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

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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.