S1315
Clinical - Urology
ESTRO 2026
treatments were excluded. PSMA PET/CT findings were classified by prostate cancer molecular imaging standardized evaluation (PROMISE) score and stratified by D’Amico risk. Treatment decisions were extracted from clinical records. A non - parametric statistical analysis was employed (MedCalc® software). Results: Sixty patients were included (median age 79 years, IQR: 75-82). Median PSA value was 1.25 ng/ml (range 0.12-5.02), and median PSA doubling time was 11.8 months (range 0-87.9). The overall PSMA PET/CT detection rate was 71.7% (n=43/60). Of those with positive scans, 81% (n=35/43) were oligo - metastatic and 19% (n=8/43) were multi - metastatic. According to the PROMISE score, 10 (23%) patients had only local recurrence, 10 (23%) only pelvic lymph node disease, 10 (23%) only distant metastases, 13 (31%) had local and distant disease (both lymph nodes and bone metastases). By D’Amico risk classification, 83.9% (30/35) of unfavourable intermediate/high - risk patients had a positive PET, compared with 52.0% (13/25) of low/favourable intermediate - risk patients (chi squared, p<0.05). Follow - up data were available for 54 patients (90%). In 92.6% (n=50/54), PET findings guided therapy choice: 97% (n=38/39) of PET - positive patients received additional treatment (hormonal therapy, RT, or chemotherapy), whereas 80% (n=12/15) of PET - negative patients were managed with watchful waiting (chi-square, p<0.001). Conclusion: PSMA PET/CT detects PCa recurrence in about 72% of patients with PSA rises below Phoenix-threshold. By identifying disease at an earlier stage, many patients may become eligible for salvage or metastasis- directed therapies. Keywords: Prostate cancer, PSMA PET/CT, Phoenix criteria Prostate SBRT: updated efficacy and safety outcomes from a Chilean high volume center Gabriel Lazcano Álvarez 1,2 , Darlett Folch Mora 1 , Josefa Giusti-Bilz Schäfer 3 , Gonzalo Lanza Prüssing 3 , María José Maluk Alarcón 1 , Anaís Molina Cárcamo 3 , Francisco Pérez Peña 1 , Maximiliano Reyes Escobar 1 , Gabriel Veillon Contreras 1,2 , Tomás Walter Martin 1 , José Solís Campos 1,2 1 Oncology, Universidad de Valparaíso, Valparaíso, Chile. 2 Radiation Oncology, Hospital Carlos Van Buren, Valparaíso, Chile. 3 School of Medicine, Universidad de Valparaíso, Valparaíso, Chile Digital Poster 5000
Purpose/Objective: Stereotactic body radiation therapy (SBRT) is an emerging standard for localized prostate cancer. This study reports updated efficacy and adverse effects (AEs) data from patients treated at a public tertiary
high volume center. Material/Methods:
A retrospective, single-center cohort of patients treated between 2020 and early 2025 was analyzed. SBRT prescription was 36.25 Gy in 5 fractions to the prostate, with ≥ 85% of the CTV receiving 40 Gy. Seminal vesicles were excluded in low-risk cases and received 27.25 Gy to the proximal 1 cm and 2 cm in intermediate and high-risk groups, respectively. No pelvic nodes were irradiated.CT and 1.5 T T2-weighted MRI planning images were co-registered. No urethral catheters, fiducials, or rectal spacers were used. Treatment was delivered on a Versa HD LINAC (Elekta AB, Sweden) with a 6 MVFFF beam, requiring daily cone-beam CT verification and rectal/bladder preparation checks.Per local protocol, androgen deprivation therapy was indicated for intermediate- risk (6 months) and high-risk (18–36 months) disease.Clinical data were analyzed in STATA 19, reporting descriptive and Kaplan–Meier survival analyses. Biochemical failure followed Phoenix criteria. AEs were graded by RTOG for genitourinary (GU) and gastrointestinal (GI) domains. Patients required at least one PSA follow-up. Results: The cohort included 302 patients with a median follow-up of 21 months (IQR 12–35.9). Median age was 71 years (IQR 67–76); 97.3% ECOG 0–1; median IPSS 8 (IQR 5–15). Median PSA at diagnosis was 10.34 ng/mL (IQR 6.8–17). Risk distribution: 18.1% low, 39.9% intermediate, 42.0% high.At 36 months, biochemical control was 98.8% overall, 100% in low/intermediate and 97.5% in high-risk patients. Six failures occurred at 4, 27, 38, 42, 44, and 45 months (five in high-risk cases). Graded AEs:Acute GU: G0 48.3%, G1 41.7%, G2 8.6%, G3 0.3% (3 missing).Acute GI: G0 66.6%, G1 24.2%, G2 6.0%, G3 2.7% (2 missing).Late GU: G0 45.4%, G1 33.1%, G2 16.6%, G3 1.7%, G4 0.3% (9 missing).Late GI: G0 68.9%, G1 22.2%, G2 5.3%, G3 0.7% (9 missing).
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