PP06 Presentation Time: 9:50 AM: Biochemical Failure-Free Survival Rates After Brachytherapy with I-125, Pd-103, or Cs-131 for Intermediate-Risk Prostate Cancer: Phase II Trial

Abstract

<h3>Background</h3> Iodine (I)-125 is traditionally used for low-dose-rate (LDR) brachytherapy for prostate cancer, but emerging data support the use of cesium (Cs)-131 or palladium (Pd)-103 as well. Although the safety and effectiveness of these three isotopes for intermediate risk prostate cancer have been established, the relative efficacy of each is unknown. <h3>Purpose</h3> To compare biochemical outcomes after I-125, Pd-103, or Cs-131 brachytherapy as definitive treatment for intermediate-risk prostate cancer. <h3>Materials and Methods</h3> This prospective phase II trial evaluated ultrasound-guided LDR brachytherapy monotherapy as definitive treatment for intermediate-risk prostate cancer at a single institution in 2006-2013. The choice of isotope and corresponding prescribed dose was made sequentially (starting with I-125, D=144 Gy; followed by Pd-103, D=125 Gy; then Cs-131, D=115 Gy. Patients had intermediate-risk disease (Gleason score [GS] 6 or 7 [3+4 or 4+3]), no evidence of nodal or metastatic disease, and no prior hormonal or radiation therapy. Follow-up visits were every 4 months for the first year after the implant, every 6 months for the next 5 years, and yearly thereafter, with prostate-specific antigen (PSA) levels measured at each visit. Biochemical failure (BCF) was defined per the Phoenix criteria as an increase in PSA value to nadir +2 ng/dL or radiologic or histologic evidence of recurrence with increasing PSA value. Patients were considered to have no evidence of disease (NED) if the PSA was <0.2 ng/dL at the specified time. Treatment efficacy was defined as time to BCF and the presence or absence of NED at a given time. Kaplan-Meier analysis was used to estimate BCF-free survival rates by isotope, with between-group differences assessed with log-rank tests. One-way analysis of variance was used to compare time to BCF between groups. Simple linear regression was used to determine the influence of isotope on achieving NED. <h3>Results</h3> Of the 300 patients in this trial (median age 64.9 years), 100 were treated with Cs-131, 98 with I-125, and 102 with Pd-103. Eleven patients (3.7%) had GS 6 disease, 236 (78.7%) had GS 7 (3+4) disease, and 53 (17.7%) had GS 7 (4+3) disease; 195 (65.0%) had favorable intermediate-risk, and 105 (35.0%) had unfavorable intermediate-risk disease. The median follow-up time was 8.7 years. During follow-up, 27 patients (9.0%) experienced BCF, 7 (7%) in the Cs-131 group, 13 (13.3%) in the I-125 group, and 7 (7.1%) in the Pd-103 group. Among those 27 patients with BCF, 10 (37.0%) received salvage therapy with surgery, brachytherapy, radiation therapy, or cryotherapy. The BCF-free survival rates were 93% for those treated with Cs-131, 86.7% for I-125, and 93.1% for Pd-103 (p=0.86) (Figure); the median time was not reached because of the short follow-up and the limited number of events. Follow-up data were available for 101 patients at 8.7 years; 100 patients (99%) had NED. Although 36 patients (12%) died during the study, only 1 death (0.3%) was related to prostate cancer. <h3>Conclusions</h3> No significant differences in efficacy were found among Cs-131, Pd-103, and I-125 for LDR brachytherapy monotherapy for intermediate-risk prostate cancer. The choice of isotope should be based on dosimetric advantages, estimated risk of toxicity, and quality-of-life profile. A larger randomized trial is needed to assess potential differences in efficacy among isotopes.