S151
Brachytherapy - Urology
ESTRO 2026
Digital Poster 97 Influence of Brachytherapy Dose and Other Factors on Outcomes in HDR Prostate Brachytherapy Monotherapy Pooriwat Muangwong 1,2 , Peter Ostler 1 , Robert Hughes 1 , Roberto Alonzi 1 , Mohammed Abdul-Latif 1 , Peter Hoskin 1,3 1 Clinical Oncology Department, Mount Vernon Cancer Centre, Northwood, United Kingdom. 2 Division of Radiation Oncology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand. 3 Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom Purpose/Objective: To investigate the association between brachytherapy dose and oncological outcomes in patients with localized prostate cancer treated with high–dose–rate (HDR) brachytherapy monotherapy, and to identify clinical and brachytherapy factors influencing
dosimetric quality. Material/Methods:
We retrospectively analyzed 286 consecutive patients with localized prostate cancer who underwent HDR brachytherapy monotherapy (19–20 Gy × 1, 13 Gy × 2, or 10.5 Gy × 3) between 2005-2013. Clinical data included age, PSA, Gleason score, T stage, and androgen deprivation therapy (ADT) use. Dosimetric parameters were extracted from treatment plans and included EQD ₂ D90, V100, V150, and the dose homogeneity index (DHI). Biochemical relapse-free interval (bRFI) and overall survival (OS) were estimated using Kaplan–Meier methods and compared by EQD ₂ D90 groups. Cox regression was used to assess associations between EQD ₂ D90 (per 10 Gy increase) and outcomes, overall and within fractionation subgroups. Linear regression identified predictors of dosimetric parameters and applicator use. Results: At median follow-up of 108 months for bRFI and 120 months for OS, the 10-year bRFI and OS rates were 72.8% and 78.3%, respectively. In the overall cohort, EQD ₂ D90 was not significantly associated with bRFI or OS. Subgroup analysis showed a survival benefit in the 2-fraction regimen, where each 10 Gy increase in EQD ₂ D90 was associated with a 28% reduction in mortality risk (HR 0.72; p = 0.03). Other dosimetric parameters (V100, V150, DHI) showed no significant associations with outcomes. Higher EQD ₂ D90 was associated with more applicators and single-fraction treatment. Larger prostate volume predicted lower V150 and higher DHI, while the 2-fraction regimen was associated with higher V150 but lower DHI. V100 increased with applicator number, whereas Gleason score ≥ 8 was associated with reduced V100.
Conclusion: In HDR brachytherapy monotherapy for prostate cancer, higher EQD ₂ D90 did not improve bRFI or OS overall, though improved survival was observed in the 2-fraction regimen. Applicator number and prostate volume strongly influenced dosimetric quality. Further prospective and multi-institutional studies are warranted to validate these findings and guide dose optimization strategies in HDR brachytherapy. Keywords: HDR brachytherapy, Dosimetry, Prostate cancer Digital Poster Highlight 358 Ten-year outcomes of single-fraction HDR brachytherapy for prostate cancer: Results from the SiFEPI phase II prospective trial. Marie-Colombe Schmittbiel 1 , Tanguy Pace-Loscos 2 , Mathieu Gauthier 1 , Delphine Marotte 1 , Edouard Herin 3 , Renaud Schiappa 2 , Jean-Michel Hannoun-Levi 1 1 Radiation Oncology, Antoine Lacassagne Cancer Center, University Côte d’Azur, Nice, France. 2 Statistics, Antoine Lacassagne Cancer Center, University Côte d’Azur, Nice, France. 3 Radiology, Antoine Lacassagne Cancer Center, University Côte d’Azur, Nice, France Purpose/Objective: To report the long-term results of the Single Fraction Early Prostate Irradiation (SiFEPI) phase II trial and to evaluate oncological outcomes and late toxicity after salvage external beam radiation therapy (EBRT) in
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