The utility of 18F-Fluoride PET/CT for the detection of skull base involvement in nasopharyngeal carcinoma

Abstract

OBJECTIVES: 18F-FDG PET/CT (FDG) has a limitation in assessing skull base involvement in patients with nasopharyngeal carcinoma (NPC) but this assessment is essential for radiotherapy planning. We aimed at investigating the utility of 18F-Fluoride (F18) as an adjunct to FDG in the detection of skull base involvement in these patients. METHODS: All patients referred to PET scan for staging of histologically proven NPC from 2006 to 2009 were reviewed and those with FDG, F18 PET/CT and MRI within 1 month were recruited into this study. MRI was chosen as the preliminary standard of reference in place of invasive histopathological proof. FDG and F18 PET/CT scans were reviewed by 3 nuclear medicine physicians in consensus for the presence/absence of skull base involvement, and the level of confidence (1-3) was scored for each scan. MRI scans were reviewed by 2 radiologists. Reviewers were blinded to the other imaging modality. RESULTS: A total of 20 patients (M: 15, F: 5, mean: 48y) with 16 newly diagnosed and 4 recurrent NPC were evaluated. MRI detected 15 with and 5 without skull base involvement. FDG PET/CT detected 10 and F18 PET/CT detected 11 with skull base involvement, which were all true positive. Therefore the sensitivity, specificity and accuracy of FDG alone and F18 were 67% (10/15) vs 73% (11/15); 100% (5/5) vs 100% (5/5); and 75% (15/20) vs 80% (16/20) respectively. F18 increased the level of confidence for 12 and remained the same for 3. FDG was limited by ‘blooming’ effect or down scatter by intense uptake of the tumor or brain cortex, and faint equivocal uptake in the involved marrow. Non-specific uptake under benign conditions or irradiation changes for recurrent cases might lead to false interpretation of F18. CONCLUSIONS: F18 has an adjunctive role to FDG PET/CT in increasing the detection sensitivity and confidence of skull base involvement in NPC patients