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(简称PG-SPECT系统)的可行性，该系统有望成为一种有效的实时测量活体内剂量分布的方法。我们着重于探测器材料和尺寸的优化，以及系统维护的改进，如取消半导体探测器常用的液氮冷却等。1995年(平成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，由于最近显著的创新，镉镉探测器被认为是一种适合于该系统的探测器，因为它具有小型化和不再使用冷却的可能性。1996年(平成8)对镉镉探测器的室温特性进行了评估，并通过实验和模拟计算研究了利用帕尔蒂埃效应的简单冷却方法的有效性。证实了Peltier冷却的CdTe探测器具有很大的潜力。此外，用1995年购买的聚乙烯与6LiF混合，以30%的重量百分比制作了热中子屏蔽片，并从实验中证实了其有效性。1997年，通过实验和模拟计算，继续对Ge探测器和CdTe探测器的特性进行了评估。此外，还研究了(1)低计数统计误差的减小和(2)小尺寸探测器在中子和伽马射线混合场的准直系统。从这些结果中，为下一步的研究提取了一些新的研究对象。

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.