Gallium-68-Labeled Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography Response in Pelvic Node-Positive Prostate Cancer After Definitive Radiation Therapy: Prognostic Implications.

Abstract

The purpose of this study was to evaluate the prognostic value of metabolic response assessed by Gallium-68-labeled prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA-PET/CT) in prostate cancer (PCa) patients with pelvic lymph node metastases (PLNM) undergoing definitive radiation therapy (RT) and androgen deprivation therapy (ADT). This retrospective study analyzed 107 patients with PCa and PLNM treated between October 2015 and June 2023. All patients underwent pre- and post-treatment ⁶⁸Ga-PSMA-PET/CT scans for staging, RT planning, and response assessment. Each patient received prostate and pelvic field RT, underwent ADT for at least 18 months, and had a minimum follow-up period of 24 months. The primary endpoint was distant metastasis-free survival (DMFS), whereas progression-free survival (PFS) and prostate cancer-specific survival (PCSS) were evaluated as secondary endpoints. Over a median follow-up of 60.4 months, post-treatment ⁶⁸Ga-PSMA-PET/CT obtained at a median of 4.1 months after RT showed SUVmax reductions in 98.1% of primary tumors and 93.5% of lymph nodes, with complete metabolic response (CMR) in 43.9% of primary tumors and 65.4% of lymph nodes. Primary tumor CMR was associated with improved 5-year DMFS (81.6% vs 61.4%; P = .006), PFS (72.2% vs 41.0%; P = .01), and PCSS (96.4% vs 84.7%; P = .04). Lymph node CMR correlated with superior 5-year DMFS (87.3% vs 42.6%; P < .001), PFS (72.6% vs 25.9%; P < .001), and PCSS (97.5% vs 77.1%; P < .001). In multivariable analysis, longer ADT duration (≥24 months) and lymph node CMR were independent predictors of improved DMFS, PFS, and PCSS, whereas Gleason score ≥8 was associated with poorer DMFS. Metabolic response on post-treatment ⁶⁸Ga-PSMA-PET/CT is a significant predictor of long-term outcomes in patients with PCa and PLNM. Lymph node CMR and prolonged ADT (≥24 months) were independent predictors of improved survival, supporting the use of ⁶⁸Ga-PSMA-PET/CT for post-treatment response assessment in PCa with PLNM.