目的:开发一种进行X射线管质量控制(QC)和自动曝光控制(AEC)的方法,作为射线照相和荧光透视X射线系统QC的一部分。我们的目的是通过比较测得的辐射输出来验证X射线管的输出,或者空气克尔,给定应用的曝光设置和几何形状的理论输出,除了将测量的kV与标称kV进行比较。通过确定对具有不同厚度的均质体模的吸收剂量来评估用于荧光透视和常规X射线系统的AEC系统。
方法:本研究提出了一种验证X射线管测量结果的模型,以及一种确定对同质体模(Dphantom)的剂量的方法。需要以下输入:X射线光谱的参数化模型,使用多功能X射线计测量X射线管,通过使用AEC模拟患者的不同厚度的聚甲基丙烯酸甲酯(PMMA)平板成像记录的曝光参数,和一个参数化模型,用于从蒙特卡罗模拟中计算水的剂量。输出是体模中的入射表面剂量(ESD)和吸收剂量,幻影(µGy)。此外,参数化X射线光谱用于比较理论和测量的空气角力,作为X射线管QC的一部分。为了验证所提出的方法,这项研究提供的X射线光谱,光谱,与两个市售光谱进行了比较,SpekCalc和医学物理与工程研究所(IPEM)78。将赋予均匀体模的能量分数与通过PCXMC计算的赋予分数进行比较。
结果:本研究中提供的光谱与先前发表的两个X射线光谱非常吻合。光谱的绝对百分比差异从0.05%到3.9%不等,平均为1.4%,与SpekCalc相比。同样,与IPEM报告78的偏差从0.02%到2.3%不等,平均为0.74%。对SPECTRUM进行参数化,以计算10°目标角度的赋予分数,12°,15°,kV(50-150kV)与材料Al(2.2-8mm),Cu(0-1mm),以及过滤器的任何组合,PMMA和水。对于不同kV的所有测量,PCXMC与结果的能量偏差小于8%,过滤,和供应商,通过使用PMMA记录曝光参数获得,而剂量是基于与PMMA相同厚度的水计算的。
结论:本研究提供了一种准确且合适的方法,可以相对于X射线管和相关的AEC系统执行荧光透视和常规X射线系统的部分QC。该方法适用于通过吸收剂量比较系统内和系统之间的方案。
OBJECTIVE: To develop a method to perform quality control (QC) of X-ray tubes and automatic exposure control (AEC) as a part of the QC of the radiographic and fluoroscopic X-ray system. Our aim is to verify the output from the X-ray tube by comparing the measured radiation output, or air kerma, to the theoretical output given the applied exposure settings and geometry, in addition to comparing the measured kV to the nominal kV. The AEC system for fluoroscopic and conventional X-ray systems is assessed by determining the absorbed dose to a homogenous phantom with different thicknesses.
METHODS: This study presents a model to verify the X-ray tube measurement results and a method to determine the dose to a homogenous phantom (Dphantom ). The following input is needed: a parameterized model of the X-ray spectrum, the X-ray tube measurements using a multifunctional X-ray meter, the exposure parameters recorded via imaging of polymethyl methacrylate (PMMA) slabs of different thickness that simulate the patient using AEC, and a parameterized model for calculating the dose to water from Monte Carlo simulations. The output is the entrance surface dose (ESD) and absorbed dose in the phantom, Dphantom (µGy). In addition, the parameterized X-ray spectrum is used to compare theoretical and measured air kerma as a part of the QC of the X-ray tube. To verify the proposed method, the X-ray spectrum provided in this study, SPECTRUM, was compared to two commercially available spectra, SpekCalc and Institute of Physics and Engineering in Medicine (IPEM) 78. The fraction of energy imparted to the homogenous phantom was compared to the imparted fraction calculated by PCXMC.
RESULTS: The spectrum provided in this study was in good agreement with two previously published X-ray spectra. The absolute percentage differences of the spectra varied from 0.05% to 3.9%, with an average of 1.4%, compared to SpekCalc. Similarly, the deviation from IPEM report 78 varied from 0.02% to 2.3%, with an average of 0.74%. The SPECTRUM was parameterized for calculation of the imparted fraction for target angles of 10°, 12°, and 15°, kV (50-150 kV) with the materials Al (2.2-8 mm), Cu (0-1 mm), and any combination of the filters, PMMA and water. The deviation of energy imparted from the results by PCXMC was less than 8% for all measurements across different kV, filtration, and vendors, obtained by using PMMA to record the exposure parameters, while the dose was calculated based on water with same thicknesses as the PMMA.
CONCLUSIONS: This study presents an accurate and suitable method to perform a part of the QC of fluoroscopic and conventional X-ray systems with respect to the X-ray tube and the associated AEC system. The method is suitable for comparing protocols within and between systems via the absorbed dose.