Dixon-based MR imaging for MR AC allows for anatomical allocation of PET-positive lesions similar to low-dose CT in conventional PET/CT. Thus, this approach appears to be useful for future MR/PET for body regions not fully covered by diagnostic MRI due to potential time constraints.

The purpose of this study was to investigate the effect of total prostate-specific antigen (PSA) at the time of 11 C-choline PET/ CT (trigger PSA), PSA velocity (PSAvel), and PSA doubling time (PSAdt) on 11 C-choline PET/CT detection rate in patients treated with radical prostatectomy for prostate cancer, who showed biochemical failure during follow-up. Methods: A total of 190 patients treated with radical prostatectomy for prostate cancer who showed an increase in PSA (mean, 4.2; median, 2.1; range, 0.2-25.4 ng/mL) were retrospectively enrolled. All patients were studied with 11 C-choline PET/CT. Patients were grouped according to trigger PSA (PSA # 1 ng/mL, 1 , PSA # 2 ng/mL, 2 , PSA # 5 ng/mL, and PSA . 5 ng/mL). In 106 patients, data were available for calculation of PSAvel and PSAdt. Logistic regression analysis was used to determine whether there was a relationship between PSA levels and PSA kinetics and the rate of detection of relapse using PET. Results: 11 C-choline PET/CT detected disease relapse in 74 of 190 patients (38.9%). The detection rate of 11 C-choline PET/CT was 19%, 25%, 41%, and 67% in the 4 subgroups-PSA # 1 ng/mL (51 patients), 1 , PSA # 2 ng/mL (39 patients), 2 , PSA # 5 ng/mL (51 patients), and PSA . 5 ng/mL (49 patients)-respectively. Trigger PSA values were statistically different between PET-positive patients (median PSA, 4.0 ng/mL) and PET-negative patients (median PSA, 1.4 ng/mL) (P 5 0.0001). Receiver-operating-characteristic analysis showed an optimal cutoff point for trigger PSA of 2.43 ng/mL (area under the curve, 0.76). In 106 patients, PSAdt and PSAvel values were statistically different between patients with PET-positive and -negative scan findings (P 5 0.04 and P 5 0.03). The 11 C-choline PET/CT detection rate was 12%, 34%, 42%, and 70%, respectively, in patients with PSAvel , 1 ng/mL/y (33 patients), 1 , PSAvel # 2 ng/mL/y (26 patients), 2 , PSAvel # 5 ng/mL/y (19 patients), and PSAvel . 5 ng/mL/y (28 patients). The 11 C-choline PET/CT detection rate was 20%, 40%, 48%, and 60%, respectively, in patients with PSAdt . 6 mo (45 patients), 4 , PSAdt # 6 mo (20 patients), 2 , PSAdt # 4 mo (31 patients), and PSAdt # 2 mo (10 patients). There was no statistical difference between PET-positive and -negative scan detection rates according to the Gleason score, pT and N status, patient age, or duration between surgery and biochemical relapse. Trigger PSA and PSAvel were found to be independent predictive factors for a PET-positive result (P 5 0.002; P 5 0.04) and PSAdt was found to be an independent factor only in patients with trigger PSA less than 2 ng/mL (P 5 0.05) using multivariate analysis. Conclusion: The 11 C-choline PET/CT detection rate is influenced by trigger PSA, PSAdt, and PSAvel. This finding could be used to improve the selection of patients for scanning by reducing the number of false-negative scans and increasing the detection rate of disease in patients with early relapse and potentially curative disease.

In our study, (11)C-choline PET/CT was able to detect recurrent disease in 28% of the patients with mild biochemical relapse characterized by very low trigger PSA levels (PSA <1.5 ng/ml). Very interestingly (11)C-choline PET/CT detected distant unexpected metastases in 21% of the patients. At multivariate statistical analysis only PSAdt and node status were shown to be significant and independent predictive factors for positive (11)C-choline PET/CT. Therefore, (11)C-choline could be suggested to be performed early during initial biochemical relapse in patients presenting with fast PSA kinetics. The early detection of the site of recurrence could lead to a prompt instauration of the most appropriate treatment, i.e. local surgery or radiation treatment vs systemic treatment. In this view, one of the main advantages should be the avoidance of unnecessary local radiotherapy in those patients showing distant metastasis at (11)C-choline PET/CT.