S1149
Clinical - Urology
ESTRO 2026
Digital Poster Highlight 655
study across four tertiary hospitals in London. Systemic and radiotherapy treatment databases between 2015 and 2025 were reviewed to identify eligible patients. Inclusion criteria comprised patients with low-volume po- mHSPC treated with pelvic all-site radical radiotherapy. Biochemical progression was defined by Phoenix criteria. Progression-free survival (PFS) and OS were estimated using the Kaplan–Meier method. Results: A total of 4456 patients were screened and 45 finally included. Median age (interquartile range) was 65 (61–71), and median prostate-specific antigen (PSA) at diagnosis was 25 ng/mL (11–54). 98% had performance status 0–1, and 84% presented with de novo metastatic disease. Conventional imaging was used in eight (18%) and novel imaging (choline or prostate-specific membrane antigen PET) in 37 (82%) patients; 12 underwent both, with 10 showing concordant evidence of metastases. Neoadjuvant docetaxel was administered to 22 (49%) patients, 20 (44%) received an androgen receptor pathway inhibitor (ARPI), one (2%) received both docetaxel and enzalutamide, and two (4%) received ADT alone. Conventional fractionation was most common (66%) with 74–78Gy/37–39 fractions to the prostate and 55–60.8Gy delivered to the metastases. After a median follow-up of 46 months, 33 (73%) patients achieved an undetectable PSA level. Four (9%) biochemical and six (13%) radiological progression events were recorded, along with three (7%) deaths. The estimated 3-year biochemical PFS, radiological PFS, and OS rates were 95%, 92%, and 97%, respectively. In total, 21 (47%) patients successfully discontinued ADT following a median of 35 months of therapy (13 following docetaxel, six following ARPI, one following both docetaxel and enzalutamide, and one treated with ADT monotherapy). 10 (48%) had testosterone recovery. Two (20%) patients experienced disease progression, with times to progression of 38- and 59-months following testosterone recovery. Conclusion: These data highlight excellent oncological outcomes following pelvic all-site radiotherapy. Furthermore, a proportion of patients with po-mHSPC were able to come off all systemic therapy with ongoing disease response, suggesting a proportion of patients with metastatic disease at diagnosis may not require life-long treatment. These findings require validation in larger and prospective studies. Keywords: Oligometastatic cancer, radical radiotherapy
The association between acute, subacute, and late genitourinary quality of life with prostate SBRT Li X Chan 1 , Jarad M Martin 2 , Mark Sidhom 1 , David Pryor 3 , Joseph Bucci 4 , Lucy Leigh 5 , Eric Wegener 2 1 Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia. 2 Radiation Oncology, University of Newcastle, Newcastle, Australia. 3 Radiation Oncology, Princess Alexandra Hospital, Brisbane, Australia. 4 Radiation Oncology, St George Hospital, Sydney, Australia. 5 Data Sciences, Hunter Medical Research Institute, Newcastle, Australia Purpose/Objective: Emerging evidence has shown an association between acute and late genitourinary toxicity following prostate radiotherapy1. However, this is not established within the SBRT setting. Furthermore, prostate SBRT is associated with a subacute flare in GU toxicity, but whether this translates into longer-term morbidity is unknown. PROMETHEUS (ACTRN12615000223538) was a multicentre phase 2 trial that investigated the use of SBRT as a virtual high-dose rate brachytherapy boost for prostate cancer2. We conducted a post-hoc analysis to examine any correlation between acute, subacute, and late genitourinary quality of life (QOL). Material/Methods: 151 men were included with a median follow-up of 60 months. The relationship between acute (end of treatment [EOT]), subacute (12 M), and late (36M and 60 M) QOL changes were examined based on EPIC-26 scores and the occurrence of a minimal clinically important difference (MCID)3. Analyses were performed separately for urinary incontinence, obstructive, and irritative domains. Univariable and multivariable logistic regression analyses were performed to assess the association between variables. Results: The changes in MCID of the cohort at different time points are demonstrated in Figures 1 and 2. On multivariable analysis, development of late urinary incontinence MCID was associated with MCID at both EOT (OR 3.55 [1.42-8.92], p = 0.01) and 12M (OR 8.72 [3.53-21.56], p <0.01). Other factors associated with late urinary incontinence MCID were TURP (OR 6.11[1.56–23.89], p = 0.01), and the use of Rectafix compared to SpaceOAR rectal spacing (OR 2.6 [1.09- 6.23], p = 0.03). Late urinary irritative MCID was associated with men who had poor baseline irritative function and those who experienced subacute irritative toxicity at 12M (OR 7.95 [1.71-36.91], p < 0.01 and 5.47 [2.11–14.18], p < 0.01, respectively). There were no associations found with late obstructive urinary
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