1. Introduction/Aims There is less written about failure patterns after prostate brachytherapy (BT) alone or in combination with external beam radiotherapy (EBRT) for localized prostate cancer. To analyze patterns of failure following biochemical failure for prostate cancer patients treated with I-125 BT with or without supplemental EBRT (not to pelvis) with or without neoadjuvant androgen deprivative therapy (NADT). #1240 Patterns of Failure Following Biochemical Failure in 1311 Prostate Cancer Patients Treated with Brachytherapy with/without External Beam Radiation Therapy A. Yorozu, S. Saito, K. Toya, Y. Shiraishi, N. Kuroiwa, A. Takahashi, Y. Yagi, T. Nishiyama, T. Tanaka, Y. Shinya, Dept. of Radiation Oncology & Urology, Tokyo Medical Center, National Hospital Organization, Tokyo, Japan

2. Patients & Methods 1311 men with prostate cancer received I-125 BT from 2003 to 2009. We analyzed patterns of failure comprehensively, including 83 men with definitive biochemical failure according to Phoenix definition. Risk groups according to the NCCN guidelines; – Low-risk; 460, Intermediate-risk; 704, High-risk; 147 48% of men received supplemental EBRT to the prostate & seminal vesicles: 40% received NADT (median 8 months). Local failure was defined as a positive post-treatment biopsy (95%) and/or imaging consistent with failure in the prostate or seminal vesicles. First failure site was defined as the earliest anatomic relapse site. Anatomic relapse patterns were classified as a local, pelvic nodal, and distant pattern. The pattern was unable to be determined in 4 (5%).

3. Results: Failure patterns according to risk group Local failure High risk 3.9% at 7-yr Intermediate risk 1.7% Low risk 1.3% P=0.031 Nodal failure High risk 6.8% Intermediate risk 1.1% Low risk 0.0% P=0.009 Distant failure High risk 8.6% Intermediate risk 3.8% Low risk 1.0% P<0.001 LocalNodalDistant BED*Risk group NADTT stage NADT Predictive factors for failure patterns on multivariate analysis BED*: biologically effective dose (α/β=2Gy)

4. Conclusions Local failure BED <180 Gy2 4.8% at 7 yr BED ≥180 Gy2 1.2% p=0.002