Development of a organ dose measuring system to investigate exposure dose to pediatric patient by diagnostic x rays

本研究的目的是设计一种方便的剂量测定系统，用于测量接受临床x射线检查的儿科患者的器官剂量，特别是高暴露剂量的CT扫描，并调查诊断性x射线医疗暴露给儿科患者的剂量水平。剂量测量系统采用新开发的光电二极管剂量计，安装在一个拟人模型中，实现了体重20公斤，身高115厘米的标准6岁日本儿童。球形硅光电二极管剂量计，32个，被植入到组织或器官的位置，在ICRP的定义有效剂量内的幻影。设计了电子电路，将每个剂量计中产生的电流信号转换成与暴露在x射线下沉积的剂量成比例的信号。同时开发了一种计算机程序，通过模数转换器将剂量计信号读入个人计算机，并将信号转换为软组织吸收剂量，用标准离子室剂量计校准，计算出器官和有效剂量。在小儿常规胸部、腹部和头部CT检查中，采用新型器官剂量测量系统，使用德国西门子、日本东芝等典型厂家最新或最新型号的多层螺旋CT扫描仪进行暴露剂量测量。使用我们的新系统，我们可以获得大量的数据来解释目前儿科患者在x射线CT检查中的剂量水平。所获得的数据表明了最近的CT扫描仪采用的减剂量技术的有效性，并阐明了这些CT扫描仪采用的管电流调制机制来减少器官剂量。

The objective of this study was to devise a convenient dosimetry system for measuring organ doses of pediatric patients undergoing clinical x-ray examinations and particularly CT scans delivering high exposure doses, and to investigate the level of doses deposited to pediatric patients by medical exposure from diagnostic x-rays.1. The dosimetry system was constructed using newly developed photodiode dosimeters installed in an anthropomorphic phantom realizing standard six-year-old Japanese children, 20 kg in weight and 115 cm tall. Spherical silicon photodiode dosimeters, 32 in number, were implanted at the positions of the tissues or the organs assigned in the ICRP's definition of the effective dose within the phantom. Electronic circuits were devised, which converted current signal generated in each dosimeter to the signal proportional to the dose deposited through exposure to x-rays. Also developed was a computer program which could read out dosimeter signals to a personal computer through analog-to-digital converters and convert the signals to absorbed doses for soft tissue calibrated by using standard ion chamber dosimeter to calculate organ and the effective doses.2. Exposure dose measurements were carried out using the new organ dose measuring system in routine pediatric chest, abdomen and head CT examinations by using multislice helical CT scanners of recent or the latest models from typical manufacturers as Siemens (Germany) and Toshiba (Japan). Using our new system we could obtain a large amount of data to explicate the present dose levels for pediatric patients in x-ray CT examinations. The data obtained indicated the effectiveness of dose reducing technique adopted by the recent CT scanners and clarified the reduction of organ doses by the use of tube current modulation mechanism adopted by these CT scanners.