ESTRO 2025 - Abstract Book

S374

Brachytherapy - Urology

ESTRO 2025

Conclusion: HDR-BT is feasible for solitary tumours (less than or equal to max diameter 5cm) located in the anterior dome of the bladder. Achieving suitable catheter placement and subsequent treatment is difficult for tumours in the lateral walls and should be considered on an individual case basis.

Keywords: Muscle invasive bladder cancer

605

Digital Poster Are low PSA nadir and delayed time to PSA nadir the goals to reach in patients with prostate cancer treated with LDR-BT? Aldara Candal Melendrez 1 , Ana María Vílchez Simó 1 , Beatriz Vázquez Barreiro 1 , Patricia Willisch Santamaría 1 , Benito Andrade Álvarez 2 , Enrique Cespón Outeda 3 , Íñigo Nieto Regueira 1 , María Luisa Vázquez de la Torre González 1 , Víctor Manuel Muñoz Garzón 1 1 Radiotherapy Oncology, Hospital Meixoeiro, Vigo, Spain. 2 Radiophysics, Hospital Meixoeiro, Vigo, Spain. 3 Urology, Hospital Álvaro Cunqueiro, Vigo, Spain Purpose/Objective: To evaluate PSA response after low-dose-rate brachytherapy (LDR-BT) in patients with very-low (VLR), low (LR), and intermediate risk (IR) prostate cancer. Material/Methods: This retrospective study included patients who underwent treatment with I-125 LDR-BT, delivering a total dose of 145Gy at Hospital Meixoeiro in Vigo (Spain) between 2012-2022. Primary endpoints were value of PSA nadir, time to PSA nadir, rate of biochemical failure (BF) defined by Phoenix criteria, and biochemical progression-free survival (bPFS). Results: A total of 250 patients were included with a median follow-up of 87 (10-155) months. Mean age at diagnosis was 69 (47-82) years. The cohort was stratified into three risk groups based on 2018 NCCN guidelines: 114 patients in the VLR, 101 in the LR, and 35 in the IR group, 2 of which were classified as unfavorable-IR. Mean CTV-D90 was 111.41% (90.88%-121.44%), and CTV-V100 was 94.52% (84.23%-99.8%). Median time to PSA nadir was 52.2 months for the VLR group, 39.7 for LR, and 33.17 for IR (p<0.001). Median value of PSA nadir was 0,08, 0,14, and 0,17 ng/ml, respectively for each group (p<0.001). BF occurred in 7,8% in VLR, 19,8% in LR and 17% in IR group. bPFS was 81 months for VLR group, 68.14 for LR and 66.94 for IR (p=0.011). Lower PSA nadir values have a significaltly lower risk of BF (HR=2.58, p=0.012). A delayed time to PSA nadir is associated with a decreased risk of BF (HR=0.91, p<0.001). No urinary or rectal toxiciy greater than grade 2 was observed.