The Application Of ¹⁸F-FDG PET/CT Imaging With Metabolic Parameters In Gastric Malignant Tumors

Objective Gastric malignant tumor is one of the serious disease that threaten the public health.Accurate diagnosis and finding effective indicators for evaluating the patients’prognosis and curative effect is the key point to make the best treatment strategy and improve the quality of life of patients.In this study,we retrospectively summarized and analyzed the clinical data and metabolic parameters of ¹⁸F-FDG PET/CT in patients with suspected different types of gastric malignant tumors.We originally compared the efficacy of different metabolic parameters（MTV,TLG）which obtained by different SUVmax thresholds,and analyzed the relationship between the best metabolic parameters（SUVmax,MTV,TLG,MTVwb,TLGwb）and clinical factors.We also explored the clinical value of metabolic parameters in the diagnosis and prognosis of gastric malignant tumors,which could provide a theoretical basis for prognostic evaluation and promote the clinical application of metabolic parameters of ¹⁸F-FDG PET/CT in precise diagnosis and therapy of gastric malignant tumor.Methods We retrospectively analyzed the data of the patients who were first diagnosed as gastric malignant tumor and underwent ¹⁸F-FDG PET/CT before first-line treatment in our hospital from May 8,2012 to August 29,2019.All the patients were pathologically confirmed as gastric cancer（GC）and primary gastric lymphoma（PGL）.The clinical data and follow-up results（survival or death,disease with progression or no progression）by telephone were recorded.A total of 77 cases were enrolled in this study after strict inclusion and exclusion criteria.Visual analysis and fixed threshold method were used in imaging analysis.Definition of positive imaging was defined as follow:1.Visual method combined with fixed threshold SUVmax method:combined the shape,location,concentration degree and uniformity of FDG of the lesion with the findings of CT,i.e.the focal increased ¹⁸F-FDG uptake along the local thickened gastric wall protruding to the gastric cavity was observed as positive.The parameters including SUVmax,2.5 by SUVmax,40%SUVmax and 60%SUVmax were recorded separately as threshold.2.Criterion of regional lymph node and distant metastasis:the positive results were displayed as local abnormal uptake of ¹⁸F-FDG combined with the abnormal shape,size,density on CT scan.ROIs were used to form the metabolic parameters（SUVmax,MTV,TLG）of primary tumor and whole body tumor metabolic parameters（MTVwb,TLGwb）,and the corresponding parameters defined by different thresholds were measured and calculated.After the normal distribution test of the data,the independent sample nonparametric test was used to analyze the differences of parameters obtained by different SUVmax thresholds,the relationship between clinical factors and tumor metabolic parameters,and then the statistically significant clinical factors were analyzed by multiple linear regression analysis.According to the follow-up results,the best threshold of ¹⁸F-FDG PET/CT metabolic parameters for predicting OS and PFS in patients with gastric malignant tumor was obtained by ROC curve.The median survival time was estimated by Kaplan-Meier method and the survival curve was drawn,and Log-rank method was used to test the difference of survival curve between group.Univariate and multivariate Cox proportional hazard regression models were used to screen the related independent prognostic factors by positive stepwise multiple regression analysis,and the risk ratio（HR）and its 95%confidence interval（95%CI）were estimated.P<0.05 was considered as statistically significant.Results 1.The semi-quantitative parameters obtained by using thresholds as 2.5SUVmax,40%SUVmax and 60%SUVmax of ROIs were statistically different.The results showed that the value of MTV and TLG were significant different among the three groups（P<0.05）.Pairwise comparison found that there was no statistical difference between2.5SUVmax and 40%SUVmax groups ONLY.2.There were significant differences in SUVmax,MTV and TLG between GC and PGL（P<0.05）.The median SUVmax,MTV and TLG of GC and PGL were 6.83,17.70cm³,72.96g and 18.63,41.99cm³,402.9g,respectively.3.In GC patients,there was no significant difference of the metabolic parameters among different age,sex and differentiation groups（P>0.05）,but significant difference in SUVmax of different primary tumor sites was observed（H=6.595,P=0.037）.Also,the SUVmax MTVwb and TLGwb among different clinical stages were significantly different（H=12.266,P=0.001）.4.According to the optimist critical threshold,the metabolic parameters of patients with GC were divided into higher value group and lower value group.For OS,the AUC of SUVmax was the largest（AUC=0.74）;while for PSF,the largest AUC was from TLG（AUC=0.72）.There were also significant differences in SUVmax,TLG,MTVwb and TLGwb between the 2 groups in not only median OS but also PFS.5.In PGL patients,the metabolic parameters were divided into higher value group and lower value group according to the optimist critical threshold.The AUC of MTVwb was the largest in both OS and PFS（AUC=0.81 and 0.77）.For OS,the MTV,MTVwb and TLGwb were significantly different between the 2 groups（P<0.05）.For PFS,the SUVmax,TLG,MTVwb and TLGwb was statistically significant in the 2 groups（P<0.05）.6.In GC patients,the univariate analysis showed that tumor biomarker CEA,clinical stage,SUVmax,TLG,MTVwb and TLGwb were prognostic risk factors for OS and PFS.The level of serum CA19-9 and MTV were the only prognostic risk factors for PFS（P=0.041,0.024）,but not for OS.Multivariate analysis showed that clinical stage and SUVmax were independent prognostic factors for OS（P=0.000,0.000）,meanwhile the level of serum CEA,clinical stage and SUVmax were independent prognostic factors for PFS（P=0.033,0.003,0.018）.7.In PGL patients,the univariate analysis showed that Ann Arbor stage,MTV,TLG and TLGwb were prognostic risk factors for OS and PFS.MTVwb was one prognostic risk factor for OS（P=0.047）,but not for PFS（P=0.078）.TLGwb were prognostic risk factors for OS and While,SUVmax was not a prognostic risk factor for not only OS but also PFS（P=0.140,0.171）.Multivariate analysis showed that TLG was an independent prognostic factor for OS（HR 95%CI:1.001（1.000-1.001）,P=0.010）and MTV was an independent prognostic risk factor for PFS（HR 95%CI:1.011（1.001-1.021）.P=0.036）.Conclusion 1.The PET/CT metabolic parameters（SUVmax,MTVwb,TLGwb）were statistically different among GC patients at different clinical stages.The parameters of advanced GC were higher than those of early GC.2.The metabolic parameters of ¹⁸F-FDG PET/CT（SUVmax,TLG,MTVwb,TLGwb）provided a reliable differential diagnosis of GC and PGL.The higher the metabolic parameter value,the greater the possibility of PGL.3.The level of serum CEA,clinical stage,SUVmax,TLG,MTVwb and TLGwb were prognostic factors for OS in GC patients,and clinical stage and SUVmax were independent prognostic factors for OS.The level of serum CEA,CA19-9,clinical stage,MTV,SUVmax,TLG,MTVwb and TLGwb were prognostic factors for PFS in GC patients,and the level of CEA and SUVmax were independent prognostic factors for PFS.4.Ann Arbor stage,MTV,MTVwb and TLGwb were prognostic factors for OS in PGL patients,and TLG was an independent risk factor for prognosis.For PFS,Ann Arbor stage,MTV,TLG and TLGwb were prognostic factors,and MTV was an independent risk factor for prognosis.