Prospective Study Comparing [^99mTc]Tc-DP-FAPI Quantitative SPECT/CT with [⁶⁸Ga]Ga-FAPI-04 PET/CT in Patients with Gastrointestinal Tumors

Over the past decade, [⁶⁸Ga]Ga-FAPI-04 positron emission tomography (PET)/CT imaging has been widely used for the treatment of various tumors. However, the application of ^99mTC-labeled fibroblast activation protein inhibitors in tumors has been less studied. Our team previously demonstrated the safe biological distribution of [^99mTc]Tc-DP-FAPI in the human body. Based on this, this study reports the accuracy of [^99mTc]Tc-DP-FAPI in the imaging diagnosis of gastrointestinal tumors and compares it with that of [⁶⁸Ga]Ga-FAPI-04 to evaluate the differences. A total of 24 patients with clinically diagnosed gastrointestinal tumors were prospectively included. All patients received [^99mTc]Tc-DP-FAPI quantitative SPECT/CT imaging on the first day and [⁶⁸Ga]Ga-FAPI-04 PET/CT imaging on the second day. And the effectiveness of the two imaging probes in detecting suspicious lesions was analyzed and compared. The primary tumors of all 24 patients were well detected by two imaging probes, and the sensitivity of [^99mTc]Tc-DP-FAPI and [⁶⁸Ga]Ga-FAPI-04 to the primary lesions was 100%. [^99mTc]Tc-DP-FAPI examined 21 lymph nodes with a sensitivity and specificity of 32.8% and 10.9%, and [⁶⁸Ga]Ga-FAPI-04 detected 57 lymph nodes with a sensitivity and specificity of 89.1% and 67.2%, respectively. Three distant metastases were detected by [^99mTc]Tc-DP-FAPI and nine metastases by [⁶⁸Ga]Ga-FAPI-04. The study showed that [^99mTc]Tc-DP-FAPI is highly sensitive to detecting primary lesions of gastrointestinal tumors. Compared with [⁶⁸Ga]Ga-FAPI-04, [^99mTc]Tc-DP-FAPI has the same sensitivity in detecting primary tumors but has certain limitations in detecting metastases. [^99mTc]Tc-DP-FAPI is of great value for preliminary screening of tumor lesions and early diagnosis of disease in patients who are suspected of having gastrointestinal tumors.