Head To Head Comparison Of ¹⁸F-FAPI Versus ¹⁸F-FDG PET/CT In The Evaluation Of Diffuse Gastric Cancer

Purpose Diffuse gastric cancer（DGC）is an aggressive pathological type of gastric cancer with poor prognosis.Early staging and accurate diagnosis are crucial for determining a suitable treatment strategy and improving the prognosis of patients with DGC.Previous studies have found that ¹⁸F-FDG PET/CT has limitations in the diagnosis and staging of DGC.This study aimed to evaluate the clinical staging or restaging performance of ¹⁸F-FAPI PET/CT in DGC compared to that of ¹⁸F-FDG PET/CT.Methods A total of 30 participants with histologically proven DGC who underwent contemporaneous ¹⁸F-FDG and ¹⁸F-FAPI PET/CT within one week from January 2022 to October 2022 at the Affiliated Cancer Hospital and Institute of Guangzhou Medical University were analyzed.The maximum standardized uptake value（SUVmax）and tumor-to-background ratio（TBR）value were measured from the primary and metastatic lesions,which were compared for paired positive lesions between both modalities by using the Wilcoxon signed-rank test.The sensitivity,specificity,and accuracy of ¹⁸F-FDG and ¹⁸F-FAPI PET were calculated and compared using Mc Nemar’s test to evaluate their diagnostic performance.A p value<0.05 was considered statistically significant.Staging orRestaging was evaluated by both the two imaging modalities and compared with the final clinical staging,to evaluate the accuracy of two modalities in disease staging.Results1)Compared to ¹⁸F-FDG PET/CT,¹⁸F-FAPI PET/CT showed higher sensitivity and accuracy in detecting primary lesions[93.8%（0.677-0.997）vs.68.8%（0.415-0.879）and 96.7%（29/30）vs.66.7%（20/30）],lymph node metastases[84.3%（0.774-0.895）vs.25.5%（0.190-0.333）and89.9%（277/308）vs.55.8%（172/308）],and distant metastases[（100%（0.983-1.0）vs.34.8%（0.292-0.407）and 99.0%（307/310）vs.39.7%（123/310）],and the differences of the sensitivity and accuracy of two imaging modalities were statistically significant（P<0.05）.2）In semiquantitative analysis of lesions,the SUVmax and TBR of ¹⁸F-FAPI PET/CT were significantly higher than those of ¹⁸F-FDG PET/CT in the primary tumor（SUVmax,P=0.0030;TBR,P=0.0010）,lymph node metastases（both P<0.0001）,peritoneal metastases（both P<0.0001）,liver metastases（SUVmax,P=0.0276;TBR,P<0.0001）,lung metastases（SUVmax,P=0.0078;TBR,P=0.0078）,bone metastases（both P<0.0001）,muscle metastases（SUVmax,P=0.0020;TBR,P=0.0273）,and pleura metastases（SUVmax,P=0.0469;TBR,P=0.1950）.In addition,¹⁸F-FAPI PET/CT showed higher SUVmax in uterus or ovary metastases（P=0.0312）than that of ¹⁸F-FDG PET/CT,while there was no statistically significant difference in TBR（p=0.6250）between two modalities.3)In staging or restaging of the disease,¹⁸F-FAPI PET/CT changed tumor staging or restaging in 11 participants（36.7%,11/30）.Furthermore,the peritoneal cancer index（PCI）score derived from ¹⁸F-FAPI PET/CT was higher than that derived from ¹⁸F-FDG PET/CT.Conclusion ¹⁸F-FAPI PET/CT demonstrated better staging or restaging performance than ¹⁸F-FDG PET/CT in the evaluation of primary tumors,lymph nodes and especially peritoneal metastases,suggesting that it can be used for staging or restaging in patients with DGC.