Prediction of PSA spikes by isotope and patient age following permanent prostate brachytherapy
15535 Background: To evaluate prostate specific antigen (PSA) spikes (bounces) following permanent prostate brachytherapy in low-risk patients randomized to Pd-103 or I-125. Methods: The study population consisted of 164 prostate cancer patients who were part of a prospective randomized trial comparing Pd-103 with I-125 for low-risk disease. Sixty-one patients (37.2%) received short course cytoreductive androgen deprivation therapy (ADT). No patient received supplemental XRT. The median follow-up was 5.4 years. All patients were implanted at least 3 years prior to analysis. On average, 10.1 post-treatment PSA’s were obtained per patient. Biochemical disease-free survival was defined as a PSA = 0.40 ng/mL after nadir. A PSA spike was defined as a rise of = 0.2 ng/mL followed by a durable decline to pre- spike levels. Multiple clinical, treatment and dosimetric parameters were evaluated as predictors for a PSA spike. Results: Forty- four patients (26.9%) developed a PSA spike including 45.7% (21/46) of the hormone naïve I-125 patients and 14.0% (8/57) of the hormone naïve Pd-103 patients. In hormone naïve patients, the mean time between implant and spike was 22.6 months and 18.7 months for I-125 and Pd-103 patients, respectively. In patients receiving neoadjuvant ADT, the incidence of spikes was comparable between isotopes (28.1% for I- 125 and 20.7% for Pd-103). The incidence of spikes was substantially different in patients < 65 vs = 65 years of age (16.3% vs. 38.5%). In multivariate Cox regression analysis, patient age at implant (p < 0.001) and isotope (p = 0.002) were significant predictors for spike. Conclusions: In low-risk prostate cancer patients, PSA spikes are most common in patients implanted with I-125 and/or younger than 65 years of age. Differences in isotope-related spikes are most pronounced in hormone naïve patients. No significant financial relationships to disclose.