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移动式CT可应用于床旁CT检查等普通CT难以使用的条件下,被广泛应用于重症监护室[1-2]、手术室[3]、野战医院[4]等场所,减少了搬运的麻烦,并降低了外出对重症患者造成的风险[5],为医学诊断和治疗提供了便利,为更好地服务重症、急症患者提供了保障,更是为院外诊疗提供了丰富和适用的放射诊断设备。移动式CT还可用于传染病爆发期间需要严格隔离感染者的检查和诊断,可以防止交叉感染,减少传染病的传播[6]。移动式CT设备机架的周围剂量当量率远低于常规CT,对陪检者、公众和医护人员的辐射影响相对较小,更利于野外急救场所、方舱医院、临时放射科等临时放射工作场所使用[7]。对于多用于无屏蔽机房或辐射屏蔽设施缺乏场所的移动式CT,其曝光时的辐射剂量场分布的研究对于工作场所控制区和监督区的划分具有重要的指导作用,对于辐射安全管理[8]、职业照射和公众照射的控制具有重要作用。目前,国内外对于移动式CT辐射剂量场分布的测量方案的研究较少[9]。本研究旨在通过对国内新研发的平板探测器EVISION-720型移动式头部锥形束CT(简称EVISION-720型移动式CT)不同点位的周围剂量当量率进行测量,明确该移动式CT的辐射防护方案,并为其辐射屏蔽设计和现场使用条件下防护设施的设置提供技术指导。
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3种额定参数及3种距地面高度处,距离EVISION-720型移动式CT表面6 m处的周围剂量当量率测量结果见表1,配对Wilcoxon秩和检验的结果见表2和表3。由表1~3可知,在110 kV/20 mA额定参数下,0°方向上即扫描中心孔上的周围剂量当量率最大,为(34.44±0.09) μSv/h;仅有270°方向上的检测位点在90 kV/40 mA额定参数下、距地面0.3 m高度处的周围剂量当量率略高于110 kV/20 mA额定参数下的测量结果,其余检测位点,在90 kV/40 mA和70 kV/60 mA额定参数下,距地面不同高度处的测量结果均低于110 kV/20 mA额定参数下的测量结果;周围剂量当量率基本上随3种额定参数中管电压的增大逐渐增大,而不随测量处距地面高度的变化而变化。在不同额定参数下,距地面相同高度处的周围剂量当量率的差异均有统计学意义(Z=−2.527~2.524,均P<0.05)。在相同额定参数下,距地面不同高度处的周围剂量当量率的差异均无统计学意义(Z=−1.690~−0.169,均P>0.05)。
额定参数 距地面高度(m) 检测点位角度 0° 45° 90° 135° 180° 225° 270° 315° 110 kV/20 mA 0.3 34.44±0.09 12.04±0.37 12.56±0.29 1.23±0.04 9.66±0.11 1.43±0.05 4.70±0.05 9.58±0.03 0.8 28.98±0.05 11.29±0.07 8.69±0.06 1.53±0.03 6.05±0.02 1.54±0.02 9.91±0.06 9.74±0.07 1.3 28.98±0.06 11.40±0.57 12.85±0.04 1.72±0.10 6.55±0.11 1.63±0.05 10.42±0.09 9.26±0.09 90 kV/40 mA 0.3 25.20±0.41 7.93±0.10 8.23±0.07 0.76±0.03 2.01±0.10 0.52±0.05 5.04±0.10 5.46±0.11 0.8 22.60±0.33 7.31±0.12 5.88±0.19 0.73±0.04 2.00±0.16 0.69±0.04 5.63±0.13 4.87±0.17 1.3 21.84±0.42 6.64±0.20 7.81±0.25 0.78±0.05 1.93±0.12 0.69±0.05 5.96±0.19 5.12±0.07 70 kV/60 mA 0.3 9.74±0.20 2.77±0.11 0.92±0.04 0.13±0.02 0.32±0.04 0.19±0.02 0.60±0.04 2.12±0.05 0.8 8.23±0.09 2.69±0.20 0.79±0.07 0.24±0.02 0.35±0.04 0.17±0.02 0.63±0.10 1.80±0.15 1.3 7.81±0.13 2.69±0.20 0.93±0.07 0.18±0.03 0.39±0.05 0.19±0.02 0.71±0.09 1.83±0.10 表 1 3种额定参数及3种距地面高度处距离EVISION-720型移动式头部锥形束CT表面6 m处的周围剂量当量率(
,μSv/h)$ \bar x \pm s $ Table 1. Ambient dose equivalent rates at six meters from the surface of EVISION-720 mobile head cone-beam CT at the three heights from the floor and under three rated parameters (
, μSv/h)$ \bar x \pm s $ 额定参数 距地面0.3 m 距地面0.8 m 距地面1.3 m Z值 P值 Z值 P值 Z值 P值 110 kV/20 mA −2.313a 0.021a −2.524a 0.012a 2.521a 0.012a 90 kV/40 mA −2.521b 0.012b −2.527b 0.012b 2.521b 0.012b 70 kV/60 mA −2.521c 0.012c −2.524c 0.012c 2.524c 0.012c 注:a表示与90 kV/40 mA额定参数比较;b表示与70 kV/60 mA额定参数比较;c表示与110 kV/20 mA额定参数比较 表 2 距地面相同高度处、不同额定参数下距离EVISION-720型移动式头部锥形束CT表面6 m处的周围剂量当量率 的比较
Table 2. Comparison of ambient dose equivalence rates at six meters from the surface of EVISION-720 mobile head cone-beam CT at the same height from the floor and under different rated parameters
距地面高度
(m)70 kV/60 mA 90 kV/40 mA 110 kV/20 mA Z值 P值 Z值 P值 Z值 P值 0.3 −1.192a 0.233a −1.472a 0.141a −0.700a 0.484a 0.8 −0.507b 0.612b −0.169b 0.866b −1.690b 0.091b 1.3 −0.507c 0.612c −1.120c 0.263c −0.420c 0.674c 注:a表示与距地面0.8 m比较;b表示与距地面1.3 m比较;c表示与距地面0.3 m比较 表 3 相同额定参数下、距地面不同高度处距离EVISION-720型移动式头部锥形束CT表面6 m处的周围剂量当量率 的比较
Table 3. Comparison of ambient dose equivalence rates at six meters from the surface of EVISION-720 mobile head cone-beam CT at different heights from the floor and under the same rated parameter
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在110 kV/20 mA额定参数下,以距地面0.3、0.8和1.3 m高度处的3个平面的周围剂量当量率绘制的等剂量曲线(即辐射剂量场分布图)见图1,辐射剂量场呈“对称性”和“三角形”分布。由图1可见:(1)两侧的周围剂量当量率对称,如图中90°与270°方向所示;(2)前方的周围剂量当量率高于两侧和后方,如图中0°与180°方向所示;(3)后方的2个45°方向,即135°和225°方向上的周围剂量当量率最低;(4)正前方,即0°方向上的周围剂量当量率最高,如图中0°方向所示。
EVISION-720型移动式头部锥形束CT辐射剂量场空间分布特点分析
Analysis of spatial distribution characteristics of radiation dose field around EVISION-720 mobile head cone-beam CT
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摘要:
目的 探讨EVISION-720型移动式头部锥形束CT(简称EVISION-720型移动式CT)周围剂量当量率的检测方案并分析其辐射剂量场的空间分布特点。 方法 在0°(EVISION-720型移动式CT正前方)、45°、90°、135°、180°、225°、270°和315°逆时针分布的方向上,选取距地面0.3、0.8和1.3 m高度处的3个平面,以扫描中心为0点位置,分别在距离EVISION-720型移动式CT表面1~10 m处以等间隔1 m的方式布点。采用辐射剂量仪分别在110 kV/20 mA、90 kV/40 mA、70 kV/60 mA的额定参数下,测量距离EVISION-720型移动式CT表面6 m处的检测点位(临床应用时设置的操作位)的周围剂量当量率。在110 kV/20 mA额定参数下,测量所有检测点位的周围剂量当量率。在110 kV/20 mA额定参数下,以距地面0.3、0.8和1.3 m高度处的3个平面的测量结果,绘制1、5、10、20、40、100 μSv/h等剂量曲线,即辐射剂量场分布图。对在不同额定参数下,距地面相同高度处的周围剂量当量率,以及在相同额定参数下,距地面不同高度处的周围剂量当量率分别进行配对Wilcoxon秩和检验。 结果 在3种额定参数下,周围剂量当量率随管电压的增大逐渐增大,不随测量处距地面高度的变化而变化。3种额定参数中,110 kV/20 mA额定参数下0°方向上的周围剂量当量率最大,为(34.44±0.09) μSv/h。在不同额定参数下,距地面相同高度处的周围剂量当量率的差异均有统计学意义(Z=−2.527~2.524,均P<0.05)。在相同额定参数下,距地面不同高度处的周围剂量当量率的差异均无统计学意义(Z=−1.690~−0.169,均P>0.05)。EVISION-720型移动式CT辐射剂量场呈“对称性”和“三角形”分布:后方的2个45°方向,即135°和225°方向上的周围剂量当量率最低;正前方,即0°方向上的周围剂量当量率最高。 结论 EVISION-720型移动式CT辐射剂量场呈左右两侧“对称性”分布和前后“三角形”分布,前方的周围剂量当量率水平高于两侧和后方,医疗机构在使用时应加强对设备前方的辐射防护管理。 -
关键词:
- 辐射剂量 /
- 移动式CT /
- 辐射防护 /
- 体层摄影术,X线计算机
Abstract: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. -
Key words:
- Radiation dosage /
- Mobile CT /
- Radiation protection /
- Tomography, X-ray computed
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表 1 3种额定参数及3种距地面高度处距离EVISION-720型移动式头部锥形束CT表面6 m处的周围剂量当量率(
,μSv/h)$ \bar x \pm s $ Table 1. Ambient dose equivalent rates at six meters from the surface of EVISION-720 mobile head cone-beam CT at the three heights from the floor and under three rated parameters (
, μSv/h)$ \bar x \pm s $ 额定参数 距地面高度(m) 检测点位角度 0° 45° 90° 135° 180° 225° 270° 315° 110 kV/20 mA 0.3 34.44±0.09 12.04±0.37 12.56±0.29 1.23±0.04 9.66±0.11 1.43±0.05 4.70±0.05 9.58±0.03 0.8 28.98±0.05 11.29±0.07 8.69±0.06 1.53±0.03 6.05±0.02 1.54±0.02 9.91±0.06 9.74±0.07 1.3 28.98±0.06 11.40±0.57 12.85±0.04 1.72±0.10 6.55±0.11 1.63±0.05 10.42±0.09 9.26±0.09 90 kV/40 mA 0.3 25.20±0.41 7.93±0.10 8.23±0.07 0.76±0.03 2.01±0.10 0.52±0.05 5.04±0.10 5.46±0.11 0.8 22.60±0.33 7.31±0.12 5.88±0.19 0.73±0.04 2.00±0.16 0.69±0.04 5.63±0.13 4.87±0.17 1.3 21.84±0.42 6.64±0.20 7.81±0.25 0.78±0.05 1.93±0.12 0.69±0.05 5.96±0.19 5.12±0.07 70 kV/60 mA 0.3 9.74±0.20 2.77±0.11 0.92±0.04 0.13±0.02 0.32±0.04 0.19±0.02 0.60±0.04 2.12±0.05 0.8 8.23±0.09 2.69±0.20 0.79±0.07 0.24±0.02 0.35±0.04 0.17±0.02 0.63±0.10 1.80±0.15 1.3 7.81±0.13 2.69±0.20 0.93±0.07 0.18±0.03 0.39±0.05 0.19±0.02 0.71±0.09 1.83±0.10 表 2 距地面相同高度处、不同额定参数下距离EVISION-720型移动式头部锥形束CT表面6 m处的周围剂量当量率 的比较
Table 2. Comparison of ambient dose equivalence rates at six meters from the surface of EVISION-720 mobile head cone-beam CT at the same height from the floor and under different rated parameters
额定参数 距地面0.3 m 距地面0.8 m 距地面1.3 m Z值 P值 Z值 P值 Z值 P值 110 kV/20 mA −2.313a 0.021a −2.524a 0.012a 2.521a 0.012a 90 kV/40 mA −2.521b 0.012b −2.527b 0.012b 2.521b 0.012b 70 kV/60 mA −2.521c 0.012c −2.524c 0.012c 2.524c 0.012c 注:a表示与90 kV/40 mA额定参数比较;b表示与70 kV/60 mA额定参数比较;c表示与110 kV/20 mA额定参数比较 表 3 相同额定参数下、距地面不同高度处距离EVISION-720型移动式头部锥形束CT表面6 m处的周围剂量当量率 的比较
Table 3. Comparison of ambient dose equivalence rates at six meters from the surface of EVISION-720 mobile head cone-beam CT at different heights from the floor and under the same rated parameter
距地面高度
(m)70 kV/60 mA 90 kV/40 mA 110 kV/20 mA Z值 P值 Z值 P值 Z值 P值 0.3 −1.192a 0.233a −1.472a 0.141a −0.700a 0.484a 0.8 −0.507b 0.612b −0.169b 0.866b −1.690b 0.091b 1.3 −0.507c 0.612c −1.120c 0.263c −0.420c 0.674c 注:a表示与距地面0.8 m比较;b表示与距地面1.3 m比较;c表示与距地面0.3 m比较 -
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