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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1) Introduction
We are developing the OpenPET, which can provide an open space observable and accessible to the patient during PET measurements. One of the applications for the OpenPET is real-time tumor tracking which can realize real-time PET-guided radiation therapy. We have developed real-time imaging system for the OpenPET and implemented it on the small OpenPET prototype. The developed system demonstrated ability to track a moving point source positioned in the open space. In actual situations, however, radioactivity concentrates not only tumor but also surrounding organs and it is uncertain whether the tumor tracking is feasible in human body. In this study, we conducted a Monte Carlo simulation to investigate the conditions under which the tumor tracking by human-sized OpenPET is feasible.
2) Method
For a realistic simulation, we used the 4D extended cardiac-torso (XCAT) phantom, which is a realistic 4D human whole body phantom, and assigned 18F-FDG standardized uptake values (SUVs) to normal organs based on the literature. As a Monte Carlo simulation toolkit, we used geant4 application for tomographic emission (GATE) ver. 6.1. A sphere-shaped tumor was placed on upper left lung. List-mode data were generated for each 0.5 s time frame of a respiratory cycle of 5 s with various tumor sizes and SUVs. 4D images were reconstructed in a frame-by-frame manner and tumor position was automatically extracted for each time frame by a pattern matching technique.
3) Result
The mean error of the tumor positions extracted from the reconstructed images with time frames of 0.5 s was similar to the PET image resolution when the tumor had radioactivity concentration above certain amount.
4) Conclusion
We showed that tumor tracking by the OpenPET is feasible even in the human body scale and for realistic conditions.
Feasibility study of real-time tumor tracking by OpenPET during radiotherapy
