Development of new devices measuring dose distributions in a tissue equivalent material and incident electron energies for therapeutic electron beams

1. 研制了一种新型的电子束能量监测仪，用于检测放射治疗加速器的电子束能量。监视器由一对闪烁光纤和光电二极管读出电路组成，测量电子通过楔形吸收器传输的能量依赖性。该监测仪具有线性能量响应和1%的能量常数测量精度。该监视器具有机电结构简单、体积小、成本低等优点，适合作为便携式设备实际应用。研制了一种用于电子束治疗的新型深度剂量测量装置。该装置采用塑料闪烁光纤探测器，沿入射电子束插入塑料（PMMA）模体。从光纤输出的光子，其数量与在幻影的每个深度的吸收剂量成正比，被光电二极管转换成电信号。来自光电二极管的每个信号通过多通道AD转换器传输到个人计算机，并进行处理，在计算机显示器上绘制深度-剂量曲线。在5秒的测量时间内，可以得到每个入射电子束的深度-剂量曲线，其能量范围在4 - 21 MeV之间。使用曲线和PMMA的深度缩放因子估计的平均电子能量与使用离子室和水模体的传统深度剂量测量结果一致。新开发的装置，简单，不耗时，适合常规使用作为治疗电子束的质量保证工具。

1. A new type of beam-energy monitor has been developed to check the energies of electron beams from radiotherapy accelerators. The monitor consists of a pair of scintillating fibers and photodiode read-out circuits that measure the energy depencence of electron transmission through a wedge-shaped absorber. A linear energy response and 1% accuracy for energy constancy measurements were attained with the monitor. The monitor having advantages of simple mechanical and electronic constructions, small size and low cost is suitable for practical use as a portable device.2. A new type of depth-dose measuring device has been developed for electron beam therapy. The device employs plastic scintillating fiber detectors inserted in a plastic (PMMA) phantom in line along an incident electron beam. Output photons from a fiber, the number of which is proportional to absorbed dose at each depth of the phantom, were converted to an electric signal with a photodiode. Each signal from the photodiode was transmitted to a personal computer through a multi-channel AD converter and processed to draw a depth-dose curve on the computer display. A depth-dose curve could be obtained in a measuring time of 5 sec for each incident electron beam with an energy range between 4 and 21 MeV.The mean electron energies estimated using the curves and a depth-scaling factor for PMMA were consistent with those obtained by conventional depth-dose measurements using an ion chamber and a water phantom. The newly developed device, being simple and not time consuming, is suitable for routine use as a quality assurance tool for therapeutic electron beams.