Objective To explore the detection scheme of ambient dose equivalent rates around EVISION-720 mobile head cone-beam CT (EVISION-720 mobile CT) and analyze the spatial distribution characteristics of its radiation dose field.

Methods Three planes at a height of 0.3, 0.8, and 1.3 m from the floor were selected in the counterclockwise direction of 0° (in front of EVISION-720 mobile CT), 45°, 90°, 135°, 180°, 225°, 270°, and 315°. Using the scanning center as the zero-point position, the detection sites were arranged at a distance of 1–10 m from the surface of EVISION-720 mobile CT at an interval of 1 m. A radiation dosimeter was used to measure the ambient dose equivalent rates from the detection sites (operation sites set at the time of clinical application) at 6 m from the surface of EVISION-720 mobile CT under rated parameters of 110 kV/20 mA, 90 kV/40 mA, and 70 kV/60 mA. In addition, ambient dose equivalent rates were measured at all detection sites under rated parameter of 110 kV/20 mA. Measurements of the three planes at a height of 0.3, 0.8, and 1.3 m from the floor under rated parameter of 110 kV/20 mA were plotted for 1, 5, 10, 20, 40, and 100 μSv/h isodose curves, that is, radiation dose field distribution map. The Wilcoxon test was used for comparison among ambient dose equivalent rates at the same heights from the floor under the different rated parameters, and ambient dose equivalent rates at different heights from the floor under the same rated parameters, respectively.

Results Under the three rated parameters, the measurement results of ambient dose equivalent rate gradually increase with the increase of tube voltage, but they do not change with the change of height from the floor. Moreover, the ambient dose equivalent rate in the 0° direction under rated parameter of 110 kV/20 mA was the highest ((34.44±0.09) μSv/h). At the same height from the floor under different rated parameters, the differences in ambient dose equivalent rates were statistically significant (Z=−2.527 to 2.524, all P<0.05). Furthermore, the differences in ambient dose equivalent rates at different heights from the floor under the same rated parameter are not statistically significant (Z=−1.690 to −0.169, all P>0.05). Based on the radiation dose field of EVISION-720 mobile CT, the "symmetry" and "triangle" distribution are obtained: the ambient dose equivalent rate in the 135° and 225° direction was the lowest, and the ambient dose equivalent rate in the 0° direction was the highest.

Conclusions The radiation dose field around EVISION-720 mobile CT presents a symmetry distribution on both sides and a triangle distribution in front and at back of the equipment. In addition, the ambient dose equivalent rate in the front is higher than that on both sides and at the back. Therefore, medical institutions should strengthen radiation protection management in front of the equipment.