Biochemical outcomes for patients with intermediate-risk, organ-confined prostate cancer treated with I-125 interstitial brachytherapy monotherapy.

Abstract

192 Background: Treatment with low dose rate brachytherapy (LDR-BT) monotherapy is well established for low risk prostate cancer. The routine use of LDR-BT in intermediate risk (IR) is more controversial and is often combined with additional external beam radiotherapy (EBXRT). We report the biochemical outcome of a large cohort of patients with IR disease treated with LDR-BT monotherapy. Methods: A multi-institutional prospective database identified 615 patients with IR prostate cancer treated with I-125 interstitial BT between 2003–2007. IR was defined using Memorial Sloan-Kettering Cancer Centre (MSKCC) definition of either T2b, or Gleason score (GS) 7 or raised initial PSA (iPSA) 10.1-20ng/ml. Patients receiving additional EBXRT were excluded. Biochemical failure was defined by both ASTRO (3 rises past nadir) and Phoenix criteria (nadir plus 2). Kaplan-Meier methods were used to estimate biochemical no evidence of disease rates (bNED) and univariate analyses used to identify potential prognostic factors. Results: The median age was 64 years (range 49–82). Forty-three patients had stage T2b, 180 had iPSA 10.1-20 and 392 had GS 7 disease. Only 108 received androgen deprivation therapy (ADT) prior to implant. Median follow up was 5.0 years. The 5-year bNED rates (95% confidence interval) by ASTRO are 85.5% (82.0–88.3%) and for Phoenix 83.7% (80.0–86.7%). Use of ADT, GS 3+4 versus 4+3, and dosimetric indices were not significant prognostic variables. When stratified by risk factor (T2b, GS7 or raised iPSA) raised iPSA correlated to poorer outcome only by Phoenix criteria (by Phoenix p=0.001, by ASTRO p=0.311). Conclusions: We have demonstrated good biochemical control for IR patients treated with LDR-BT alone. No additional benefit was seen with the use of ADT. We believe LDR-BT alone is an effective treatment option in selected IR prostate cancer patients with comparable outcome to other treatment modalities such as surgery or EBXRT.