Department of Medical Physics, Rush University Medical Center, Chicago, Illinois, 60612.
J Appl Clin Med Phys. 2009 Oct 15;10(4):142-150. doi: 10.1120/jacmp.v10i4.2911.
A method to evaluate the electron beam energy constancy by employing the computed radiography (CR) system has been developed. In this method, a right triangular plastic wedge is used to produce a curve of the CR storage phosphor plate signal versus the wedge thickness. The curve, which resembles the percentage depth ionization curve of the clinical electron beams, can be used to derive the energy constancy metric EC(50). The sensitivity of the method was tested using polystyrene sheets of variable thicknesses. For electron energies up to 12 MeV, energy changes induced by 1.5 mm thick polystyrene can be detected, while a 2.3 mm thick polystyrene sheet is required for higher energies. The measurements were carried out over a two-year period. The results showed a good reproducibility with the use of the same CR plate and cassette, and without the requirement of calibration procedures. The two-year range of the EC(50) was within the 99% confidence intervals, and the standard deviation of the EC(50) was measured to be from 0.3 to 0.4 mm for different beam energies. This technique provides an efficient and accurate method to perform the electron beam energy check and could be used by centers equipped with the CR system without requiring additional detection devices.
一种利用计算机射线照相（CR）系统评估电子束能量稳定性的方法已经开发出来。在该方法中，使用直角塑料楔块产生 CR 存储磷光体板信号与楔块厚度的曲线。该曲线类似于临床电子束的百分深度电离曲线，可用于导出能量稳定性指标 EC(50)。该方法的灵敏度使用不同厚度的聚苯乙烯片进行了测试。对于能量高达 12 MeV 的电子，可检测到 1.5 毫米厚聚苯乙烯引起的能量变化，而对于更高的能量，则需要 2.3 毫米厚的聚苯乙烯片。测量在两年期间进行。结果表明，使用相同的 CR 板和盒，并且不需要校准程序，具有良好的可重复性。EC(50) 的两年范围在 99%置信区间内，并且对于不同的束能，EC(50)的标准偏差测量值为 0.3 至 0.4 毫米。该技术提供了一种高效准确的电子束能量检查方法，配备 CR 系统的中心无需额外的检测设备即可使用。
