ESTRO 2025 - Abstract Book

S396

Brachytherapy - Urology

ESTRO 2025

Keywords: electromagnetic tracking, implant reconstruction

References: [1] Androulakis, Ioannis, et al. "417: Electromagnetic tracking reveals reconstruction errors in intraoperative TRUS– based prostate HDR-BT." Radiotherapy and Oncology 194 (2024): S395-S398. [2] Androulakis, Ioannis, et al. "Assessment of integrated electromagnetic tracking for dwell position monitoring in a clinical HDR brachytherapy setting for prostate cancer." Radiotherapy and Oncology 200 (2024): 110501. [3] Lavallee, Marie-Claude, et al. "US-guided EM tracked system for HDR brachytherapy: A first in-men randomized study for whole prostate treatment." Brachytherapy 23.1 (2024): 64-72.

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Mini-Oral Long-term outcomes of HDR monotherapy with a single fraction of 19 Gy for localized prostate cancer: A multicentered retrospective analysis Wiwatchai Sittiwong 1 , Anna Lydon 2 , James Wylie 3 , John Logue 3 , Cathy Taylor 3 , Peter Ostler 1 , Robert Hughes 1 , Roberto Alonzi 1 , Peter Hoskin 1 1 Radiotherapy, Mount Vernon Cancer Centre, London, United Kingdom. 2 Radiotherapy, Royal Devon and Exeter Hospital, Exeter, United Kingdom. 3 Radiotherapy, The Christie NHS Foundation Trust, Manchester, United Kingdom Purpose/Objective: To assess the clinical outcomes, toxicity, and prognostic factors in patients with localized prostate cancer receiving single dose high-dose-rate (HDR) brachytherapy as monotherapy with long-term follow-up. Material/Methods: This retrospective analysis was conducted across three centres in the UK. All patients received HDR brachytherapy delivered in a single fraction of 19 Gy following an agreed common protocol. Kaplan-Meier estimates were calculated at 5 and 8 years for biochemical progression-free survival (bPFS), local recurrence-free survival (LRFS), nodal recurrence-free survival (NRFS), distant metastasis-free survival (DMFS), and overall survival (OS). Univariate and multivariate Cox regression analysis was performed to identify prognostic factors. Genitourinary (GU) and gastrointestinal (GI) toxicities were graded according to CTCAE. Quality of life (QoL) was assessed using International Prostate Symptom Score (IPSS), International Index of Erectile Function (IIEF), and Functional Assessment of Cancer Therapy–Prostate (FACT-P) questionnaire. Results: Among the 259 patients included in this analysis, the median age was 79 years (IQR 75.4–83.8). The baseline patient characteristics are shown in Table1. With a median follow-up of 95 months, the rates of 5/8-year bPFS, LRFS, NRFS, DMFS and OS were 76.4%/64.6%, 97.4%/92.0%, 98.4%/97.2%, 95.8%/93.7% and 93.0%/82.5%, respectively. Patients classified as low-risk exhibited significantly higher bPFS compared to those with intermediate- to high-risk disease (HR 7.39, 95% CI 1.03–35.13, p = 0.018), as shown in figure 1. However, no significant differences were observed in other outcomes. Univariate and multivariate analyses identified the presence of subcentimetered pelvic lymph nodes on pre-brachytherapy MRI as significantly associated with worse bPFS (HR4.94,95%CI 3.20–7.84, p < 0.001), LRFS (HR11.96,95%CI 3.29–44.44, p <0.001), DMFS (HR13.23,95%CI 2.87–60.94, p =0.001), and OS (HR13.23,95%CI 2.87–60.94, p =0.001). T-stage was also predictive of LRFS (HR4.28,95%CI 1.31–13.97, p =0.016). The actuarial rates of ≥grade 2 acute and late GU toxicities were 3.1% and 19.3%, respectively, while GI toxicities were 0.8% and 1.5%, respectively. The most common late GU symptoms were urgency and urethral stricture, and the most frequent late GI symptom was diarrhoea. QoL assessments showed significant changes between baseline and post-treatment worst scores: mean IPSS increased by +7.14±8.24 points ( p < 0.001), mean IIEF decreased by −2.95±6.79 points ( p = 0.043), and mean FACT-P increased by +15.17±25.78 points ( p = 0.02).