18F-FDG PET/CT role in staging of gastric carcinomas: comparison with conventional contrast enhancement computed tomography.

Aim: to evaluate the role of 18F-FDG PET/CT in staging gastric carcinoma comparing it with Contrast Enhancement Computed Tomography (CECT) and if morphological and functional parameters might give a contribution. Materials and methods: This retrospective study included 45 patients who underwent whole body CECT and 18F-FDG PET/CT before any treatment. We calculated CECT and 18F-FDG PET/CTsensitivity, specificity, accuracy, positive and negative predictive values (PPVand NPV) for gastric, lymphnode and distant localizations; furthermore we compared the two techniques by McNemar test. Linear regression was performed to evaluate SUVmax and SUVmean in relation to gastric lesion size. The role of 18F-FDG PET/CT semiquantitative parameters in relation to histotype, grading and site of gastric lesions were evaluated by ANOVA test. Results: sensitivity, specificity, accuracy, PPVand NPVof CECT and 18F-FDG PET/CT for gastric lesion were respectively 92.11%, 57.14%, 86.66%, 92.11%, 57.14% and 81.58%, 85.71%, 82.22%, 96.88%, 46.15%. No differences were identified between the 2 techiques about sensitivity and specificity. No stastistical differences were observed between PET parameters and histotype, grading and site of gastric lesion. The mean value of the maximum diameter was 52.59 mm (range 4 - ≥100). Considering 30 mm, as a threshold value for maximum diameter we divided patients in 2 groups: size ≤ 30 mm and size > 30. In 15/45 pts size was ≤ 30 mm and 18F-FDG PET/CT sensitivity and specificity resulted respectively 33.33% (95%CI: 7.88% to 69.93%) and 83.33% (95%CI: 36.10% to 97.24%). In 30/45 pts size was > 30 mm and 18F-FDG PET/ CT sensitivity and specificity resulted respectively 96.55% (95%CI: 82.17% to 99.42%) and 100% (95%CI: 16.55% to 100%). SUVmax and SUVmean resulted positively related to lesion dimension (SUV max=3.53+0.11*lesion size, F=8.91, p=0.005; SUV mean=1.99+0.06*lesion size, F=7.07 p=0.01) No stastistical differences were observed between PET parameters and histotype, grading and site of gastric lesion. The results of CECT and 18F-FDG PET/CT about lymphnode involvement were 70.83%, 61.90%, 66.66%, 68%, 65% and 58.33%, 95.24%, 75.55%, 93.33%, 66.67%. The results of CECT and 18F-FDG PET/CT about distant metastases were 80%, 62.86%, 66.66%, 38.10%, 91.67% and 60%, 88.57%, 82.22%, 60%, 88.57%. 18FDG PET/CT specificity was significantly higher both for lymphnode and distant metastases.Conclusions: the 18F-FDG PET/CT is a useful tool for the evaluation of gastric carcinoma to detect primary lesion, lymphnode and distant metastases using one single image whole-body technique. Integration of CECT with 18F-FDG PET/CT permits a more valid staging in these patients.