ABSTRACT
Objective To evaluate the values of the quantitative parameters obtained from 18F-fluorodeoxyglucose (FDG) PET/CT imaging and MRI in prediction of lymph node metastasis (LNM) in patients with rectal cancer.Methods From May 2013 to October 2015,80 patients with rectal cancer (63 males,17 females,age range:37-85 years) that underwent preoperative MRI-diffusion weighted imaging (DWI) and 18 F-FDG PET/CT were enrolled.All patients had pathological results.Auto-segmentation methods of various thresholds were selected to determine the FDG metabolic parameters and whole volume region of interest (ROI) method was performed to measure apparent diffusion coefficient (ADC) in lymph node.Maximum standardized uptake value (SUVmax) =2.5,20％ SUVmax,30％ SUVmax,40％ SUVmax and 50％ SUVmax were selected as the cut-off values (COV),and named as COV1,COV2,COV3,COV4 and COV5,respectively.ROI was drawn automatically and the corresponding mean standardized uptake value (SUVmean) 1-SUVmean5,metabolic tumor volume (MTV) 1-MTV5 and total lesion glycolysis (TLG) 1-TLG5 were calculated.x2 test and logistic regression analysis were used to analyze the associations between the LNM and pathological factors,as well as 18F-FDG metabolic parameters and ADC.Results LNM was found in 55％ (44/80) of the patients.The metabolic parameters of primary tumor in patients with LNM were significantly higher than those in patients without LNM (u values:152.0-555.0,all P＜0.05);the ADC was significantly lower in LNM positive cases than that in LNM negative cases:0.96 (0.93,1.02) × 10-3 mm2/s vs 1.07(1.01,1.11) ×10-3 mm2/s,u=249.0,P＜0.05.Univariate analysis showed that T stage,SUVmax,SUVmean 1-SUVmean 5,MTV1-MTV5,TLG1-TLG5,ADC value were associated with pathologic lymph node involvement (x2 values:7.730-48.198,all P＜0.05).Multivariate analysis indicated that MTV1 (odds ratio (OR)=0.110,95％ CI:0.014-0.840),MTV2 (OR=0.075,95％ CI:0.007-0.852) and ADC (OR=0.034,95％ CI:0.003-0.381) of tumor were significant risk factors associated with LNM (all P＜0.05).The optimal COV of MTV1,MTV2 and ADC were 20.26 cm3,18.47 cm3 and 1.00× 10-3 mm2/s.Conclusion MTV1,MTV2 measured by 18F-FDG PET/CT and ADC measured by MRI-DWI of the primary tumor are risk factors of LNM from rectal cancer,and they may be useful to predict LNM in patients with rectal cancer.