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High-Risk Melanoma: Accuracy of FDG PET/CT with Added CT Morphologic Information for Detection of Metastases¹

¹ From the Division of Nuclear Medicine, Department of Medical Radiology (K.S., D.B.H., M.P.L., T.F.H., H.C.S.), and Department of Dermatology (R.D.), University Hospital Zurich, Raemistr 100, 8091 Zurich, Switzerland. Received June 26, 2006; revision requested August 30; revision received September 15; accepted October 25; final version accepted December 11. Supported in part by the Bonizzi-Theler Foundation. Address correspondence to K.S. (e-mail: klaus.strobel{at}usz.ch).

Purpose: To prospectively determine the accuracy of positron emission tomography (PET)/computed tomography (CT) with added CT morphologic information for depiction of metastases in patients with high-risk melanoma and negative findings for metastases at PET, by using histologic findings or additional imaging and/or follow-up findings as reference standard.

Materials and Methods: Institutional review board approval was obtained. Informed consent was obtained from patients. One hundred twenty-four consecutive high-risk melanoma patients (65 female, 59 male; mean age, 54.4 years; range, 15–82 years) were included. Fluorine 18 fluorodeoxyglucose (FDG) PET/CT was performed. First, PET/CT scans were evaluated for presence of metastases with increased FDG uptake; CT anatomic location was determined. Lesions were considered metastases if there was focal uptake higher than that of background tissue. Second, coregistered CT images of combined PET/CT scans were evaluated for presence of lesions without FDG uptake. Findings were compared with reference standard findings to determine the accuracy of each evaluation. McNemar test was used to assess statistical differences in accuracy.

Results: In 53 of 124 patients, metastases were found. In 46 of 53 patients with metastases, lesions had increased FDG uptake. In seven patients with metastatic disease, metastases did not have increased FDG uptake (maximum standard uptake value [SUV], <1.5; n = 5) or had faint FDG uptake (maximum SUV, 2.5 and 2.9; n = 2)—findings that were inconclusive with PET alone. These lesions were interpreted as metastases only with coregistered CT images. Lesions missed with PET were located in the lungs, iliac lymph nodes, subcutis, and psoas muscle. Sensitivity, specificity, and accuracy, respectively, of PET/CT for depiction of metastases were 85%, 96%, and 91%, and those of PET/CT with dedicated CT interpretation were 98%, 94%, and 96% (P = .016).

Conclusion: Dedicated analysis of coregistered CT images significantly improves the accuracy of integrated PET/CT for depiction of metastases in patients with high-risk melanoma.

© RSNA, 2007

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