Study on Detectors for On-line Measurement and estimation of absorbed energy using SPECT system in Neutron Capture Therapy

本研究的目的是阐明具有快速伽马分析的单光子发射计算机断层扫描系统（称为PG-SPECT系统）的可行性，该系统有望成为一种有效的活体剂量分布实时测量方法。重点介绍了探测器材料及其尺寸的优化，以及在系统维护方面的改进，如停止使用液氮冷却等，这是半导体探测器通常不可缺少的。1995年（Heisei 7）研究了Ge半导体探测器和CdTe半导体探测器在PG-SPECT系统中的适用性。特别是，碲化镉探测器被认为是一个足够的探测器，因为它的可能性缩小和不使用冷却的最近显著的创新。1996年（Heisei 8）估计了CdTe探测器在室温下的特性，并通过实验和模拟计算研究了应用Peltier效应的简单冷却方法的有效性。证实了采用珀尔帖冷却的碲化镉探测器具有很大的发展潜力。此外，还利用1995年购入的聚乙烯和6liff以30%的重量混合制成了热中子屏蔽片，并通过实验证实了其有效性。1997年（Heisei 9）继续通过实验和模拟计算对Ge探测器和CdTe探测器的特性进行评价。此外，还研究了(1)在低计数下统计误差的减小和(2)在中子和伽马射线混合场下小尺寸探测器的准直系统。从这些结果中，一些新的研究对象被提取出来用于下一步。

The purpose of this research is to clarify the feasibility of single photon emission computed tomography system with prompt gamma analysis (named PG-SPECT system), which is expected as an effective real-time measurement method for dose distribution in a living body. We put emphasis on the optimization of the detector material and its size, and the improvement in the system maintenance, such as disuse of the cooling with liquid nitrogen etc., which is usually indispensable to semiconductor detector.In 1995 (Heisei 7), the applicability of Ge semiconductor detector and CdTe semiconductor detector to the PG-SPECT system were studied. Especially, the CdTe detector is thought to be an adequate detector for this system, because of its possibilities of downsizing and disuse of the cooling by the recent remarkable innovation.In 1996 (Heisei 8), the characteristics of CdTe detector at room temperature was estimated, and the effectiveness of the simple cooling method applying Peltier effect was researched by experiments and simulation calculation. It was confirmed that the CdTe detector with the Peltier cooling had great potentialities. Moreover, shielding sheets for thermal neutrons were made using polyethylene mixed with 6LiF,which purchased in 1995, at 30 weight percent, and its effectiveness was confirmed from experiments.In 1997 (Heisei 9), the characteristics evaluation of Ge detector and CdTe detector was continued by experiments and simulation calculations. Furthermore, (1) the reduction of statistical error at low-counts and (2) the collimation system for small-size detector at mixed field of neutrons and gamma-rays were examined. From those results, some research subjects are newly extracted for the next steps.