Using ¹⁸F-FDG PET/CT To Estimate The Length Of Gross Tumor And Involved Lymph Nodes In Esophagogastric Junction Carcinoma

Objective:The purposes of this study were to determine the optimal method to estimate length of gross tumor and involved lymph nodes by using 18SF-FDG PET/CT in EGJC verified by pathologic examination.Methods:Twenty patients with newly diagnosed and untreated EGJC were enrolled.All patients underwent preoperative ¹⁸F-FDG PET/CT examination.The length of the gross tumor on PET/CT was measured using different methods:standardized uptake value?SUV?1.5-5.5 in intervals of 1.0,and 10%-50%of maximum standardized uptake value?SUVmax?on ¹⁸F-FDG PET/CT in intervals of 10%,and recorded as L1.0 to L5.0,and L10%to L50%,respectively.We observed the measurable lymph nodes on ¹⁸F-FDG PET/CT and measured the SUVmax of these lymph nodes before operation.Measurements of tumor length were made at operation before the esophagogastric junction specimen was removed?in-vivo,Lvivo?.Each fresh specimen was opened along the longitudinal axis?with care taken not to cut though the tumor?as soon as possible after resection.The free-lying specimen?contracted,Lvitro?was then pinned to a flat board and the longitudinal length was measured A shrinkage ratio formula for the surgical specimen was determined as Lvitro/Lvivo.The pathological length of gross tumor?Lpath?was calculated based on the shrinkage ratio of primary tumor.We observed the measurable lymph nodes on ¹⁸F-FDG PET/CT preoperative,labeled them during operation and examined for pathology.The longitudinal tumor length and lymph nodes were delineated under light microscope.Results:Lpath was?6.87±2.25?cm,the tumor lengths measured by ¹⁸F-FDG PET/CT were as follows:Li.5?8.77±2.05cm?,L2.5?7.56±1.89cm?,L3.5?6.13±1.92cm?,L4.5?5.10±2.23cm?,L5.5?4.70±2.12cm?,L10%?9.10±1.95cm?,L20%?7.56±1.33cm?,L30%?6.61±1.76cm?,L40%?5.64±1.99cm?,L50%?4.88±1.82cm?,L30%was more approximate to Lpath than the other%SUVmax,L2.5 was more approximate to Lpath than the other absolute SUV.Combining correlation coefficients and mean differences between tumor length on PET/CT and pathology,the trend is that L30%seems to be more approximate to Lpath than L2.5.208 lymph nodes were included in our study,158 lymph nodes were negative and 50 lymph nodes were positive.The ROC curve based on the SUVmax of lymph nodes is shown that SUV2.7 was the optimal threshold for detecting lymph node metastases in EGJC.If nodal uptake with SUVmax>2.7 were interpreted as positive,the sensitivity,specificity and accuracy of ¹⁸F-FDG PET/CT in detecting lymph node metastases were 72%,83.54%and 80.77%.Conclusion:The tumor length with 30%SUVmax as the threshold is closest to the actual pathological length of EGJC.The ¹⁸F-FDG PET/CT had the best diagnostic efficiency at the cut-off SUVmax of 2.7 for detecting lymph node metastases in EGJC.