Cesium 131 versus iodine 125 implants for prostate cancer: evaluation of early PSA response.

INTRODUCTION: Given the shorter half-life of cesium-131 (Cs-131) compared to iodine-125 (I-125), we hypothesized that initial PSA outcomes may differ. We compare initial PSA outcomes in men undergoing Cs-131 prostate brachytherapy to men treated with I-125. PATIENTS AND METHODS: The first post-treatment PSA (obtained 3-6 months after the procedure) was compared in patients undergoing I-125 prostate brachytherapy to that of patients undergoing Cs-131 prostate brachytherapy at the same institution. Comparisons included the total cohort as well as low and intermediate risk patients. RESULTS: Mean pre-treatment PSA was 6.9 ng/mL in the I-125 cohort, and 6.9 ng/mL in the Cs-131 cohort. Mean initial post-treatment PSA was 0.9 ng/mL (range < 0.1-4.6) in the I-125 cohort and 1.2 ng/mL (range < 0.1-23.5) in the Cs-131 patients. For low risk patients, mean pre-treatment PSA was 5.8 ng/mL in the I-125 cohort, and 5.1 ng/mL in the Cs-131 cohort. Initial mean post-treatment PSA for low risk patients was 1.2 ng/mL (range < 0.1-4.6) in the I-125 group and 1.0 ng/mL (range < 0.1-2.9) in the Cs-131 patients (p = 0.37). For intermediate risk patients, mean pre-treatment PSA was 7.3 ng/mL in the I-125 cohort, and 7.3 ng/mL in the Cs-131 cohort. Mean initial post-treatment PSA in intermediate risk patients was 1.5 ng/mL (range < 0.1-2.9) in the I-125 group and 1.2 ng/mL (range < 0.1-4.6) in the Cs-131 patients (p = 0.52). CONCLUSIONS: Given the shorter half-life of Cs-131 compared to I-125, we hypothesized that initial post-brachytherapy PSA levels were similar between men receiving treatment with Cs-131 and I-125. The aim of the present study is not to predict long term outcome after Cs-131 prostate brachytherapy, but rather to simply compare initial PSA outcomes in men undergoing prostate brachytherapy with I-125 to Cs-131. Long term data are needed to document cancer control achieved with Cs-131.