A Prospective Phase 2 Trial of Transperineal Ultrasound-Guided Brachytherapy for Locally Recurrent Prostate Cancer After External Beam Radiation Therapy (NRG Oncology/RTOG-0526)

Purpose: Only retrospective data are available for low-dose-rate (LDR) salvage prostate brachytherapy for local recurrence after external beam radiation therapy (EBRT). The primary objective of this prospective phase 2 trial (NCT00450411) was to evaluate late gastrointestinal and genitourinary adverse events (AEs) after salvage LDR brachytherapy.

Methods And Materials: Eligible patients had low- or intermediate-risk prostate cancer before EBRT and biopsy-proven recurrence >30 months after EBRT, with prostate-specific antigen levels <10 ng/mL and no regional/distant disease. The primary endpoint was grade 3 or higher late treatment-related gastrointestinal or genitourinary AEs occurring 9 to 24 months after brachytherapy. These AEs were projected to be ≤10%, with ≥20% considered unacceptable. All events were graded with National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. Multivariate analyses investigated associations of pretreatment or treatment variables with AEs.

Results: One hundred patients from 20 centers were registered from May 2007 to January 2014. The 92 analyzable patients had a median follow-up of 54 months (range, 4-97) and a median age of 70 years (interquartile range [IQR], 65-74). The initial Gleason score was 7 in 48% of patients. The median dose of EBRT was 74 Gy (IQR, 70-76) at a median interval of 85 months previously (IQR, 60-119). Only 16% had androgen deprivation at study entry. Twelve patients (14%) had late grade 3 gastrointestinal/genitourinary AEs, with no treatment-related grade 4 or 5 AEs. No pretreatment variable predicted late AEs, including prior EBRT dose and elapsed interval. Higher V100 (percentage of prostate enclosed by prescription isodose) predicted both occurrence of late AEs (odds ratio, 1.24; 95% confidence interval, 1.02-1.52; P = .03) and earlier time to first occurrence (hazard ratio, 1.18; 95% CI, 1.03-1.34; P = .02).

Conclusions: This prospective multicenter trial reports outcomes of salvage LDR brachytherapy for post-EBRT recurrence. The rate of late grade 3 AEs did not exceed the unacceptable threshold. The only factor predictive of late AEs was implant dosimetry reflected by V100. Efficacy outcomes will be reported at a minimum of 5-year follow-up.