Feasibility of acquisitions using total-body PET/CT with a half-dose [ 68 Ga]Ga-FAPI-04 activity in oncology patients

Background [ 68 Ga]Ga-FAPI-04 (gallium-68-labeled fibroblast activation protein inhibitor-04) PET/CT has been widely used in diagnosing malignant tumors. Total-body PET/CT has a long axial field of view and provides higher sensitivity compared to traditional PET/CT. However, whether the reduced injected dose of [ 68 Ga]Ga-FAPI-04 could obtain qualified imaging has not been evaluated. Purpose To explore the effect of half-dose [ 68 Ga]Ga-FAPI-04 on image quality and tumor detectability in oncology patients. Methods A total of twenty-seven patients with tumors or clinically suspected tumors were included, and all patients were scanned with total-body PET/CT after an injected dose of 0.84–1.14 MBq/kg [ 68 Ga]Ga-FAPI-04. All patients obtained superior image quality with 300 s original acquisition time. Images were reconstructed using 180 s, 120 s, 60 s, 40 s, 30 s, 20 s scanning duration by ordered subset expectation maximization algorithm. The subjective image quality of all patients in each time group was scored using 5-point Likert scale. Mediastinal blood pool, liver, spleen, and muscle were analyzed as background using semi-quantitative parameters maximum standardized uptake values (SUV max ), mean standardized uptake values (SUV mean ), standard deviation (SD), and signal to noise ratio (SNR). The lesion detection rate, SUV max , and tumor-to-background ratio (TBR) were calculated for tumors confirmed by pathology. Results The subjective image quality score decreased with the shortening of scanning time; however, both 180 s and 120 s images met the diagnostic requirements in terms of overall quality, lesion conspicuity, and image noise. The SUV max of background increased with the reduction of scanning time, while the SUV mean was relatively stable. With the shortening of scanning time, the SD gradually increased, and the SNR gradually decreased, which was consistent with subjective image quality scores. In 180 s and 120 s images, all 11 primary lesions and 79 metastatic lesions were detected. The SUV max of tumor focus showed an increasing trend as same as the background. Compared with 300 s, the TBR muscle had no statistical difference in 180 s and 120 s. Conclusions Half-dose [ 68 Ga]Ga-FAPI-04 in total-body PET/CT imaging can shorten the acquisition time to 120 s with acceptable subjective image quality and 100% tumor detection rate. Total-body PET/CT imaging with a half-dose [ 68 Ga]Ga-FAPI-04 and reduced acquisition time can be used in radiation-sensitive and poor tolerant to prolong horizontal positioning and waiting time populations such as children and gravidas.