The role of 99mTc-HFAPi SPECT/CT in patients with malignancies of digestive system: first clinical experience

Abstract

Background Recently, PET/ CT imaging with radiolabelled FAP inhibitors (FAPIs) has been widely evaluated in diverse diseases. However, rare report has been published using SPECT/CT, a more available imaging method, with 99mTc-labelled FAPI. In this study, we evaluated the potential effect of 99mTc-HFAPi in clinical analysis for digestive system tumours. Methods This is a single-centre prospective diagnostic efficiency study (Ethic approved No.: XJTU1AF2021LSK-021 of First Affiliated Hospital of Xi’an Jiaotong University and ChiCTR2100048093 of Chinese Clinical Trial Register). 40 patients with suspected or confirmed digestive system tumours underwent 99mTc-HFAPi SPECT/CT between January through June 2021. For dynamic biodistribution and dosimetry estimation, whole-body planar scintigraphy was performed at 10, 30, 90, 150, and 240 min post-injection. Optimal acquisition time was considered at 60–90 min post-injection and semi-quantified using SUVmax and T/B ratio. The diagnostic performance of 99mTc-HFAPi were calculated and compared with those of contrast-enhanced CT (ceCT) using McNemar test, and the changes of tumour stage and oncologic management were recorded. Results Physiological distribution of 99mTc-HFAPi was observed in the liver, pancreas, gallbladder, and to a lesser extent in the kidneys, spleen and thyroid. The diagnostic sensitivity of 99mTc-HFAPi for non-operative primary lesions was similar to that of ceCT (94.29% [33/35] vs 100% [35/35], respectively; P = 0.5); in local relapse detection, 99mTc-HFAPi was successfully detected in 100% (n = 3) of patients. In the diagnosis of suspected metastatic lesions, 99mTc-HFAPi exhibited higher sensitivity (89.66% [26/29] vs 68.97% [20/29], respectively, P = 0.03) and specificity (97.9% [47/48] vs 85.4% [41/48], respectively, P = 0.03) than ceCT, especially with 100% (24/24) specificity in the diagnosis of liver metastases, resulting in 20.0% (8/40) changes in TNM stage and 15.0% (6/40) changes in oncologic management. Conclusion 99mTc-HFAPi demonstrates a greater diagnostic efficiency than ceCT in the detection of distant metastasis, especially in identifying liver metastases.