(OA19) Low-Dose-Rate Brachytherapy as Monotherapy for High-Risk Prostate Cancer: 15-Year Outcomes Data

Abstract

Currently available randomized data suggest favorable outcomes for high-risk prostate cancer (HRPC) patients treated with external beam radiotherapy (EBRT) and brachytherapy in conjunction with hormonal therapy (HT). However, in certain clinical scenarios patients may not be suitable for EBRT, in which case radiation oncologist is tasked with a challenging decision with regards to disease management. In this study we aimed to examine long-term biochemical control and survival with low-dose-rate brachytherapy (LDR-BT) alone for HRPC. 504 patients with NCCN HRPC were treated with LDR-BT and/or EBRT in our institution in the period 1990-2015. Among these patients, 66 (13%) received LDR-BT alone, and were the subjects of the primary analysis. 419 (83%) patients, treated with combined modality (EBRT plus LDR-BT), were included in the secondary, comparative, analysis. Biochemical failure-free survival (BFFS), distant metastases-free survival (DMFS), prostate cancer-specific survival (PCSS), and overall survival (OS) were selected as study endpoints. Survival was examined using the log-rank test, Kaplan-Meier method, and Cox regression modeling. The median age at diagnosis for all patients was 69 years. Stage ≥T3a represented 2% patients in monotherapy cohort versus 14% in combined cohort (p=0.01), Gleason Score (GS) >7 - 43% versus 72% (p<0.0001), and PSA >20 - 65% versus 34% (p<0.0001), respectively. HT was administered to 58% men treated with LDR-BT alone versus 97% - with combined modality (p<0.0001). Among patients in the monotherapy cohort, median follow-up was 9.6 years. A total of 38 (58%) deaths were recorded. 14 (21%) patients died of prostate cancer, 5 (8%) developed distant metastases, and 34 (52%) - biochemical failure. The 10- and 15-year BFFS rates were 40% and 37% for monotherapy versus 73% and 68% for combined modality (p<0.00001). The 10- and 15-year DMFS rates were 93% and 90% for monotherapy versus 88% and 78% for combined modality (p=0.33). The 10- and 15-year PCSS rates were 88% and 79% for monotherapy versus 89% and 83% for combined modality (p=0.56). Finally, the 10- and 15-year OS rates were 78% and 45% for monotherapy vs 70% and 49% for combined modality (p=0.66). For patients treated with LDR-BT alone, BFFS was better with receipt of HT: 65% versus 16% at 10 years (p<0.00001), whereas OS and PCSS were not affected by HT. On multivariate analyses for the monotherapy cohort, Gleason Score >7 (HR 3.42, p=0.02), PSA 10-20 (HR 5.93, p=0.02), and PSA >20 (HR 7.76, p=0.01) were associated with worse BFFS. Receipt of HT receipt predicted better BFFS (HR 0.36, p=0.01), but not OS (HR 1.29, p=0.53). In the present HRPC analysis, patients treated with brachytherapy alone had a more favorable disease with respect to stage and GS, but not PSA, as compared with those treated with combined modality. In this context, LDR-BT monotherapy yielded an inferior long-term biochemical control, although DMFS and PCSS were comparable with combined regimen. Select patients with life expectancy <10 years who are unable to receive EBRT may be considered for LDR-BT alone with HT.