Utility of FDG PET-CT in the evaluation of ocular melanoma

Abstract

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Objectives: Early detection of metastatic ocular melanoma is an important prognostic factor and often indicates poor prognosis. The aim of this study was to evaluate the role of F-18-FDG PET/CT in detection of primary ocular melanoma, distant metastasis, and response to therapy. Methods: The authors retrospectively analyzed 146 whole-body FDG PET/CT scans performed in 119 patients referred for initial staging (n=103 patients) and re-staging (n=34, 43 studies) of ocular melanoma. All patients fasted for at least 4 hours. Whole body PET/CT images were obtained with a PET/CT scanner (GE Discovery) approximately 75 minutes after administration of 10-15 mCi FDG. Results: PET/CT demonstrates FDG uptake corresponding to the primary lesion in the orbit (18.5%, 27/146 scans) in 25 patients. Among these 25 patients, 9 underwent 20 scans: 9 baseline scan and 11 follow-up scan 3 to 6 months after therapy (i.e. 8 brachytherapy, 1 enucleation). PET/CT demonstrate complete response in 7/9 (78%) of the patients, 1 partial and 1 mixed response. PET/CT identified only medium size (10-15mm) and large size ocular melanoma (>15 mm). The max SUV orbital uptake of large ocular melanoma (5.08±2.68) was statistically higher than medium ocular melanoma uptake (3.38±0.93, P<0.05). Of the 25 patients with FDG-avid orbital lesions, extraorbital neoplastic disease was seen in 5 of them. Thirteen of 146 (8.9%) scans performed showed no evidence of FDG activity in the orbits but demonstrated extraorbital neoplastic disease at the following sites: liver (n=3 patients), breast (n=1), lung (n=4), lymph nodes (n=3), thyroid (n=1) and bone (n=2). Overall, PET/CT detected extraorbital disease in 12.3% (18/146) of the studies. PET/CT detected a second primary in initial staging of 3 patients (2 lung and one breast cancer) all confirmed by histopathology. Conclusions: FDG uptake in the orbits is affected by the size of the ocular melanoma. FDG PET/CT was unable to identified small ocular melanoma (<10mm) likely due to low resolution of the system and biological characteristic of melanoma. Our data indicates that FDG PET/CT can prove valuable in detecting metastatic disease and assessing local response to radiation therapy to the eye in patients with ocular melanoma.