Spectrum of metastatic and nonmetastatic skeletal findings with dual-phase 18F-FECH PET/CT in patients with biochemical relapse of prostate cancer.

INTRODUCTION: The aim of this study was to evaluate the spectrum of skeletal findings on dual-phase fluorine-18-fluoroethylcholine (F-FECH) PET/CT performed during the work-up of patients referred for suspected prostate cancer relapse.

MATERIALS AND METHODS: Three hundred F-FECH PET/CT scans were evaluated prospectively. The low-dose CT features of all cases were categorized as isodense, sclerotic, lytic or mixed lytic/sclerotic and maximum standardized uptake value (SUVmax) values were calculated. Findings on F-FECH PET/CT were correlated with Technetium-99m-methylene diphosphonate planar bone scans and serum prostate-specific antigen.

RESULTS: Patient age range was 50-90 years (median 71 years) and prostate-specific antigen values were in the range 0.04-372 ng/ml (Roche Modular method). Seventy-two lesions were detected on F-FECH PET/CT in 45 patients, including 31 (43%) in the pelvis, 17 (23%) in the spine (cervical 3, thoracic 8 and lumbar spine 6) and 10 (13%) in the ribs. Evaluation of low-dose CT in combination with PET helped to characterize benign findings in 21 (29%) lesions. The SUVmax for all except one benign lesion ranged from 0.49 to 2.15. In 51 (71%) lesions because of metastatic disease, SUVmax was 0.6-11.6 for those classified as sclerotic on low-dose CT, 0.7-8.58 for lytic lesions, 1.1-7.65 for isodense lesions and 1.27-3.53 for mixed lytic/sclerotic lesions. Of the 56 F-FECH-avid lesions, 21 lesions showed avidity on bone scan [3 (23%) of the 13 isodense lesions, 14 (40%) of the 35 sclerotic lesions, 2 (50%) of the lytic lesions and 2 (50%) of the mixed sclerotic/lytic lesions].

CONCLUSION: F-FECH PET/CT identified bone lesions in 15% of patients with suspected prostate cancer relapse. SUVmax in isolation cannot be used to characterize these lesions as benign or malignant. Minimal overlap of benign and malignant lesions was observed above SUVmax of 2.5. Low-dose CT of PET/CT is a useful tool to aid characterization.