151 Background: Prostate cancer patients continue to seek out minimally invasive therapies with equal disease eradication, but with less morbidity, lower cost and multiple salvage options. Our objective was to evaluate PSA response and determine rate of prostate specific antigen (PSA) kinetics in patients undergoing permanent low dose rate (LDR) focal prostate brachytherapy at a single institution. Methods: Between 4/2015 – 1/2017, 52 patients, of which 25% of patients were diagnosed with prostate cancer using a stereotactic transperineal mapping biopsy approach, while 75% had a standard transrectal prostate biopsy, were treated with LDR focal prostate brachytherapy. Dose to target was 115 Gy using Cesium-131. 30 patients (57.7%) were considered low risk, 21 pts (40.4%) were intermediate, and 1 patient (1.9%) was high risk. Treatment was limited to the side of the gland where the cancer was diagnosed. Because there is no agreed upon standard regarding PSA control, we are choosing to call the percent change in PSA the “Impact PSA”. Results: Median pre-treatment prostate volume was 51.6 cm3 (range 18 – 129 cm3), while the median target volume was 17.8 cm3 (range 7.6 – 39.4 cm3). Additionally, the median prostate volume treated was 33.73% (range 17.6 – 95.3%). Our data demonstrates that patients in whom 25-50% of the gland treated, resulted in an Impact PSA of approximately 25% - 50% decrease in total PSA between 3 - 6 months, with continued decreases of 55% at 1 year, and 77% at 2 years. Conclusions: Focal therapy outcomes are highly variable and related to volume of ablation. For low volume disease, LDR focal brachytherapy may be a viable option for patients. Optimal outcome assessment after focal therapy is yet to be determined. Since there is untreated gland with the potential to produce PSA, perhaps stable patterns in PSA kinetics, rather than a nadir, is more valuable. We will continue to follow-up with this cohort to report long term results and closely study the Impact PSA.
EP-1337: PSA Kinetics: HDR prostate brachytherapy boost in combination with external beam radiotherapy
