Evaluation of [68Ga]Ga-PSMA PET/CT for therapy response assessment of [177Lu]Lu-PSMA radioligand therapy in metastasized castration refractory prostate cancer and correlation with survival

Purpose The aim of this retrospective study was to evaluate the use of [Ga-68]Ga-PSMA PET/CT in therapy response assessment (TRA) of mCRPC patients treated with [Lu-177]Lu-PSMA-617 and its correlation with overall survival (OS). Methods Thirty-nine patients were included in the study. Patient-/lesion-based early and late response assessment (ERA/LRA) was defined as PET2 (after two therapy cycles) vs. PET1 (before the first cycle) (n = 29) and end of treatment PET vs. PET1 (n = 17), respectively. PET-based response (PET parameters; modified (m) PERCIST/EORTC), biochemical response (Delta PSA; category-based) and category-based clinical response (CRA) was tested for correlation/agreement. PET-based TRA was correlated with OS. Results A significant correlation/agreement was shown between PET parameters and CRA as well as biochemical response in LRA of all lesions and between mPERCIST-based and category-based PSA response assessment in LRA (bone lesion-based, P = 0.045, kappa = 0.184). At ERA, OS was significantly higher in CR/PR/SD compared to progressive disease applying mPERCIST/EORTC criteria (P = 0.0024). Conclusion In [Lu-177]Lu-PSMA-617-treated mCRPC patients OS of the group of CR/PR/SD was significantly higher compared to the progressive disease group (mPERCIST/EORTC) in ERA. Therefore, [Ga-68]Ga-PSMA PET might serve as a complementary diagnostic tool for TRA offering prognostic value regarding OS.