Waggener R G, Blough M M, Terry J A, Chen D, Lee N E, Zhang S, McDavid W D
Radiology Department, University of Texas Health Science Center at San Antonio, 78284-7800, USA.
Med Phys. 1999 Jul;26(7):1269-78. doi: 10.1118/1.598622.
Attenuation measurements for primary x-ray spectra from 25 kVp to 18 MV were made using aluminum filters for all energies except for orthovoltage where copper filters were used. An iterative perturbation method, which utilized these measurements, was employed to derive the apparent x-ray spectrum. An initial spectrum or pre-spectrum was used to start the process. Each energy value of the pre-spectrum was perturbed positively and negatively, and an attenuation curve was calculated using the perturbed values. The value of x-rays in the given energy bin was chosen to minimize the difference between the measured and calculated transmission curves. The goal was to derive the minimum difference between the measured transmission curve and the calculated transmission curve using the derived x-ray spectrum. The method was found to yield useful information concerning the lower photon energy and the actual operating potential versus the nominal potential. Mammographic, diagnostic, orthovoltage, and megavoltage x-ray spectra up to 18 MV nominal were derived using this method. The method was validated using attenuation curves from published literature. The method was also validated using attenuation curves calculated from published spectra. The attenuation curves were then used to derive the x-ray spectra.
除了在正交电压（使用铜滤过器）的情况下，对于25 kVp至18 MV的一次X射线光谱，使用铝滤过器进行了衰减测量。采用一种利用这些测量值的迭代微扰法来推导表观X射线光谱。使用初始光谱或预光谱来启动该过程。预光谱的每个能量值进行正向和负向微扰，并使用微扰值计算衰减曲线。选择给定能量区间内X射线的值，以使测量的和计算的透射曲线之间的差异最小化。目标是使用推导的X射线光谱，使测量的透射曲线与计算的透射曲线之间的差异最小。发现该方法可得出有关较低光子能量以及实际工作电位与标称电位的有用信息。使用该方法推导了高达18 MV标称值的乳腺摄影、诊断、正交电压和兆伏级X射线光谱。使用已发表文献中的衰减曲线对该方法进行了验证。还使用从已发表光谱计算出的衰减曲线对该方法进行了验证。然后使用衰减曲线来推导X射线光谱。
