ESTRO 2025 - Abstract Book

S2116

Clinical - Urology

ESTRO 2025

Purpose/Objective: The low α/β ratio for prostate cancer (PCa) suggests a benefit of ultra-hypofractionation (UHF). When treating the entire seminal vesicles (SV), UHF is challenging as the SV require a large PTV-margin (8mm). The UPRATE trial (clinicaltrials.gov; NCT05361902) aims to prove feasibility of SV PTV-margin reduction in low volume metastatic PCa, combining online adaptation, using an in-room CT-scanner on rails with intra-fraction fiducial tracking. Here, we report the final results. Material/Methods: In this single-arm, single-centre, phase 2 trial 34 men with histologically and radiologically proven metastatic PCa, referred for local radiotherapy according to the STAMPEDE trial were included [1]. Patients were treated with six weekly online adapted fractions of 6 Gy. CTV contained the prostate and base or entire SV (at treating physician’s discretion) and PTV- margins of 3mm (prostate) and 5mm (SV). Plans were made aiming for PTV V95 ≥99% and adherence to OAR constraints. Simulated plans incorporating the entire SV were generated to prove the feasibility of PTV-margin reduction. Relevant dosimetric parameters were obtained and recorded for all patients by transferring both the adapted (delivered or simulated) and non-adapted plans, based on a fiducial match, onto the post-fraction CT-scan. The primary endpoint of PTV-margin reduction (5mm) was deemed feasible when 33/34 patients were treated successfully. ‘Successful’ being defined as minimum 5/6 fractions with SV V95 ≥99%. Genitourinary (GU) and gastrointestinal (GI) toxicities (CTCAE v5.0) were recorded and a questionnaire (Acute RTOG EORTC) was filled in by all patients at baseline, during treatment and at 3 month follow-up. Results: The primary endpoint was met as 33/34 (delivered or simulated) treatments were successful. Table 1 shows population average target coverages for adapted and non-adapted plans. One of the 23 simulated treatments was considered unsuccessful, due to large intra-fraction bladder volume changes (<200mL pre-fraction to >800mL post fraction) during two fractions. In contrast, only 24/34 non- adapted treatments were ‘successful’.