Assessment of the role of Ga-68 PSMA I&T PET/CT in response evaluation to docetaxel therapy in castration resistant prostate cancer patients

Objective: There have been only few studies investigating the role of PSMA ligands in the therapy response assessment of metastasized castration resistant prostate cancer (mCRPC) cases. In this study we aimed at evaluating the capability of Ga-68- prostate-specific membrane antigen (PSMA) I&T positron emission tomography/computerized tomography (PET/CT) in the assessment of therapeutic response in patients under docetaxel therapy for prostate cancer (PCa). Material and methods: The clinical records of all mCRPC patients treated with docetaxel and referred to our department for Ga-68-PSMA I&T PET/CT imaging were retrospectively analysed. Sixteen patients (mean age 69 years, range 52-82 years) with castration-resistant prostate cancer patients receiving palliative docetaxel therapy and had undergone Ga-68-PSMA I&T PET/CT scan were included in the study. Ga-68-PSMA I&T PET/CT imaging was done and prostate specific antigen (PSA) levels were measured at baseline before administration of docetaxel (PET1) and after at least 3 cycles (range 4-12) of chemotherapy (PET2). Patient-based as well as lesion-based comparison of PET2 findings with PET1 findings were done. Results: The change (decrease) observed in lymph node and prostate gland/prostatic bed SUVmax values after treatment compared to pretreatment was found to be statistically significant (P-.033). 3/16 patients (19%) were classified as progressive disease (PD), 4/16 (25%) as stable disease (SD), 9/16 (56%) as partial remission (PR) radiologically. An increasing PSA trend (IT) was observed in 4 patients (25%) and a decreasing PSA trend (DT) in 3 patients (18%). Nine patients showed a PSA response of >= 50% (56%). Of the 4 patients showing SD, 3 had IT, 3 had BR. Of the 9 patients who showed PR on PET studies, 8 patients showed BR and 1 patient showed DT. Conclusion: Imaging with Ga-68-PSMA PET/CT showed great concordance with biochemical response evaluation in terms of PSA levels, especially in patients showing good response to therapy. Ga-68-PSMA PET/CT was also successful in identifying progressive disease in patients showing paradoxical decline in PSA levels. (C) 2020 Sociedad Espanola de Medicina Nuclear e Imagen Molecular. Published by Elsevier Espana, S.L.U. All rights reserved.