S172
Brachytherapy - Urology
ESTRO 2026
and cases of isolated SV relapse were identified. Recurrence after initial treatment was defined as prostate-specific antigen (PSA) ≥ 2.0 ug/L above nadir
or radiological evidence of disease. Patients underwent transrectal ultrasound-guided
transperineal interstitial catheter implantation under regional or general anaesthesia. Patients received either a single 19 Gy fraction or 26 Gy in 2 fractions over 2 consecutive days using an Iridium-192 (I192) radioactive source. Follow-up included PSA assessment and follow-up time was calculated from date of salvage BT. Progression was defined as PSA failure (PSA level of ≥ 2.0 ug/L above nadir as per the Phoenix definition) or radiological evidence of disease recurrence. Outcomes included progression free survival (PFS), overall survival (OS) and time to next line of treatment (TTNT). Results were analysed using ‘R’ (version 4.4.2) for Kaplan-Meier survival analysis. Results: Twenty-three cases of isolated SV relapse of prostate cancer were identified and patient characteristics are summarised in Table 1. Median patient age at salvage BT was 73 and median PSA prior to salvage BT was 3.8 ug/L. Majority (61%) patients had received low-dose rate seed brachytherapy at initial diagnosis. Six patients (26.1%) received androgen deprivation therapy (ADT) prior to salvage BT. Seventeen patients received salvage BT with one 19 Gy fraction and 6 patients received 26 Gy in 2 fractions. One patient received salvage BT to a right SV relapse in July 2018 but developed an out-of-field right SV recurrence in Dec 2018 and received further salvage BT. Median follow-up was 23 months. At time of analysis, 11 (47.8%) patients had relapsed, and 12 (52.2%) patients remained progression-free. The median time to next line of treatment was 56 months (Figure 1). Median PFS was 39 months, and median OS was not reached.
TTCP was short among tumor types with a median of 0.92 years (95% CI 0.7-1.4), whereas median OS was 7 years (95% CI 6.3-10.3). Patients with renal cell and prostate carcinoma showed comparatively improved median OS results with 8.9 and 6.5 years, respectively. Recurrence occurred in 82% of patients after IORT during follow-up, 60% of which were in field. Conclusion: Despite extensive prior treatments in the analyzed cohort, IORT remains a feasible and safe option for advanced tumors and may delay progression and improve OS. Due to limited data, IORT should be performed in specialized centers. Tumor entities differ in their response to IORT, primarily due to variations in radiosensitivity, which represents an important limitation. Further research is needed to identify the patient groups most likely to benefit from this treatment. Keywords: IORT, urological cancer Focal salvage high dose rate brachytherapy for isolated seminal vesicle relapse of prostate cancer Tracy Lim Yew Fai 1 , Amani A Chowdhury 1 , Roberto Alonzi 1 , Peter Ostler 1 , Robert Hughes 1 , Milan Anjanappa 1 , Mohammed Abdul-Latif 1 , Hannah Tharmalingam 1 , Gillian Marks 1 , Ami Mehta 1 , Peter J Hoskin 1,2 1 Department of Radiotherapy, Mount Vernon Cancer Centre, Northwood, United Kingdom. 2 Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom Digital Poster Highlight 4010 Purpose/Objective: Functional imaging has facilitated earlier detection of small biochemical recurrences of prostate cancer with better opportunity for earlier salvage therapy. Although relapses are often predominantly extra- prostatic, around a third of recurrences are local. Isolated seminal vesicle (SV) recurrences are uncommon but have been observed and there is no consensus on the best management approach. Material/Methods: A single institution retrospective analysis of 173 patients receiving salvage prostate brachytherapy between March 2013 and August 2025 was performed
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