Primary Analysis of (NCT03380806) a Phase II Randomized Trial of Stereotactic Body Radiotherapy Boost Versus Conventional Fractionation External Beam Radiotherapy Boost in Unfavorable‐Intermediate and High‐Risk Prostate Cancer

BACKGROUND: Standard treatment for unfavorable-intermediate and high-risk prostate cancer involves androgen deprivation therapy (ADT) in combination with pelvic conventional fractionation (CF) external beam radiotherapy (EBRT) and a CF-EBRT or brachytherapy boost to the prostate. This trial compared CF-EBRT boost with stereotactic body radiotherapy (SBRT) boost after pelvic CF-EBRT. METHODS: Patients were randomized to receive a boost using either CF-EBRT (32-34 Gy in 15-17 fractions) or SBRT (19.5-21 Gy in three weekly fractions) following pelvic CF-EBRT (45-46 Gy in 23-25 fractions). The primary objective was to assess early (3-month post-radiotherapy) gastrointestinal (GI) and genitourinary (GU) quality of life (QoL), using the expanded prostate index composite (EPIC) score. Secondary objectives included long-term QoL, International Prostate Symptom Score (IPSS) changes, toxicity assessments, and long-term disease control outcomes. Linear regression and Fisher's exact test were used for analysis. RESULTS: Of the 100 patients randomized, 53 received CF-EBRT, and 47 received SBRT. After a mean follow-up of 18.5 months, no significant differences were observed in EPIC score changes between CF-EBRT and SBRT at 3 months posttreatment for urinary (11.5 vs. 8.6, p = 0.23), bowel (5.2 vs. 6.4, p = 0.57), and overall QoL (8.3 vs. 7.5, p = 0.61). IPSS scores were similar (p = 0.11), and CTCAE v.5.0 toxicity rates were comparable, with an odds ratio of 0.90 (p > 0.99). Biochemical failure rates were under 5% for both groups. CONCLUSIONS: This is the first randomized trial to report QoL outcomes after SBRT boost radiotherapy in patients with unfavorable-intermediate and high-risk prostate cancer. SBRT boost after pelvic CF-EBRT is well-tolerated and demonstrates comparable outcomes in QoL and toxicity to the CF-EBRT boost. Further follow-up is needed to assess the long-term effects on QoL, toxicity, and disease control. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03380806.