ESTRO 2025 - Abstract Book

S373

Brachytherapy - Urology

ESTRO 2025

Results: Fourty-one patients (NCCN 48.8% UIR, 43.9% HR and 7.3% VHR) completed treatment and reached at least 12 months of follow-up (FU) at the time of the current analysis. Median FU was 16 months (IQ range 9-24). Median age was 71.7 years, median PSA before treatment was 8.4 ng/mL (5.0-28.3) and median volume of the prostate was 36.6 cc (14.9 68.2). Short-term ADT was administered to 43.9% of patients whereas 48.8% received long-term ADT, the rest of the patients did not receive hormonal therapy. No severe (Grade ≥3) acute events were recorded. An increase was observed in the cumulative incidence of grade 2 GU toxicity, owed mainly to nocturia (2.4% at 3 months, 4.9% at 6 months and 26.8% at 12 months), with grade 1 remaining stable over this period. Regarding GI toxicity, grade 1 and 2 incidences remained almost identical over this time interval. A significant decline from baseline compared to 3 months post treatment was observed both in hormonal and sexual domains, with high severity exhibited as a worsening from 12% to 38% and from 0% to 5%, respectively. No other domains exhibited any significant decline (urinary incontinence, irritation/bother, and bowel). Conclusion: The evaluation of the primary results of the presented prospective phase II trial suggests that this HF combined radiotherapeutic scheme is well-tolerated, presenting no early severe adverse events. Moreover, patient reported outcomes confirm these results, since no significant decline in any domain from baseline values was recorded. Digital Poster Planning feasibility study for HDR-brachytherapy to treat muscle invasive bladder cancer Liam Mannion 1,2 , Emma-Louise Jones 2 , Jeyaanth Venkatasai 2 , Simon Hughes 2 , Vinod Mullassery 2 1 City St George’s, University of London, Radiography, London, United Kingdom. 2 Guy’s and St Thomas’ NHS Foundation Trust,London, UK, Guy's Cancer, London, United Kingdom Purpose/Objective: To evaluate the feasibility of producing high dose rate brachytherapy (HDR-BT) plans for muscle invasive bladder cancer (MIBC). Material/Methods: CT data sets from five patients previously treated with external beam radiotherapy for MIBC were used to create 15 separate HDR-BT plans. The feasibility of delivering these plans was modelled on several considerations: anatomical location within the bladder, tumour size, optimal catheter positioning, total dose, fractionation and dose to surrounding organs at risk (OARs), the small bowel and rectum. New clinical target volumes (CTVs) were created for each plan. Using these data sets we simulated catheter placements within the outlined CTVs to assess the D90, in addition to the D2cc of OARs. Total doses to the CTVs and OARs were reported using equivalent doses in 2 Gy per fraction (EQD2). Results: We were able to produce plans for 13/15 CTV volumes with a median (per fraction) EQD2 CTV D90 of 2.42 Gy {2.25 2.69 SD 0.11}. 46% (n =6) of our CTVs resulted in good dose distribution, with two receiving ≥85% (CTV 3 and 13) and four (CTV 7, 8, 11, and 15) receiving 75-80% of the prescribed dose. The median EQD2 D2cc (25 Gy in 10 fractions) delivered to the bladder, small bowel, and rectum 35.2 Gy {27.8-44.2 SD 4.2}, 17.98 Gy {16.2-22.7 SD 1.61} and 15.68 Gy {15.3-15.9 SD 0.2} respectively. Keywords: PSMA-PET, prospective trial, Combined Radiotherapy 537