Distant Metastases Following Permenanet Interstitial Brachytherapy for Patients With Clinically Localized Prostate Cancer

Abstract

Purpose: Recent publications have suggested high risk patients undergoing radical prostatectomy have a lower risk of distant metastases and improved cause-specific survival than patients receiving definitive external beam radiation therapy. To date, none of these studies have compared distant metastases and cause-specific survival in brachytherapy patients including those with high risk features. In this study, we evaluate such parameters in a consecutive cohort of patients undergoing permanent interstitial brachytherapy. Materials and Methods: Between April 1995 and June 2007, 1,840 consecutive patients with clinically localized prostate cancer were treated with permanent interstitial brachytherapy. Risk group stratification was as per NCCN guidelines. Six hundred fifty eight, 893 and 289 were assigned to low, intermediate and high risk categories. Median followup was 7.4 years. Biochemical progression-free survival was defined as a PSA ≤0.40 ng/mL after nadir. The median day 0 D90 for all patients was 119.2% of prescription dose. Nine hundred thirty nine patients (51.0%) received supplemental external beam radiation therapy and 670 (36.4%) received androgen deprivation therapy (median duration 4 months). The mode of failure (biochemical, local or distant) was determined for each failed patient. Cause of death was determined for each deceased patient. Patients with metastatic prostate cancer or castrate resistant disease without obvious metastases who died of any cause were classified as dead of prostate cancer. Multiple clinical, treatment and dosimetric parameters were evaluated for impact on outcome. Results: For the entire cohort, metastases-free and cause-specific survival at 12 years were 98.1% and 98.2%, respectively. When stratified by low, intermediate and high risk groups, the 12-year metastasis-free survival was 99.8%, 98.1% and 93.8% (p < 0.001), respectively. At 12 years cause-specific survival was 99.8%, 98.0% and 95.3% (p < 0.001) for low, intermediate and high risk groups. Biochemical progression-free survival at 12 years was 98.7%, 95.9% and 89.4% for low, intermediate and high risk patients (p < 0.001). In multivariate Cox-regression analysis, metastases-free survival was mostly closely related to Gleason score, while biochemical progression-free survival was associated with Gleason score and year of treatment. Cause- specific survival was most closely related to Gleason score. For biochemically controlled patients, the median post-treatment PSA was <0.02 ng/mL. Conclusions: Excellent cause-specific and metastases free survival are achievable with high quality brachytherapy for low, intermediate and high risk patients. These results compare favorably to alternative treatment modalities including radical prostatectomy. In particular, our metastases free survival and cause-specific survival for high risk patients appear superior to published radical prostatectomy and external beam radiation therapy series.