RT Journal Article SR Electronic T1 18F-FDG PET/CT for the detection of superficial malignant peripheral nerve sheath tumors with Neurofibromatosis Type 1, Tumor to muscle ratio is superior to other reference tissues JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 151 OP 151 VO 59 IS supplement 1 A1 Zhao, Xiaobin A1 chen, zhen A1 li, shiwei A1 Chen, Qian A1 Qiao, Zhen A1 zhang, shun A1 zhao, chi A1 zhang, jing A1 Wang, XIn A1 zhao, fu A1 liu, pinan A1 Ai, Lin YR 2018 UL http://jnm.snmjournals.org/content/59/supplement_1/151.abstract AB 151Objectives: 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