ESTRO 2025 - Abstract Book

S1952

Clinical - Urology

ESTRO 2025

References: 1. Brand, D. H. et al. Intensity-modulated fractionated radiotherapy versus SBRT for prostate cancer. The Lancet Oncology, 2019. 2. Widmark, A. et al. Ultra-hypofractionated versus conventionally fractionated radiotherapy for prostate cancer. The Lancet, 2019. 3. Murthy, V. et al. Prostate-Only Versus Whole-Pelvic Radiation Therapy in High-Risk and Very High-Risk Prostate Cancer. JCO, 2021. 4. Murthy, V. et al. Study protocol of a randomised controlled trial of prostate radiotherapy in high-risk and node positive disease comparing moderate and extreme hypofractionation. BMJ, 2020. 5. Sanguineti. et al. Comparison of three strategies to delineate the bowel for whole pelvis IMRT of prostate cancer. Radiotherapy and Oncology, 2008. Digital Poster Apalutamide, ADT and stereotactic radiotherapy (AD ASTRA) phase II study in high-risk prostate cancer: study design and preliminary safety analysis Pavol Dubinský 1,2 , Miroslav Olejár 1 , Katarína Belánová 1 , Natália Janíčková 1 1 Department of Radiation Oncology, East Slovakia Institute of Oncology, Kosice, Slovakia. 2 Faculty of Health, Catholic University, Ruzomberok, Slovakia Purpose/Objective: In high-risk prostate cancer (PCa), primary radiotherapy (RT) treatment outcomes might be improved by long-term androgen deprivation (ADT) 1 , addition of an androgen receptor pathway inhibitor 2 , RT dose escalation 3 , and pelvic nodal irradiation (PNI) 4 . We hypothesized that the combination of apalutamide with ADT and radiobiologically dose escalated ultra-hypofractionated prostate and pelvic SBRT would be well tolerated and effective. Material/Methods: Investigator-initiated phase II study AD ASTRA combines 18-month administration of daily apalutamide 240 mg with ADT and prostate and pelvic SBRT. Eligible men have biopsy-confirmed EAU high-risk localized or locally advanced PCa and are in ECOG PS 0- 1 with modified Charlson comorbidity index ≤4. Staging is based on digital rectal examination and conventional imaging with mandatory pelvic mpMRI and optional 68GaPSMA-PET/CT, which is mandatory at PSA progression. Total RT dose is 36.25 Gy to the prostate, 35 Gy to involved nodes, and 25 Gy to PNI volume in 5 fractions on alternate days during month 3. Target volumes are irradiated simultaneously with rigid prostate fiducial markers registration and intrafraction prostate motion control. Patients are assessed for toxicity with CTCAE v.5, and patient-reported outcomes questionaries. The primary study endpoint is 5-year biochemical control rate. Enrolment started in July 2023 with the goal of 43 patients. We performed preliminary safety analysis in the first 20 patients seen on month 5 visit. The trial is registered with EU CT Number: 2024-517901-97-00. Results: Mean age was 65 years (47-74 years). Five (25%) and 15 (75%) men were assigned to either localized or locally advanced high-risk category, respectively. Mean PSA was 29.6 ng/ml (7.5-84.2ng/ml), ISUP Grade 4 or 5 was present in 65%, cT3/4 in 50% and cN1 in 25%. All patients were irradiated as planned and remained on ADT and apalutamide except for the reduction to 180 mg of apalutamide in 1 patient. Acute gastrointestinal toxicity G1 and G2 was observed in 50% and 25%, acute genitourinary toxicity G1 and G2 in 40% and 20% respectively, and no G3. Adverse events of special interest included G3 fall in 1 patient, both G2 and G3 hypertension in 1, G2 transitory ischemic attack in 1, G1 and G2 skin rash in 2 and 1 respectively, and G1 hypothyroidism in 1. 1575