ESTRO 2025 - Abstract Book

S2049

Clinical - Urology

ESTRO 2025

We present our survival and toxicity findings following pelvic re-irradiation in the oligometastatic prostate cancer setting.

Material/Methods: Patients treated with SBRT irradiation to pelvic lymph nodes, seminal vesicles or the bony pelvis following radical radiotherapy to the prostate or prostate bed were identified between July 2011 and September 2021. Retrospective data was collected from our hospital electronic records. We recorded patient demographics, the primary and salvage SBRT treatment dose and fractionation, CT CAE toxicity data and the time interval from SBRT treatment to subsequent lines of treatment. Patients were censored at their most recent follow-up date in September 2023. Statistical analysis was performed using written code from Python 3.10 in PyCharm CE and Lifeline package to produce Kaplan-Meier curves. Results: 74 patients in total were identified. The median age (at time of re-irradiation) was 69 years old, with a median follow up period of 4.3 years. 11 patients received simultaneous SBRT treatments to more than one site within the pelvis, whilst 12 patients received SBRT to a second site sequentially. The median duration from primary radiotherapy treatment to pelvic SBRT for oligometastatic disease was 61.4 months. Our patient treatment data is summarised in Table 1.

Median PFS following re-irradiation was 20.67 months (95% CI 16.93-30.63 months). 24% of patients did not require any further treatment following their primary SBRT treatment. Only 12% of patients recurred locally at the previously treated lesion. For those requiring sequential SBRT for oligometastatic disease, the median time between SBRT treatments was 21.9 months. Overall SBRT treatment was well tolerated with 17% of patients developing grade 1 gastrointestinal toxicity and 3% grade 2. 21% of patients developed grade 1 genitourinary toxicity, 7% grade 2 and 1% developed grade 3 radiation cystitis.