Isotope selection and PSA failure in prostate seed implant: Experience with CS-131 in a community hospital system.

Abstract

375 Background: A recent large single institutional study reported excellent long-term biochemical control and survival for Cs-131 prostate implant. This isotope has short half-life (9.7 days) with clinical advantages including shorter duration of symptoms. We previously showed Cs-131 dosimetry to be quantitatively similar to I-125 with improved homogeneity (mean percent V150 36% for I-125 versus 27% for Cs-131 (p < 0.0001). Our objective was to evaluate PSA failure rates and dosimetric outcomes in a multi-institutional community based setting. Methods: Within an IRB approved retrospective study, we compared outcomes for three groups of permanent prostate implant patients treated at Ascension Macomb Oakland, Ascension Saint John, and Ascension Providence Rochester Hospitals over a 10 year time interval. The comparison groups included isotopes Cs-131 (n = 66; t1/2 9.7 days), I-125 (n = 60; t1/2 60 days), and Pd-103 (n = 60; t1/2 17 days). Kaplan Meier estimates of PSA failure used the nadir plus 2 (Phoenix) definition. Results: Standard permanent implant doses employed were 145 Gy for I-125 monotherapy or 109 Gy for combination therapy. The dose for Cs-131 was 115 Gy for monotherapy and 85 Gy for combination therapy. For Pd-103, the doses employed were 125 Gy and 90 Gy for mono- and combination therapy, respectively. Median age at diagnosis was Cs-131; 69 (range 49-80), I-125; 71 (49-78), and Pd-103; 70 (60-82). Mean pretreatment PSA values were Cs-131 5.73 ng/ml, I-125 6.62 ng/ml, and for Pd-103 8.87 ng/ml. Median PSA follow up was 30 months and the median PSA value at 60 months was 0.11 ng/ml. There was excellent PSA control for all three groups of cases (p = NS), however with fewer failures using Cs-131. Conclusions: Permanent interstitial brachytherapy continues to be an attractive option for treatment early stage prostate cancer. Only a few large single institutional studies have examined PSA failure rates or dosimetric aspects of shorter half-life Cs-131 seed implants. This series confirms wide applicability of Cs-131 permanent prostate seed implant in the community hospital setting.