S1165
Clinical - Urology
ESTRO 2026
Digital Poster 1056 LDR brachytherapy versus SBRT for low- and favorable-intermediate risk prostate cancer: ten- year oncological outcomes and toxicity María Cerrolaza 1 , Agustina Mendez 1 , Cristina García 1 , Maria del Mar Puertas 1 , Victoria Navarro 2 , Claudia Colom 1 , Ana Galan 1 , Claudia Laborda 1 , Andrea Ochoa 1 , Javier Diez 3 , Pablo Alares 4 , Reyes Ibañez 1 1 Radiation Oncology, Miguel Servet University Hospital, Zaragoza, Spain. 2 Radiation Oncology, Lozano Blesa University Clinical Hospital, Zaragoza, Spain. 3 Department of Physics, Miguel Servet University Hospital, Zaragoza, Spain. 4 External Consultant, in collaboration with the Department of Radiation Oncology, Miguel Servet University Hospital, Zaragoza, Spain Purpose/Objective: Low-dose-rate (LDR) brachytherapy and stereotactic body radiotherapy (SBRT) are both established treatment options for early localized prostate cancer. However, few studies have directly compared their long-term efficacy and toxicity. This study aims to evaluate and compare oncologic outcomes and toxicity between LDR brachytherapy and SBRT in this population. Material/Methods: Patients with low- and favorable-intermediate risk prostate cancer treated with LDR brachytherapy (BQT) or stereotactic body radiation therapy (SBRT) (35 Gy in 5 fractions) between January 2015 and December 2016 were included. Biochemical recurrence was defined by the Phoenix criterion, and toxicity by CTCAE v5.0. Follow-up included PSA and IPSS evaluation every six months. Group comparisons used χ² and Student’s t tests; biochemical control was estimated by Kaplan– Meier, with p < 0.05 considered significant. Results: A total of 136 patients were included, 61 treated with BQT and 75 with SBRT, with an overall median follow- up of 9.6 years. The mean age was 67.5 years for BQT and 70.3 years for SBRT (p = 0.023). Baseline PSA was significantly higher in SBRT patients (8.87ng/mL) compared to BQT (7.45 ng/mL; p = 0.017). ISUP grade distribution differed significantly (p = 0.001), with a higher proportion of ISUP 2 tumors observed in SBRT patients. Androgen deprivation therapy was more frequently used in SBRT (38.7%) than BQT (16.4%; p = 0.004). Pre-treatment IPSS scores were comparable (BQT 7.39, SBRT 8.65).Post-treatment, BQT patients showed a greater increase in IPSS, with significant differences at 1, 3, and 6 months, indicating higher early urinary toxicity.Severe late urinary and rectal toxicity ( ≥ G3) was more frequent after BQT (27.9% and 9.8%, respectively) than after SBRT (6.7% and 4.0%; both p < 0.001). Biochemical recurrence
low prevalence of Grade >1 side effects, the analysis was made based on the presence of side effects, independently of its Grade. For acute GU side effects, the best correlation was found for Bladder V%10Gy (p=0.07).
For chronic GU side effects, several variables showed significance in a logistic regression fit (Table 1). Only urethra and urethra PRV (urethra+2mm) showed significance with chronic GU side effects in higher dose levels. Regarding the target organs, both PTV and prostate showed a correlation between higher doses and the presence of side effects. It is worth commenting the effect of PTV coverage in dose levels of 34Gy and 35Gy. They suggest that, the lower the coverage, the higher the incidence of side effects. This occurs as V%34Gy and V%35Gy are inversely correlated to V%38Gy and V%39Gy (Figure 1).
Conclusion: A correlation between high dose levels in prostate, PTV and urethra (with or without PRV) and chronic GU side effects was found. An inverse correlation was found between V34Gy and V35 levels and chronic GU side effects. From the treatment planning point of view, results suggest that an effort for higher conformity leads to a higher inhomogeneity in the PTV, causing a higher chance of chronic GU toxicity. Keywords: Prostate SBRT, Cyberknife, GU side effects
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