Impact of supplemental external beam radiotherapy and/or androgen deprivation therapy on biochemical outcome after permanent prostate brachytherapy

Abstract 

Purpose

To evaluate the impact of supplemental external beam radiotherapy (EBRT) and/or androgen deprivation therapy (ADT) on 8-year biochemical outcome after permanent prostate brachytherapy.

Methods and materials

Between April 1995 and January 2001, 668 consecutive patients underwent brachytherapy using either ¹⁰³Pd or ¹²⁵I for clinical Stage T1b–T3aNxM0 (2002 American Joint Committee on Cancer) adenocarcinoma of the prostate gland. No patient underwent seminal vesicle biopsy or pathologic lymph node staging. The median follow-up was 58.6 months. Biochemical progression-free survival was defined by the American Society for Therapeutic Radiology and Oncology consensus definition. The clinical, treatment, and dosimetric parameters evaluated for biochemical progression-free survival included supplemental EBRT, ADT, patient age, clinical stage, Gleason score, preimplant prostate specific antigen (PSA), risk group, percentage of positive biopsies, isotope used, prostate volume, planning volume, percentage of target volume receiving 100%, 150%, and 200% of prescribed dose, minimal percentage of dose covering 90% of target volume, tobacco status, hypertension, and diabetes.

Results

For the entire group, the actuarial 8-year biochemical progression-free survival rate was 98.2%, 98.4%, and 88.2% for low-, intermediate-, and high-risk patients, respectively, with a median PSA level of <0.1 ng/mL for all risk groups and ADT and EBRT subgroups. At last follow-up, only 5 patients (0.8%) had died of metastatic prostate cancer. In multivariate analysis, Gleason score, percentage of positive biopsies, and ADT predicted for biochemical outcome in high-risk patients. In low- and intermediate-risk patients, none of the evaluated variables predicted for biochemical outcome. For the entire population, pretreatment PSA level, Gleason score, ADT, and clinical stage predicted for 8-year biochemical progression-free survival, with the percentage of positive biopsies approaching statistical significance.

Conclusion

Prostate brachytherapy results in a high probability of 8-year biochemical progression-free survival for low-, intermediate-, and high-risk patients. Although the role of supplemental EBRT could not be adequately evaluated in high-risk patients, it did not improve biochemical outcome in low- and intermediate-risk patients. However, ADT resulted in a statistically significant improvement in progression-free survival for high-risk patients.

Keywords:  Prostate cancer, Brachytherapy, Biochemical outcome, ¹⁰³Pd, ¹²⁵I