Spatial-temporal distribution characteristics and analysis of the peripheral dose equivalent rate around patients undergoing 68Ga-FAPI PET/CT

Objective To quantify the spatial-temporal distribution characteristics of the peripheral dose equivalent rate around patients undergoing 68Ga-FAPI PET/CT, and to provide a basis for optimizing radiation protection strategies.Methods A total of 30 patients who underwent 68Ga-FAPI PET/CT examination were included. The peripheral dose equivalent rate at distances of 0.25, 0.5, 1, 2, 3, and 4 m from the patient were measured at 0, 0.5, 1, 1.5, 2, and 3 h after the injection of the radiopharmaceuticals. The relationship between the dose equivalent rate and the distance was fitted by the inverse ratio law to the power of 1.5, and the exponential decay model was used to analyze the variation law of the dose equivalent rate with time, and the radiation doses level received by the surrounding personnel was estimated.Results The peripheral dose equivalent rate significantly decayed with the increase of distance, Within a distance of 3 meters, conforming to the inverse ratio law to the power of 1.5, within 0 to 3 hours, the variation range of the fitting constant k value is from 8.98 to 1.67. The peripheral dose equivalent rate decayed exponentially with time, with a decay constant λ of 0.74 h−1 at a distance of 1 m from the patient, resulting in an effective half-life of 56 min. Within 3 h after the injection of the radiopharmaceuticals, At 0.25 m, the dose rates was the highest at 0 h, reaching a normalized value of (68.05±5.94) μSv·h-1(100MBq)-1; it decreased to (15.61±1.86) μSv·h-1(100MBq)-1 at 3 h. The effective doses received by the positioning technician, the family members contacted during the day, the family members sleeping in the same bed at night, and the colleagues at the workplace were 0.40, 14.14, 87.94, and 14.27 μSv per patient respectively.Conclusions The peripheral dose equivalent rate around patients undergoing 68Ga-FAPI PET/CT decreases rapidly with distance and time, and the public exposure level caused by patients to the surrounding personnel is lower than the effective dose constraint value stipulated by the national standard.