Objective To investigate the value of 18F-FDG PET/CT combined with conventional imaging modalities in the evaluation of the depth of tumor invasion,regional lymph node metastasis,distant organ and lymph node metastasis(TNM staging),and the adjacent structure invasion of rectal cancer.Meth-ods Fifty-four patients(28 males,26 females,age(65.8±11.0)years)with pathologically confirmed rec-tal cancer admitted to the Affiliated Qingdao Central Hospital of Qingdao University between September 2019 and June 2021 were retrospectively analyzed.18F-FDG PET/CT examination,conventional imaging modali-ties including high-resolution MRI(HR-MRI),chest CT plain scan,upper abdominal MRI or CT plain scan+enhanced examination were performed within 2 weeks before or after the rectal cancer being confirmed.The TNM staging and adjacent structural invasions including circumferential resection margin(CRM),ex-tramural vascular invasion(EMVI),anal sphincter complex involvement were evaluated by 18 F-FDG PET/CT and conventional imaging modalities separately or in combination,and those results based on imaging were compared with the pathological results or clinical follow-up results.X2 test was used to compare the differences of diagnostic sensitivity,specificity and accuracy between the 18F-FDG PET/CT or conventional imaging modalities and combined examination.Results The accuracy for T staging and the sensitivity and accuracy for N staging of the combined examination were 96.30％(52/54),98.65％(73/74)and 93.91％(185/197),respectively,which were significantly higher than those of 18F-FDG PET/CT(85.19％(46/54),66.22％(49/74),81.73％(161/197);x2 values:3.97,26.88,13.66,all P＜0.05).The specificity(91.06％,112/123)and accuracy of the combined examination for N staging were higher than those of the conventional imaging modalities(77.24％(95/123),83.76％(165/197);x2 values:8.81,10.23,both P＜0.05).The sensitivity and accuracy of the combined examination for M staging were higher than those of the conventional imaging modalities(97.01％(65/67)vs 73.13％(49/67),95.95％(71/74)vs 68.92％(51/74);X2 values:15.05,18.66,both P＜0.001).The sensitivities of the combined examination in evaluating CRM and EMVI were 100％(22/22)and 95.00％(19/20),and the accuracies were 98.15％(53/54)and 96.30％(52/54),all of which were higher than those of 18F-FDG PET/CT(CRM:54.55％(12/22),74.07％(40/54);EVMI:30.00％(6/20),74.07％(40/54);x2 values:12.94,13.08,18.03,10.56,all P＜0.01).The accuracy of the combined examination in evaluating EMVI was higher than that of the conven-tional imaging modalities(85.19％(46/54);x2=3.97,P=0.046).Conclusion 18F-FDG PET/CT com-bined with conventional imaging modalities can improve the diagnostic efficacy for TNM staging and assess-ment of adjacent structural invasion in rectal cancer.
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