1004 - Stereotactic Body Radiation Therapy (SBRT) Combined with Pelvic Radiotherapy and GTV Boost Based on Multiparameter Magnetic Resonance Image for High-Risk Prostate Cancer: A Phase II Study

S. Wang¹, J. Yao², H. Zeng³, X. Wang⁴, and O. Yan⁵; ¹Department of Radiation Oncology, Division of Abdominal Tumor Multimodality Treatment, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan, China, ²Department of Radiology, West China Hospital, Sichuan University, Chengdu, China, ³Department of Urology Surgery, West China Hospital, Sichuan University, Chengdu, China, ⁴Department of RadiationOncology, Division of Abdominal Tumor Multimodality Treatment, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan, China, ⁵Hunan Cancer Hospital and The Affiliated Cancer Hospital of Xiangya School of Medicine, Central South University, Changsha, China

Purpose/Objective(s): For low to intermediate-risk prostate cancer, the efficacy and safety of SBRT have been confirmed. However, the specific methods, efficacy, and safety of SBRT for high-risk prostate cancer require further exploration. This study aims to investigate the efficacy and safety of SBRT combined with pelvic radiation therapy and primary gross tumor volumes (GTVp) boost for high-risk prostate cancer. Materials/

Methods: This study is a prospective, single-arm, Phase II clinical study. High-risk prostate cancer patients (T3a or Gleason score = 8 or PSA > 20ng/mL) meeting the criteria were enrolled. Long-term Androgen deprivation therapy (ADT) was given for 2 to 3 years. Neoadjuvant ADT < 6 months was allowed. Before irradiation, all patients underwent multiparametric magnetic resonance imaging(mpMRI) for localization and delineation of the primary GTVp. The prostate and proximal seminal vesicles were considered clinical target volume (CTV) 1. The pelvic lymphatic drainage area constituted CTV2. The prescribed radiation doses for planning target volume of the primary tumor were 40 Gy or 45 Gy/5 fractions, while the doses for the prostate, seminal vesicles, and positive pelvic lymph nodes were 37.5 Gy/5 fractions, and the pelvic synchronous radiation dose was 25 Gy/5 fractions. Radiotherapy was delivered 3 times per week. The primary endpoint was biochemical recurrence-free survival, and secondary endpoints included overall survival (OS), toxicity (measured using Common Terminology Criteria for Adverse Events (CTCAE) v4.0), and quality of life (QLQ-C30 and IPSS).
Results: A total of 60 patients were enrolled from 2021 to 2023, with an average age of 76 years. The median follow-up time was 13.5 months. The biochemical recurrence-free survival rates are 96.7% at 6 months and 95% at 1 year. The 1-year overall survival rate at the last follow-up was 100%. At 3 months after radiotherapy, the proportion of PSA < 0.006ng/mL was 50%. The incidence of acute grade 1 GU toxicity was 78.3%; the incidence of acute grade 1 GI toxicity was 53.3%, with no acute grade 2 or higher toxicity observed. No grade 3 or higher late GU or GI toxicities were observed.
Conclusion: These preliminary results suggest that SBRT combined with pelvic radiotherapy and GTVp boost based on mpMRI for high-risk prostate cancer is effective and safe. Larger-scale multicenter randomized controlled trials are needed in the future to validate these preliminary results.