Initial Clinical Outcomes of a Phase II Trial of Focal Salvage LDR Brachytherapy for Local Recurrence of Prostate Cancer after External Beam Radiation Therapy.

Abstract

To evaluate the clinical outcomes of focal salvage low dose rate brachytherapy (FSB) for biopsy proven local recurrence of prostate cancer after definitive external beam radiation therapy (EBRT). Patients with a Phoenix definition PSA recurrence (nadir + 2.0ng/dL) after definitive EBRT for localized prostate cancer and a negative metastatic work up were enrolled in a Phase II clinical trial. Patients first underwent MR-guided transperineal mapping biopsy of the prostate using a template grid. Patients with a pathologically confirmed recurrence underwent FSB using iodine-125 seeds to a prescription dose of 145 Gy. The brachytherapy planning target volume (PTV) was defined by the positions of the pathologically negative core biopsies adjacent to the positive core biopsies as recorded on the template grid during the biopsy procedure. An intraoperative treatment plan was then developed to cover the PTV with the 145 Gy isodose line. Follow up included assessment of genitourinary (GU) and gastrointestinal (GI) toxicities using Common Terminology Criteria for Adverse Events version 4.03 (CTCAEv4.03), patient reported outcomes using the International Prostate Symptom Score (IPSS) and Expanded Prostate Cancer Index-26 (EPIC-26) forms, and serial PSA blood draws. Ten patients underwent FSB. The median prior EBRT dose was 7805 cGy (interquartile range IQR 7560-7920) and the median time from completion of EBRT to FSB was 81 months (IQR 68-134). The median PSA prior to FSB was 3.2 ng/dL (IQR 2.3 - 4.5). The median follow up after FSB was 32 months (IQR 18-57). Eight patients were free of Phoenix definition PSA failure at last follow up. Of the two patients who experienced a PSA failure, one developed distant metastases 5 months after FSB and the other a biopsy proven seminal vesicle recurrence 3 years after FSB. The median change in post FSB IPSS score compared to the pre-FSB IPSS score was an increase of 1.5 (IQR -1.5 to 8) at 3 month follow up and an increase of 3.5 (IQR 0.5 to 5.5) at last follow up (≥1 year). The median change in post FSB EPIC-26 urinary domain score compared to the pre-FSB score was -1 (IQR -26 to +14.5) at 3 month follow up and +2 (IQR -12.5 to +14.5) at last follow up (≥1 year). The median change in post FSB EPIC-26 bowel domain score compared to the pre-FSB score was -2 (IQR -9.5 to 0.0) at 3 month follow up and 0 (IQR -6.0 to +3.0) at last follow up (≥1 year). No patients experienced post FSB Grade 3 or higher GU or GI toxicities. High dose FSB for a local recurrence of prostate cancer after EBRT can be delivered with good biochemical control and a favorable toxicity profile. Further clinical trial enrollment and longer follow up will be needed to better assess long term outcomes.