量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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We are developing the OpenPET which can provide an open space observable and accessible to the patient during PET measurements. In addition, we have proposed the real-time imaging system for the OpenPET which is expected to be used in PET-guided tumor tracking radiation therapy and demonstrated its tracking ability using a point source and a small OpenPET prototype. However, tumor tracking in the human body still remains as a challenging task when we use 18F-FDG which is the best available tracer for tumors because of its background activity, scatter and attenuation in the body. In this study, we assess conditions under which tumor tracking is feasible in the human body by using the 4D XCAT phantom which is a realistic 4D human whole body phantom. To simulate realistic 18F-FDG distributions, we assigned standardized uptake values (SUVs) to normal organs based on the literature. At this stage, we generated simulated projection data by forward projection of each time frame incorporating detector response functions of the human-sized OpenPET geometry. The number of events in the projection data in the time frame of 0.5 s was adjusted to 500 k counts assuming the 18F-FDG injection of 370 MBq and a spherical tumor with the diameter of 10 mm and SUV of 5, and taking the system sensitivity into account. Then Poisson noise was added. Image reconstruction was done in a frame-by-frame manner and tumor position was automatically extracted for each time frame by a pattern matching technique. Tumor movement in the 4D XCAT phantom was about 17 mm at the maximum. The mean error of the tumor positions extracted from the reconstructed images was about 2.7 mm, which is equivalent to the PET image resolution. We showed that tumor tracking by the OpenPET is feasible even in the human body scale and for realistic conditions. By the time of the conference, we will have conducted a Monte Carlo simulation with the human-sized OpenPET and assessed conditions under which the tumor tracking is feasible.
会議概要（会議名, 開催地, 会期, 主催者等）
2012 Nuclear Science Symposium, Medical Imaging Conference & Workshop on Room-Temperature Semiconductor X-Ray and Gamma-Ray Detectors
Simulation study of real-time tumor tracking by OpenPET using the 4D XCAT phantom with a realistic 18F-FDG distribution
