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Oncology-Clinical Diagnosis: Solid TumorsHead and Neck Cancer |
1 Hokkaido University, Sapporo, Japan
455
Objectives: 11C-methionine PET(MET-PET) has been used to distinguish brain tumor recurrence from radiation necrosis. However it has not been investigated whether MET-PET has similar diagnostic value in small size lesions. The aim of this study is to investigate diagnostic value for evaluating small lesions in comparison with large lesions.
Methods: This study included 31 patients(34 lesions) who were suspected recurrent brain tumors after radiation therapy. These lesions were divided into two groups; large group with 
15mm in diameter (15-52mm, n=20) and small group with <15mm in diameter (4-14mm, n=14). PET images were obtained as a static scan of 3 or 10 minutes performed 20 minutes after injection of 11C-methionine (355.1±126.5MBq). All images were interpreted visually by at least two experienced nuclear physicians by consensus. Semi-quantitative analysis was performed using tumor-versus-normal ratio(T/N ratio).
Results: Histological analysis or clinical course confirmed 23 with tumor recurrence and 11 with radiation necrosis. In the large groups, sensitivity and specificity were 100%(16/16) and 50%(2/4). In the small group, sensitivity and specificity were 100%(7/7) and 100%(7/7). MET-PET demonstrated very high sensitivity not only in the large group but also in the small group. T/N ratio in recurrence and necrosis were 2.01±0.57 and 1.05±0.10(P<0.01) in the large group, and 1.82±0.26 and 1.00±0.35(P<0.01) in the small group. Significant difference was observed between recurrence and necrosis in both groups.
Conclusions: 11C-methionine PET is very useful to distinguish brain tumor recurrence from radiation necrosis both by visual and semi-quantitative analysis even in small size lesions.
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