ESTRO 2025 - Abstract Book

S1920

Clinical - Urology

ESTRO 2025

1026

Digital Poster SABR for high and very-high risk prostate cancer: early insights into feasibility and safety Helena Barbara Zobec Logar 1,2,3 , Angel Montero 1 , Ovidio Hernando 1 , Mercedes Lopez 1 , Jeannette Valero 1 , Raquel Ciervide 1 , Beatriz Alvarez 1 , Emilio Sanchez 1 , Leyre Alonso 4 , Mariola Garcia-Aranda 1 , Xin Chen-Zhao 1 , Carmen Saiz 1 , Bruno Zambrana 1 , Alejandro Prado 4 , Rosa Alonso 1 , Pedro Fernandez-Leton 4 , Carmen Rubio 1 1 Department of Radiation Oncology, HM Hospitales, Madrid, Spain. 2 Department of Radiation Oncology, Institute of Oncology, Ljubljana, Slovenia. 3 Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia. 4 Department of Medical Physics, HM Hospitales, Madrid, Spain Purpose/Objective: To evaluate feasibility and tolerance profile of an UHF urethra-sparing SABR protocol in high and very high-risk prostate cancer (HR-Pca). Material/Methods: From March 2020 to August 2022, 70 patients with HR-Pca were enrolled. Complete characteristics are detailed in Table 1. The dose for the prostate, seminal vesicles and simultaneous boost to the positive lymph nodes was 40 Gy in 5 fractions (BED=253.3 Gy, a/b 1.5 Gy) and for the elective lymph nodes (ENI) 26 Gy in 5 fractions (BED=116.1 Gy, a/b1.5 Gy) on every other day with VMAT technique. Criteria for ENI were: Gleason sum 8-10, PSA >20 ng/ml, ≥cT3b or cN1. Fiducial markers (Visicoil®) were inserted into the prostate and an endorectal balloon filled with 100 120 cm 3 of air was used to stabilise the rectal position. Patients were asked to empty bladder and drink 500 ml of water 30 minutes before treatment. Daily intrafractional monitoring with Exactrac System and/or cone-beam CT was performed before and during each fraction. The dose for a urethral PRV with a 3 mm margin was limited to D5% ≤34.77 Gy and D2% ≤35.75 Gy. ADT was proposed for 24 months ± androgen receptor pathway inhibitor. All patients received an alpha-1 receptor antagonist one month before, during and one month after SBRT and dexamethasone 4 mg only on treatment days since 2021. Physician-reported morbidity was assessed using CTCAE v5. Results: With a median follow-up time of 29.3 months (range 1-51.7), 69 patientes are alive and one patient has died of sepsis. With the exception of two patients, one of whom had local and distant progression and the other nodal progression, disease control was achieved in all patients. One patient had a second pancreatic cancer. 45.7% of patients were treated with ENI, 20% received a lymph node boost. Tolerance was acceptable and the majority of patients had no side effects. There were no acute G3 and G4 side effects, only five patients had G3 late side effects, one genitourinary (GU), four gastrointestinal (GI) and one patient had a G4 late side effect in the form of a recto vesical fistula requiring urostomy and rectostomy (Figure 1).