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

[⁶⁸Ga]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 [⁶⁸Ga]Ga-FAPI-04 could obtain qualified imaging has not been evaluated.

To explore the effect of half-dose [⁶⁸Ga]Ga-FAPI-04 on image quality and tumor detectability in oncology patients.

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 [⁶⁸Ga]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.

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.

Half-dose [⁶⁸Ga]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 [⁶⁸Ga]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.