Abstract
151
Objectives: Malignant peripheral nerve sheath tumors (MPNSTs) lead to a poor prognosis for neurofibromatosis type 1 patients. 18F-FDG PET image with a T/L (Tumor/Liver) SUVmax ratio was reported to improve the detection of malignancies compared with SUVmax cut-off of >3.5. However, the criteria for malignancy were not standardized. Therefore, the aim of the study was to evaluate the diagnostic accuracy of SUVmax on 18F-FDG PET/CT to different reference tissue uptake (tumor-to-liver, tumor-to-muscle and tumor-to-fat ratios) for determining MPNSTs . Methods Eighteen patients with NF1 who underwent whole-body PET/CT were defined as benign or malignant tumor by biopsy. PET/CT images were evaluated for the distribution and uptake pattern, and the intratumor tracer uptake (SUVmax) was normalised to three different reference tissues (tumor-to-liver T/L, tumor-to-muscle T/M and tumor-to-fat T/F ratios). Receiver operating characteristic (ROC) analyses were used out to assess the diagnostic accuracy among different reference tissue uptake . Results Twenty-nine lesions were identified of FDG PET/CT, 5 lesions were confirmed as malignant by biopsy. The comparison of SUVmax had no significant correlation with lesion size (P=0.781) and diameter (P=0.708) meanwhile 69% metabolic activity (SUVmax >2.5) lesions was located on lower limbs in this study. SUVmax correlated significantly with muscle uptake (rs =-0.44, P=0.04). On ROC analysis, the optimum threshold for T/M ratio was >7.42 (AUC=0.965), T/L ratio was >1.837( AUC=0.895), T/F ratio was >13.15 (AUC=0.865). All those ratio showed a significant difference between peripheral nerve sheath tumors (PNSTs) and MPNSTs respectively (P T/M =0.000, P T/L =0.004, P T/F =0.036,). Both T/L ratio >1.84 and T/F ratio >13.15 provided a sensitivity of 100 %, but the specificity (70.6% and 64.7%) were lower for the T/M ratio (88.2%). Conclusion In patients with NF1, quantitative 18F-FDG PET/CT imaging can identify malignant change in neurofibromas with high accuracy. When the metabolic activity (SUVmax >2.5) lesions were superficial,the evaluation of a T/M ratio cut-off value of >7.42 for diagnosing MPNSTs was more suitable Key words: Neurofibromatosis type 1, malignant peripheral nerve sheath tumors, PET, neurofibroma