18F-choline PET/CT in prostate cancer biochemical relapse after external beam radiotherapy or brachytherapy: Impact of PSA and kinetics

Aim. - To determine the impact of PSA and its kinetics on F-18-Choline PET/CT (FCH PET) ability to detect site of relapse in prostate cancer initially treated with external beam radiotherapy (EBRT) or brachytherapy (IBT). Methods. - We retrospectively enrolled PET FCH performed for suspicion of biochemical relapse after EBRT/IBT from January 2010 to January 2017 at Institut Curie. PSA(trigger), DPSA(nadir) (PSA(trigger)-PSA(nadir)), PSA doubling time (PSA(dt)) and velocity (PSA(vel)) were compared between positive and negative results. Logistic regression analysis was used to determine the relationship between these parameters and PET ability to detect True Positives (TP). Results. - In all, 271 FCH PET met the inclusion criteria: 169 after treatment with EBRT and 102 after IBT. Positivity rate was 67.9%, and 63.4% of TP were local relapses. Overall sensitivity and specificity were 81.2% and 71.0%. PSA(trigger) was 3.32 ng/mL (interquartile space: IQS 2.28-5.77) when PET was negative and 5.15 ng/mL (IQS 3.16-10.17) when positive, Delta PSA(nadir) was respectively 2.76 ng/mL (IQS 1.84-4.69) and 4.57 ng/mL (IQS 2.48-8.85), PSAdt 10.78 months (IQS 5.46-20.07) and 7.23 months (EI 2.58-14.14), and PSAvel 2.16 ng/mL/year (EI 1.02-4.80) et 4.92 ng/mL/year (1.89-16.02) (P < 0.001). Positivity rate increased with PSA(trigger) and Delta PSA(nadir). We found PSA(dt) <= 9 months (P = 0.029; OR = 2.97, IC95% [1.12-7.88]) and DPSA(nadir) >= 3 ng/mL (P = 0.03; OR = 2.56, IC95% [1.37-4.77]) to be independent predictive factors of PET sensitivity. Conclusion. - Detection of relapse after EBRT or IBT with PET FCH is influenced by PSA and its kinetics. In our study, PSA(dt) and Delta PSA(nadir) were independant predictors of PET performance, but initial treatment and tumor characteristics were not. (C) 2020 Elsevier Masson SAS. All rights reserved.