S178
Brachytherapy - Urology
ESTRO 2026
Purpose/Objective: Prostate cancer (PCa) is one of the most prevalent neoplasms in men and, despite therapeutic advances, between 20% and 40% of patients treated with external radiotherapy (RT) experience local recurrence. In these cases, re-irradiation with low- or high-dose-rate (LDR or HDR) brachytherapy represents a potentially curative alternative, especially in patients with a low risk of systemic spread and a good life expectancy. The main objective of the study is to describe biochemical recurrence-free survival (BRFS). Secondary objectives include evaluating local control (LC), metastasis-free survival (MFS), overall survival (OS), adverse effects, and associated clinical factors in order to provide local evidence to optimise patient selection and improve clinical decisions regarding re- irradiation. Material/Methods: Observational, longitudinal, retrospective study of a cohort of patients diagnosed with local recurrence of CaP treated with low-dose rate (LDR) or high-dose rate (HDR) brachytherapy, who had previously received radical external radiotherapy and regardless of Gleason score at relapse. All patients were staged with PET-PSMA, prostate MRI, and biopsy to confirm recurrence. In LDR brachytherapy the dose administered was 145 Gy and in the case of HDR, the most frequent fractionation was 3 fractions of 10 Gy.Concomitant or adjuvant hormonal treatment was administered in 48.7% of patients. The RTOG scale was used to measure toxicity. Results: Between 2017 and 2024 a total of 39 patients with locally recurrent PCa after external radiotherapy were treated with salvage brachytherapy (28 with LDR and 11 with HDR). With a median follow-up of 54.3 months, the BRFS was 89.7%. Local progression occurred in 3 patients (7.7 %) and one patient (5.1 %) developed metastases during follow-up. OS was 100%. Acute genitourinary toxicity G3 was 17.9%, with late toxicity at 15.4%. There was no gastrointestinal toxicity > G3. No statistically significant associations were found between BRFS and clinical, pathological or dosimetric variables, either in bivariate or multivariate analyses.
vs ≥ 100 %, Dose Non-Uniformity Ratio, Dose Homogeneity Index, and Conformity Index), were analyzed. Primary endpoint: biochemical progression- free survival (bPFS); secondary endpoint: metastasis- free survival (MFS). Overall survival (OS) were reported at 5- and 10-year follow-up without specific analysis. Results: After a median follow-up of 69 months, the 5- and 10- year rates were 97.4% and 88.6% for OS; 95.4% and 91.8% for local control (LC); 93.3% and 86.2% for MFS; and 87.3% and 60.7% for bPFS.For bPFS, no clinical or dosimetric variable reached statistical significance in univariate Cox analysis. A non-significant trend was observed for EQD2 ≥ 110 Gy (HR 0.64; p=0.119). In multivariable analysis, only Gleason 8–10 was retained (HR 0.28; 95% CI 0.06–1.18; p=0.082).For MFS, the NCCN risk group was significantly associated with outcome ( χ² =9.66; p=0.008), with inferior results in the very-high-risk subgroup (HR 4.01; 95% CI 1.52–10.58; p=0.005). In the multivariable model, no variable remained independently significant; the final model retained DHI_s (HR 0.48; 95% CI 0.21–1.10; p=0.082) and CI_s (HR 0.96; 95% CI 0.91–1.02; p=0.164), with proportional hazards satisfied.Acute ≥ grade 2 toxicities occurred in 4.5% (genitourinary) and 1.5% (gastrointestinal) of patients. Late ≥ grade 2 toxicities occurred in 3.6% (GU) and 1.8% (GI), totaling 5.4% of patients. Conclusion: A single-fraction HDR brachytherapy boost combined with external beam radiotherapy achieves excellent long-term biochemical and metastasis-free control, with 10-year bPFS and MFS rates of 60.7% and 86.2%, respectively, and minimal late toxicity (<6% grade ≥ 2). No clinical or dosimetric variable independently predicted biochemical outcomes, although EQD2 ≥ 110 Gy and higher Gleason score showed non- significant protective trends, likely reflecting treatment intensification. For MFS, only the very-high-risk NCCN group was associated with inferior outcomes. These results support the durability and safety of single- fraction HDR boost regimens within contemporary radiotherapy protocols. Keywords: prostate; HDR brachytherapy; biochemical control Digital Poster 5038 Rescue brachytherapy in local recurrence of prostate cancer Raquel Galindo Fuentes 1 , Paula Rodrigo Molinos 1 , Cristina Ortega Monedero 2 , Sonia García Cabezas 1 , Amalia Palacios Eito 1 1 Oncología Radioterápica, Hospital Reina Sofía, Córdoba, Spain. 2 Student, UCO, Córdoba, Spain
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