Comparison of whole-body versus limited whole-body 18F-FDG PET/CT scan in malignant cutaneous melanoma

OBJECTIVES: The objectives of this study were to estimate retrospectively the incidence of clinically significant findings in the lower extremities in patients with malignant cutaneous melanoma scanned from the skull vertex to the bottom of the feet and whether these add additional diagnostic and prognostic information and to demonstrate a confidence interval that would support exclusion of lower-extremity scans in these patients. METHODS: This is a retrospective study of 200 patients who underwent F-FDG PET/CT for staging melanoma. Whole-body PET/CT scans including the lower extremities were reviewed. PET/CT findings in the lower extremities were tabulated by location, pathology, and clinical progress notes with documented clinical history and physical examination correlation. RESULTS: Among the 200 PET/CT scans, 3 scans had positive findings in the lower extremities. A biopsy was performed on 1 lesion, which was found to be an incidental squamous cell carcinoma. One lesion was considered a benign finding from inflammation demonstrated by clinical follow-up. One scan had a metastasis to the proximal femur, which is included in the standard FOV (eyes to midthighs). In this case series, the lower extremities' true-positive findings never impacted or changed clinical management. CONCLUSIONS: Our study confirms with a high degree of confidence that in patients with malignant cutaneous melanoma, additional lower-extremity scan results in little additional useful information and could be discontinued in patients whose melanoma did not arise in the lower extremities. PET/CT acquisition of the lower extremities results in increased scan time and unnecessary extra radiation dose from CT to melanoma patients.