Long-term Data Show No Significant Difference Between PSA Control, OS After HDR-BT

Researchers from the United Kingdom evaluated long-term freedom from biochemical relapse (FFbR) and overall survival (OS) after single-dose high-dose-rate brachytherapy (HDR-BT) compared with 2- or 3-fraction schedules. They presented their new data at the American Society for Radiation Oncology 2023 Annual Meeting.

The study comprised 3 patient arms. Each patient had intermediate- or high-risk prostate cancer and received 1×19 Gy or 1×20 Gy (arm A=49), 2×13 Gy (arm B=138), or 3×10.5 Gy (arm C=106) as their sole treatment. Patients were staged with pelvic magnetic resonance imaging (MRI) and isotope bone scans.

Transperineal, transrectal ultrasound-guided implantation was followed by an MRI-based clinical target volumes definition based on the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology guidelines. Biochemical relapse was measured using the Phoenix definition (prostate-specific antigen [PSA] nadir plus 2 µg/L). Patients were evaluated prospectively from 6 months after implant and biannually thereafter. Estimates of FFbR and OS were calculated using the Kaplan-Meier (K-M) method and the log-rank test for significance. Univariate and multivariate hazard ratios (HRs) were obtained using Cox’s proportional hazard model, and a stepwise reduction method was used for multivariate modelling.

The median follow-up for arms A, B, and C, respectively, was 123, 116, and 120 months. Neoadjuvant and adjuvant androgen deprivation therapy (ADT) was administered to 80% of all patients, with a median duration of 9 months in arm A and 6 months in arms B and C. K-M estimates of FFbR at 8 and 10 years were 67% and 64% (arm A), 78% and 72% (arm B), and 80% and 76% (arm C), respectively.

Differences in FFbR between cohort arms were not significant (P=.2), and no significant difference was seen in OS. Eight- and 10-year estimates were 81% and 75% (arm A), 85% and 74% (arm B), and 90% and 83% (arm C), respectively (P=0.5). HRs for risk of biochemical recurrence were significant for ADT administration and overall risk category upon multivariate analysis, with the latter also significant in univariate analysis. Risk of death, Gleason risk (low, intermediate, high), MRI tumor stage risk, and overall risk category were significant in univariate analyses. Tumor stage and Gleason risk were also significant in multivariate analyses.

According to these new data, potential concerns surrounding the efficacy of 19-20 Gy single-dose HDR-BT as a monotherapy may be unfounded. Long-term outcomes data up to 10 years show no significant difference in PSA control and OS compared with 2 and 3 fractions of HDR-BT.