PSOR11 Presentation Time: 12:20 PM: Long-Term Experience with Pd-103 Prostate Brachytherapy

Abstract

<h3>Purpose</h3> Although long-term control rates after low dose-rate brachytherapy are available, the majority of such series report patients treated with I-125 or Cs-131, whereas relatively fewer series have reported long-term results with Pd-103. We herein report our long-term experience using Pd-103. <h3>Materials and Methods</h3> Patients were treated with Pd-103 brachytherapy, either monotherapy or as boost with external beam. bRFS was defined as interval from implant date to biochemical failure using Phoenix criteria, while MFS was defined as the interval from implant to development of radiographic evidence of extraprostatic disease or death from any cause. Cox proportional hazards models were constructed with NCCN risk stratification. We also performed a preliminary dosimetric analysis of prostate D90 and V100 (Day 1) to assess implant quality as a predictive factor for bRFS and MFS. <h3>Results</h3> 495 patients treated between 2004-2019 consisted of 53 very-low, 218 low, 177 intermediate (119 favorable, 58 unfavorable), 32 high, and 15 very high-risk patients; the majority of patients with high-risk disease were treated in the period following ASCENDE-RT. One hundred twenty (24.2%) patients received external beam radiation (EBRT); 197 (39.8%) patients received androgen deprivation therapy. Median follow-up was 4.75 years, (0.1- 16.6 years); 168 (34%) of patients had ≥7 years of follow-up. Overall, biochemical relapse occurred in 32 (6.4%) of patients. At 5, 7, and 10 years post-implant, biochemical control rates (95% confidence) were 93.9% [91.5-96.3%], 93% [90.3-95.7%], and 90% [85.9-94.3%], respectively. Similarly, at 5, 7, and 10- years post-implant, 96.4% [94.3-98.5%], 94% [91.1-96.9%], and 88.7% [84.1-93.6%] of patients were free of metastatic disease or death. Among 9 patients with clinical relapse, 5 patients (1.0%) had pelvic nodal involvement and 4 (0.8%) had distant metastatic disease. With regard to metastases and death, high-risk prostate cancer was significantly associated with worse MFS, HR = 5.69 [1.58-20.5] (multivariate) and bRFS, HR = 3.43 [1.10-10.7]. Median MFS in the high-risk group was 13.7 years post-implant; median bRFS was 8.45 years. Low- and intermediate-risk patients had >80% freedom from metastases and all-cause death at 10 years, p = 0.03. Both low- and intermediate-risk patients had similarly excellent survival after brachytherapy, p = 0.3 (bRFS) and p = 0.11 (MFS). Overall, prostate D90 or V100 were not significantly associated with bRFS or MFS, p > 0.3. However, overall implant quality was high, with a median D90 of 112.7% [102.9-124.4]. <h3>Conclusions</h3> Brachytherapy with Pd¹⁰³ results in excellent long-term biochemical and local control at 5, 7, and 10 years. Dosimetry indicators were not significant predictors in this cohort, presumably because implant quality was consistently high.