrointestinal toxicity-free survival (GITFS) were estimated using the Kaplan-Meier method. Patients in the ADT and non-ADT cohorts were matched 1:1 using propensity scores (PS), accounting for confounding factors such as PSA at diagnosis, age at treatment, prostate volume, timing of EBRT relative to LDR-BT, Gleason score, and tumor stage. Kaplan-Meier survival curves were compared between matched cohorts using the log-rank test. Results: In the overall population, the median age was 70.82 years (Q1 65.7; Q3 74.4) and the median PSA at diagnosis was 9.81 ng/mL (Q1 7; Q3 13.92). The most common tumor stages were T1c (38.31%), T2c (27.7%), and T2b (21.04%), and most patients had Gleason scores of 7 (45.68%) or 6 (37.41%). CSFS rates were 99.08% at 10 years, 97.02% at 15 years, and 93.92% at 20 years. BFS and MFS rates were 90.45% and 96.43% at 10 years, 82.09% and 92.27% at 15 years, and 79.43% and 90.24% at 20 years, respectively. After matching, 200 patients were included (100 ADT, 100 non-ADT), though balanced matching was not achieved for patients with PSA >35 or Gleason scores >9. Stratification by ADT status revealed no significant differences in overall survival (OS), BFS, MFS, or GITFS. However, ADT was associated with a significantly lower GUTFS: 82.9% (95% CI 73.5–89.2) vs. 70.39% (95% CI 59.9–78.6) at 10 years (p = 0.029), and 74.14% (95% CI 60.7–83.6) vs. 41.89% (95% CI 17.8–64.5) at 16 years (p = 0.015).