Values Of ¹⁸F-FAPI-42 PET/CT In Diagnosis Of Primary And Metastatic Peritoneal Carcinomatosis:Head-to-head Comparison With ¹⁸F-FDG

ObjectiveTo evaluate the values of ¹⁸F-FAPI PET/CT in the qualitative and quantitative diagnosis and stratification of primary and metastatic peritoneal carcinomatosis（PC）.Method:A total of 76 suspected PC patients were selected and divided into the case group（PC patients,42 cases）and control group（non-PC patients,34 cases）according to histopathological findings.¹⁸F-FAPI and ¹⁸F-FDG PET/CT were performed in all patients with an interval time shorter than 14 days.The positive criterion was the radioactive uptake of ¹⁸F-FDG or ¹⁸F-FAPI-42 in the lesion exceeding that in the adjacent background organization.Peritoneal carcinomatosis index（PCI）was quantified by evaluating the lesion size in the 13 regions.The detection rate of PC was compared between ¹⁸F-FDG and ¹⁸F-FAPI PET/CT,as well as their maximum standardized uptake value(SUV_max)and PCI.The values of diagnosing PC and its lesion were compared between ¹⁸F-FDG and ¹⁸F-FAPI PET/CT.The consistency was evaluated between PCI quantified by ¹⁸F-FDG or ¹⁸F-FAPI PET/CT and that quantified during operation.Results:1.For 42 cases,global and stratification comparisons（female/male,>61years/≤61 years and nodular PC/diffuse PC）showed that the detection rates of PC of¹⁸F-FAPI PET/CT were statistically higher than those of ¹⁸F-FDG PET/CT except for mucinous primary tumors and nodular PC（global:100.0%vs73.8%,female:100.0%vs79.3%,male:100.0%vs61.5%,>61 years:100.0%vs66.7%,≤61 years:100.0%vs81.0%,and diffuse PC:100.0%vs69.0%;P均<0.05）.2.For 42 cases,both global and stratification comparisons showed that the SUVs_max of ¹⁸F-FAPI PET/CT were significantly higher than those of ¹⁸F-FDG PET/CT（global comparison:8.39±4.48 vs 4.45±3.4）;for different primary tumors,the SUVs_maxof ¹⁸F-FAPI PET/CT were significantly higher than those of ¹⁸F-FDG PET/CT in gastric cancer（8.71±3.57 vs3.08±3.41）and ovarian cancer（10.84±4.65vs5.47±2.87）,and there were no significant differences in colorectal cancer and other tumors,possibly due to the small sample size.3.For 42 cases,the PCI of ¹⁸F-FAPI PET/CT was significantly higher than that of ¹⁸F-FDG PET/CT（18.66±11.99 vs 12.36±13.22）,and stratification comparisons did not demonstrate the significant differences,as well as comparisons in different primary tumors,possibly due to the small sample size.4.For PC patients with the same PCIs,the PC patients with ovarian cancer as theprimary tumor demonstrated a higher SUVmax in ¹⁸F–FAPI PET/CT than that in¹⁸F-FDG PET/CT,and other tumors demonstrated no significant differences between¹⁸F–FAPI and ¹⁸F-FDG PET/CT.5.The areas under curve（AUC）of ¹⁸F-FAPI and ¹⁸F-FDG PET/CT applied in predicting PC were 1.000[standard error（SE）:0.000,95%confidence interval（CI）:1.000～1.000]and 0.838（SE:0.051,95%CI:0.738～0.939）,respectively,and the AUC of ¹⁸F-FAPI was significantly higher than that of ¹⁸F-FDG（Z=3.176,P<0.001）.Moreover,the sensitivity,accuracy and negative predictive value of ¹⁸F-FAPI were significantly higher than those of ¹⁸F-FDG（P<0.05）.6.Among 13 nodular PC patients（84 nodules）,¹⁸F-FAPI PET/CT detected 13positive patients（83 nodules）,and¹⁸F-FDG PET/CT detected 11 positive patients（47nodules）.The sensitivity of ¹⁸F-FAPI PET/CT was significantly higher than that of¹⁸F-FDG PET/CT（χ²=44.074,P<0.001）.7.The intraclass correlation coefficients（ICCs）between PCI quantified by ¹⁸F-FDG,¹⁸F-FAPI PET/CT and PCI quantified during operation or the follow-up were0.902（95%CI:0.325～0.964）and 0.968（95%CI:0.753～0.997,P<0.001）,respectively.Conclusion:The effects of ¹⁸F-FAPI PET/CT applied in qualitative and quantitative diagnosis and grading of PC were better than ¹⁸F-FDG although a few indexes were not statistically different due to the small sample size.Therefore,it could be applied in clinic.In the next step,we will further verify the application value of ¹⁸F-FAPI PET/CT through a big sample size.