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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Objectives: We are developing the OpenPET which can provide an accessible open space to the patient during PET scanning. In addition, we have proposed the real-time imaging system for the OpenPET toward PET-guided tumor-tracking radiation therapy. Although we demonstrated its tracking ability using a point source and a small OpenPET prototype, tumor tracking in human body is still challenging task because of its background activity when we use the 18F-FDG which is the best available tracer for tumors. In this study, we access conditions that the tumor tracking is feasible in human body by using the 4D XCAT phantom which is a realistic 4D human whole body phantom.
Methods: For generating 4D XCAT phantom with appropriate 18F-FDG distribution, SUVs were assigned to normal organs from literature. Spherical lesion with the SUV of 5 was placed at the right upper lung moving with respiratory cycle of 5 s. 4D Image was generated with the frame rate of 2 fps. Then, projection data of each frame were generated by forward projection with the system matrix including detector response functions of the human-sized OpenPET geometry having a gap of 300 mm. Detector blocks were 16x16x4 arrays of 3.0x3.0x7.5 mm3 scintillators. Attenuation of the body was included in the simulation, but scattering was ignored. Assuming the 18F-FDG injection of 370 MBq and time frame of 0.5 s and taking the system sensitivity into account, total event count in each projection data was adjusted to 500 k counts and then Poisson noise was added. 4D image was reconstructed frame by frame using the 3D OSEM method. Tumor position was extracted from the reconstructed 4D image by a pattern matching method.
Results: Tumor was moved 17 mm at the maximum with respiratory motion. Average error of the tumor position extracted from the reconstructed image was 2.7 mm, which was similar to the PET resolution.
Conclusions: We showed that tumor tracking by the OpenPET is feasible even in a realistic case.
Research Support: This work was partially supported by the Grant-in-Aid for Scientists Research (A) of Kakenhi (22240065) and by a research grant from the Association for Nuclear Technology in Medicine.
Simulation study of real-time tumor tracking by the OpenPET using 4D XCAT phantom with 18F-FDG distribution
