Purpose: This study aimed to perform a prospective evaluation of 18F-NaF and 18F-FDG PET/CT in the detection of occult metastatic disease in men with prostate cancer and biochemical relapse.
Methods: Thirty-seven men with prostate-specific antigen (PSA) relapse (median, 3.2 ng/mL; range, 0.5-40.2 ng/mL) after definitive therapy for localized prostate cancer [26 radical prostatectomy (RP), 11 external beam radiation therapy] and negative conventional imaging underwent 18F-FDG and 18F-NaF PET/CT on 2 separate days within the same week. Studies were interpreted by 2 experienced radiologists in consensus for abnormal uptake suspicious for metastatic disease. The reference standard was a combination of imaging and clinical follow-up. Rank of PSA values for positive and negative PET/CT was compared using analysis of variance adjusting for primary therapy. Association between PSA and scan positivity in patients with RP was evaluated using Wilcoxon rank sum test.
Results: Result of the 18F-FDG PET/CT scan was positive for nodal disease in 2 patients. True-positive detection rate for occult osseous metastases by 18F-NaF PET/CT was 16.2%. Median PSA levels for positive versus negative PET/CT scans were 4.4 and 2.9 ng/mL, respectively, with the difference marginally significant in prostatectomized men (P=0.072). Percentages of patients with either 18F-NaF- or 18F-FDG-positive PET/CT in RP and external beam radiation therapy were 10% (n=10) and undefined (n=0) for a PSA of 2 ng/mL or less, 29% (n=7) and 50% (n=2) for PSA greater than 2 ng/mL but 4 ng/mL or less, 60% (n=5) and 40% (n=5) for PSA greater than 4 ng/mL but 10 ng/mL or less, and 25% (n=4) and 25% (n=4) for PSA greater than 10 ng/mL, respectively.
Conclusions: In biochemical relapse of prostate cancer, 18 F-NaF PET/CT is useful in the detection of occult osseous metastases, whereas the yield of 18F-FDG PET/CT is relatively limited. 18F-NaF PET/CT positivity tends to associate with increasing PSA level in prostatectomized men and may occur in lower PSA ranges than conventionally recognized.