Abstract
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Objectives: To evaluate the factors influencing the positivity rate of commercial 18F-fluciclovine positron emission tomography/computed tomography (PET/CT) in clinical practice.
Methods: We performed a retrospective cohort study of 152 men with suspected biochemical recurrence of prostate cancer after initial treatment who underwent 18F-fluciclovine PET/CT scans between December 2016 and September 2017 at our institution. Positivity rates (PR) were calculated for whole body, prostate/bed, and extraprostate locations. The influence of different factors such as absolute PSA level, PSA kinetics, Gleason group (GG) and initial treatment type on PR was evaluated.
Results: Mean patients' age was 68.7 years (IQR 64 - 73). 147 patients had pre-PET PSA available with median level of 2.06 ng/ml (IQR 0.5 - 5.2). For 67 patients, PSA doubling time (DT) could be calculated with a median of 6.32 months (IQR 3.38 - 9.67). PR was 81% (123/152) for whole-body, 61% (92/152) for prostate/bed, and 55% (83/152) for extraprostate locations. Among patients with known PSA levels, PR was 81% (119/147) for whole body, 61% (89/147) for prostate/bed, and 54% (80/147) for extraprostate locations. There was a linear increase trend in PR with increasing PSA level (p < .001). For whole body, the PR for PSA levels of < 1, 1-<2, 2-<5, and ≥5 were 58% (32/55), 87% (13/15), 100% (39/39), and 92% (35/38), respectively. For prostate/bed, PR for PSA levels of < 1, 1-<2, 2-<5, and ≥5 were 35% (19/55), 60% (9/15), 74% (29/39) and 84% (32/38), respectively. For extraprostate locations, PR for PSA levels of < 1, 1-<2, 2-<5, and ≥5 were 38% (21/55), 60% (9/15), 64% (25/39), and 66% (25/38), respectively. For PSA <0.5 (n=28), whole body PR was 57% (16/28). No statistically significant linear trend was found between PR and PSA DT or velocity (p>0.05). Additionally, no statistically significant linear trend was found between PR and increasing GG. The whole-body PR for GG of ≤ 2 was 82% (37/45) and 78% (39/50) for GG ≥ 3 (p>0.05). However, for every one-unit increase in patients’ Gleason score, the odds of a positive finding in the extraprostate location increased by 49% (OR = 1.49, 95% CI: 1.03 - 2.20; p = .03). Compared to patients who only underwent prostatectomy, patients who underwent brachytherapy (BT) + hormonal therapy (HT) were more likely to have a positive finding in the prostate/bed (OR = 37.04; p = .02), as were those receiving only external beam radiotherapy (EBRT) (OR = 26.07; p = .04) and those receiving only BT (OR = 19.67; p = .001). CONCLUSION: 18F-fluciclovine PET/CT PR is dependent upon PSA levels, GG, and initial treatment. Positive scans are overall associated with higher PSA levels. History of radiotherapy (BT or EBRT) is associated with higher positive findings in the prostate. Patients with higher GG are more likely to have extraprostatic uptake.