(P017) Long-Term Biochemical Progression-Free Survival and Quality-of-Life Outcomes in a Single-Institution Cohort of Prostate Cancer Patients Treated by Real-Time Inversely Optimized Prostate Seed Implantation

Eric Kemmerer, MD, Abhirup Sarkar, MS, James Martelli-Raben, Tate Muratori-Levit, Hungcheng Chen, MS, Firas Mourtada, PhD, Adam Raben, MD; Department of Radiation Oncology, Drexel University; Department of Radiation Oncology, Christiana Care

PURPOSE: Inversely optimized low-dose-rate prostate seed implantation (IO-PSI) has been shown to offer excellent biochemical progression–free survival (bPFS), with a favorable toxicity profile. Here, we report 9-year outcomes in patients with low-risk or intermediate-risk (IR) prostate cancer and examine for correlates of biochemical control and genitourinary quality-of-life (GU-QOL) outcomes.

METHODS: From 2003–2015, a total of 492 patients were identified who had received real-time IO-PSI as definitive treatment for prostate cancer, 353 with at least 2 years of follow-up. The median pretreatment prostate-specific antigen level was 5.1; median dose was 145 Gy (96% via ¹²⁵I); 91% were T1c; and 74%, 21%, and 4% had low-risk, favorable IR, and unfavorable IR disease, respectively. Seven percent received short-term androgen deprivation (SAD). Four patients had high-risk prostate cancer and were excluded from the survival analysis (Kaplan-Meier analysis with log-rank testing) for n = 349 patients. Cox proportional hazards and multivariable regression were performed to examine the relationship of clinical and dosimetric variables with bPFS and GU-QOL. ANOVA (analysis of variance) was used to compare dosimetry by risk group (P < .05).

RESULTS: At a median follow-up of 40 months, the overall 9-year bPFS was 92%, with 95%, 83%, and 75% in the low-risk, favorable IR, and unfavorable IR groups, respectively (P = .0002). Outcomes for men with Gleason 3/4 and 4/3 bPFS did not differ (P = .92). No significant difference in dosimetry among risk groups was observed. On Cox proportional hazards analysis, only risk group correlated with bPFS (P = .001). On multivariable analysis, postimplant V150% correlated with GU-QOL score (P = .0009). Crude incidences of grade ≥ 2 GU and gastrointestinal (GI) toxicities were 25% and 1%, respectively. No benefit to SAD was observed.

CONCLUSION: Overall, IO-PSI, resulting in reduced needle and source exposure, demonstrates excellent, durable bPFS with modest grade 2 GU and very low GI toxicity in selected low-risk and favorable IR patients. Unfavorable IR outcomes warrant further investigation of dose-escalation strategies. Risk group and postimplant V150% correlate with bPFS and postimplant GU-QOL score, respectively.

Proceedings of the 98^th Annual Meeting of the American Radium Society - americanradiumsociety.org