New methods of radiation dosimetry in medicine by using optical fibers

本研究的目的是利用光纤作为X射线剂量计的探测材料，发展新型的辐射剂量计和医学辐射剂量测量的新方法。研究的重点是以下三个发展。1.设计了一个长的剂量计的数量级为一米，通过使用一个塑料光纤作为探测器材料，测量剂量积分的X射线CT曝光在人体模型上沿着平行于X射线源的旋转轴的线。通过处理来自光纤两端的光信号，在约一米的范围内获得了均匀的剂量计灵敏度。使用长剂量计测量的CT剂量表明，使用探测长度较短的常规CT室所获得的饱和剂量积分被低估.设计了一种用于小野治疗X射线剂量精确测量的小型组织等效探测器。利用单位增益光电二极管将探测器输出的光转换为电信号，而不需要光电倍增管，提出了一种新的由脉冲高度谱估算吸收剂量的方法，获得了信噪比高、重现性好的剂量值.利用塑料闪烁光纤芯片和一对光纤光导，设计了一种用于CT照射剂量测量的小型、高灵敏度、响应方向无关的X射线探测器。测量人体胸部体模中沿着平行于X射线源旋转轴的线的剂量分布和体模中不同位置的点剂量，用于螺旋CT检查，以估计组织或器官剂量。

The purpose of the present study is the development of novel radiation dosimeters and new methods of radiation dosimetry in medicine by using optical fiber as detector material of x-ray dosimeters. The study was focused on the following three developments.1. A long dosimeter on the order of one meter was devised by using a plastic scintillating fiber as detector material for measuring dose integral by x-ray CT exposure on a human phantom along lines parallel to the axis of rotation of the x-ray source. Uniform sensitivity of the dosimeter was attained over a range of about one meter by processing light signals derived from both ends of the fiber. Measurements of CT doses with the long dosimeter indicated the underestimation of saturated dose integral that had been obtained with conventional CT chambers with a short detection length.2. A small sized and tissue equivalent detector consisting of a plastic scintillating fiber chip coupled with an optical fiber light guide was devised for the precise dosimetry of small field therapeutic x-ray beams. Light output from the detector was converted to electrical signal with unity gain photodiodes without using photomultipliers, and a novel method to estimate absorbed dose from pulse height spectra was developed to obtain dose values with a large signal-to-noise ratio and excellent reproducibility.3. A small sized and highly sensitive x-ray detector with directional independence of response was devised for the dosimetry of CT exposure by using a plastic scintillation fiber chip and a pair of optical fiber light guides. Dose profiles in a human chest phantom along lines parallel to the axis of rotation of the x-ray source and point doses at various positions in the phantom were measured for helical CT examinations to estimate tissue or organ doses.