Detection of failure patterns using advanced imaging in patients with biochemical recurrence following low-dose-rate brachytherapy for prostate cancer

Purpose/Objective(s) Low dose rate (LDR) brachytherapy alone or with external beam radiation (EBRT) results in excellent rates of biochemical control in patients (pts) with prostate cancer (PCa). Understanding failure patterns in pts with biochemical recurrence (BCR) may inform implant technique or pt selection. The primary objective of this study was to describe locations of recurrence on multiparametric MRI (mpMRI) and prostate specific membrane antigen (PSMA) imaging in pts with BCR after LDR brachytherapy. Materials/Methods Pts with BCR after definitive LDR (± EBRT, ± androgen deprivation therapy (ADT)) referred for IRB approved imaging protocols were included. All pts underwent 3T mpMRI (T2 weighted, dynamic contrast-enhanced, and diffusion-weighted imaging) prospectively reviewed by prostate-dedicated radiologists. A subset of pts underwent PSMA-PET/CT imaging. Pathologic confirmation was obtained unless contraindicated. Prostate lesions were categorized as left (L)/right (R)/midline (ML); transitional zone (TZ)/peripheral zone (PZ); apical/mid/base; and anterior/posterior/central. Locations of recurrence (prostate, seminal vesicles (SV), lymph nodes (LN) and distant metastases (DM)) were recorded and reported descriptively. Results Between Jan 2011 and Feb 2021, 57 pts with BCR after LDR underwent prostate mpMRI. Treatment was LDR (n = 39) or EBRT + LDR (n = 18), ± ADT (n = 12). At time of LDR, initial Gleason score was ≤ 6 (n = 29), 7 (n = 19), 8-9 (n = 8), unknown (n = 1) and median PSA was 6 ng/mL (3.4-49). Of dosimetry available (n = 27), 2 had D90 Conclusion In this cohort of pts with BCR following LDR, the predominant locations of local recurrence were in the anterior/central TZ and SV. PSMA corroborated the majority of mpMRI findings and often demonstrated LN and DM. These findings may inform LDR technique and impact patient selection or pre-treatment imaging evaluation; and should be confirmed in larger subsets and correlated with post-implant dosimetry.