Long-Term Outcomes of Low Dose Rate Prostate Brachytherapy at a Single Institution

Abstract

To report long-term oncologic outcomes for 441 men treated with Iodine-125 or Palladium-103 low dose rate prostate brachytherapy (LDR-BT) at a single institution. A total of 441 men, median age 70 years, were treated with either Iodine-125 (37%) or Palladium-103 (63%) LDR-BT for low, intermediate or high-risk prostate cancer as stratified by D'Amico criteria, between March 1997 and July 2008. Mean prostate-specific antigen (PSA) level was 7.66 ng/ml (SD 5.1). T stage was cT1c in 54% and cT2 in 45% of patients. Gleason score was 6 in 67%, 7 in 28%, or 8-10 in 5% of patients. A 3-6 month neoadjuvant androgen deprivation therapy (ADT) course was used in 32% of patients primarily for prostate gland downsizing to <65cc. External beam radiation therapy (EBRT) to 4500 cGy in 25 fractions combined with LDR-BT was used in 43.7% (n = 191) of patients. Post-implant dosimetry was done 30 days after implantation with doses converted to the biologically effective dose (BED). Statistical analyses including Kaplan-Meier curves, Wilcoxon signed-rank and Chi square tests were performed. There was no significant difference in biochemical recurrence or prostate cancer specific survival based on initial PSA, LDR-BT isotope, EBRT, or ADT use. Median follow-up and inter-quartile (Q1-Q3) follow-up was 92 (65-130) months respectively. There were 55 failures (12% of the cohort), as defined by the ASTRO guidelines for biochemical recurrence with median time to recurrence and (Q1-Q3) of 58 (25-90) months. A total of 67 deaths occurred, with only 8 deaths from prostate cancer, at a median of 116 (72-130) months. Overall survival was 83% with prostate cancer specific survival at 98.3% overall, 99.6% for low-risk, 97.6% for intermediate-risk, and 88.9% for high-risk patients, with a median follow up of 92 (70-136) months. Kaplan-Meier analysis showed the difference of prostate cancer free survival between the risk groups to be statistically significant (p < 0.01). When D90 (the radiation dose delivered to 90% of the prostate) was less than 160% of the prescription dose, PSA control was 84%, but when D90 was > or =160%, PSA control was 92%. All failures in the cohort never experienced reduction of PSA to < 2.0 ng/ml after LDR-BT, which suggests that occult metastatic disease may have been present at the time of treatment. Iodine-125 and/or Palladium-103 LDR-BT either as monotherapy or in combination with ADT and/or EBRT is a highly effective treatment option for prostate cancer and yields excellent long-term oncologic outcomes comparable to other modalities.