Purpose To explore the diagnostic efficacy of 99Tcm labeled fibroblast activation protein inhibitor(FAPI)SPECT/CT for metastatic lesions in advanced colorectal cancer and its impact on decisions regarding immunotherapy,and to compare it with 18F-FDG PET/CT.Materials and Methods A total of 34 patients with advanced colorectal cancer who underwent both 99Tcm-FAPI SPECT/CT and 18F-FDG PET/CT imaging from August 2022 to November 2023 in Fuzhou University Affiliated Provincial Hospital were prospectively included.The gold standard was based on biopsy or clinical and imaging follow-up results.Chi-square tests and rank sum tests were used to compare differences between the groups.Results Among the 34 patients,17 patients subsequently received immunotherapy.The uptake of 99Tcm-FAPI was significantly higher than that of 18F-FDG for the primary tumor site(Z=-2.389,P=0.017),peritoneal metastasis(Z=-2.497,P=0.013)and liver metastasis(Z=-0.106,P=0.015).The diagnostic efficacy of 99Tcm-FAPI SPECT/CT for patients with peritoneal metastasis was superior to that of 18F-FDG PET/CT(χ2=4.65,P=0.033).Metastatic lesions that did not uptake 99Tcm-FAPI had a better clinical prognosis after immunotherapy(χ2=11.839,P=0.006),and maximum standardized uptake value(SUVmax)-FDG/SUVmax-FAPI ratio was a promising predictive factor for a better prognosis after immunotherapy,with an optimal cut-off value of 5.04.Conclusion 99Tcm-FAPI SPECT/CT has superior diagnostic efficacy for peritoneal metastasis in advanced colorectal cancer compared with 18F-FDG PET/CT.SUVmax-FDG/SUVmax-FAPI ratio is a promising radiomic parameter for predicting patient prognosis after immunotherapy,which can help guide clinical decision-making further.

Purpose To explore the diagnostic efficacy of 99Tcm labeled fibroblast activation protein inhibitor(FAPI)SPECT/CT for metastatic lesions in advanced colorectal cancer and its impact on decisions regarding immunotherapy,and to compare it with 18F-FDG PET/CT.Materials and Methods A total of 34 patients with advanced colorectal cancer who underwent both 99Tcm-FAPI SPECT/CT and 18F-FDG PET/CT imaging from August 2022 to November 2023 in Fuzhou University Affiliated Provincial Hospital were prospectively included.The gold standard was based on biopsy or clinical and imaging follow-up results.Chi-square tests and rank sum tests were used to compare differences between the groups.Results Among the 34 patients,17 patients subsequently received immunotherapy.The uptake of 99Tcm-FAPI was significantly higher than that of 18F-FDG for the primary tumor site(Z=-2.389,P=0.017),peritoneal metastasis(Z=-2.497,P=0.013)and liver metastasis(Z=-0.106,P=0.015).The diagnostic efficacy of 99Tcm-FAPI SPECT/CT for patients with peritoneal metastasis was superior to that of 18F-FDG PET/CT(χ2=4.65,P=0.033).Metastatic lesions that did not uptake 99Tcm-FAPI had a better clinical prognosis after immunotherapy(χ2=11.839,P=0.006),and maximum standardized uptake value(SUVmax)-FDG/SUVmax-FAPI ratio was a promising predictive factor for a better prognosis after immunotherapy,with an optimal cut-off value of 5.04.Conclusion 99Tcm-FAPI SPECT/CT has superior diagnostic efficacy for peritoneal metastasis in advanced colorectal cancer compared with 18F-FDG PET/CT.SUVmax-FDG/SUVmax-FAPI ratio is a promising radiomic parameter for predicting patient prognosis after immunotherapy,which can help guide clinical decision-making further.