Biochemical outcomes after prostate brachytherapy with 5-year minimal follow-up: Importance of patient selection and implant quality

Abstract Purpose A prostate brachytherapy program was initiated in 1990, when comparatively little was known of the relative importance of disease- and treatment-related factors on outcome. Patients treated during the first 6 years of the program were analyzed to determine the value of patient selection and implant quality on biochemical control. Methods and materials We treated 243 patients with clinically localized prostate cancer with radioactive seed implantation and underwent 1-month CT-based dosimetric analysis. Follow-up ranged from 61 to 135 months (median 75). The Gleason score was ≤6 in 78% ( n = 189), 7 in 14% ( n = 35), and 8–10 in 8% ( n = 19). The initial prostate-specific antigen (PSA) level was ≤10 ng/mL in 61% ( n = 149), 10.1–20 ng/mL in 26% ( n = 63), and >20 ng/mL in 13% ( n = 31). The disease stage was T2a or less in 49% ( n = 120), and Stage T2b-T2c in 51% ( n = 123). A real-time ultrasound-guided technique was used with 125 I ( n = 138) and 103 Pd ( n = 105) isotopes. No patient underwent external beam radiotherapy as part of their primary treatment. Of the 243 patients, 60% also received hormonal ablation for at least 3 months before and 2–3 months after seed implantation. All patients included underwent a 1-month CT-based dosimetric analysis. The implant dose was defined as the dose delivered to 90% of the prostate volume on postimplant dosimetry (D 90 ). On the basis of prior dose–response analyses, patients were retrospectively grouped into optimal D 90 ( 125 I ≥140 Gy Task Group 43 or 103 Pd ≥100 Gy) and suboptimal D 90 ( 125 I 103 Pd Results Disease-related factors, including initial PSA level, Gleason score, and stage, were significant predictors of biochemical failure. The actuarial 8-year freedom from biochemical failure (bFFF) rate was 80% for those with a PSA level ≤10 ng/mL, 86% for PSA 10.1–20 ng/mL, and 45% for PSA >20 ng/mL ( p = 0.0019). Patients with a Gleason score of ≤6 had an 8-year bFFF rate of 81% vs. 67% for those with Gleason score 7 and 53% for those with Gleason score 8–10 ( p = 0.0003). Patients with Stage T2a or less had an 8-year bFFF rate of 85% compared with 69% for those with Stage T2b-T2c ( p = 0.013). The 8-year bFFF rate was 88% for low-risk patients (Stage T2a or less, Gleason score ≤6, and initial PSA level ≤10 ng/mL; n = 75), 81% for moderate-risk patients (Stage T2b or Gleason score 7 or initial PSA level >10.1–20 ng/mL; n = 70), and 65% for high-risk patients (two or more moderate-risk features or Gleason score ≥8 or initial PSA level >20 ng/mL; n = 98; p = 0.0009). Patients with optimal dose implants ( n = 145) had an 8-year bFFF rate of 82% compared with 68% for those with suboptimal dose implants ( n = 98; p = 0.007). Hormonal therapy did not significantly affect biochemical failure ( p = 0.27). In multivariate analysis, the statistically significant variables included initial PSA level ( p p = 0.024), and dose group ( p = 0.046). Because our current practice limits implantation alone to low-risk patients, an analysis of this subgroup was undertaken to validate the importance of dose. In the optimal dose group, low-risk patients had an 8-year bFFF rate of 94% vs. 75% for the low-risk patients in the suboptimal dose group ( p = 0.02). Conclusion With minimal follow-up of 5 years, these data continue to support the use of implantation alone in low-risk prostate cancer patients and demonstrate the importance of implant quality (dose) in achieving optimal outcomes. Low-risk patients who receive an optimal dose implant have a 94% bFFF rate at 8 years.