18 F-Fluciclovine parameters on targeted prostate biopsy associated with true positivity in recurrent prostate cancer.

We evaluated 18 F-fluciclovine uptake parameters that correlate with true positivity for local recurrence in non-prostatectomy treated patients. Methods: Twenty-one patients (prostate-specific antigen 7.4±6.8 ng/ml) with biochemical recurrence after non-prostatectomy local therapy (radiotherapy and cryotherapy) had dual time-point 18 F-fluciclovine (364.1±37.7 MBq) positron emission tomography (PET)/computed tomography from pelvis to diaphragm. Prostatic uptake over background was delineated and co-registered to a prostate biopsy planning ultrasound. Trans-rectal biopsies of 18 F-fluciclovine defined targets were completed using a 3-D visualization and navigation platform. Histologic analyses of lesions were completed. Lesion characteristics including maximum standardized uptake value (SUVmax ), target-to-background ratio (TBR), uptake pattern, and subjective reader's suspicion level were compared between true positive (malignant) and false positive (benign) lesions. Univariate analysis was used to determine the association between PET and histologic findings. Receiver Operating Characteristic (ROC) curves were plotted to determine discriminatory cut-off points of TBR. Statistical significance was set at p<0.05. Results: Fifty lesions were identified in 21 patients on PET. 17/50 (34.0%) targeted lesions in 10/21 patients were positive for malignancy. True positive lesions had significantly higher SUVmax (6.62±1.70 vs 4.92±1.27), TBR (marrow) (2.57±0.81 vs 1.69±0.51), and TBR (blood pool) (4.10±1.17 vs 2.99±1.01) than false positive lesions at the early time-point (p<0.01), and remained significant at the delayed time-point except TBR (blood pool). Focal uptake (Odds Ratio (OR): 12.07 [95% Confidence Interval (CI): 2.98-48.80], p<0.01) and subjective highest suspicion level (OR: 10.91 [95% CI: 1.19-99.69], P = 0.03) correlated with true positivity. Using the ROC, optimal cut-offs for TBR (marrow) were 1.9 (Area under the curve [AUC]=0.82) and 1.8 (AUC=0.85) at early and delayed imaging, respectively. With these cut-offs, 15/17 malignant lesions were identified at both time-points, however, fewer false positive lesions were detected at delayed (5/33) compared to early (11/33) time-point. Conclusion: True positivity of 18 F-fluciclovine targeted prostate biopsy in non-prostatectomy treated patients correlates with focal uptake, TBR (blood pool and marrow), and subjective highest suspicion level. TBR (marrow) of 1.9 at early time-point and 1.8 at delayed time-point had optimal discriminating capabilities. Despite the relatively low intra-prostate positive predictive value (34.0%) with 18 F-fluciclovine, application of these parameters to interpretative criteria may improve true positivity in the treated prostate.