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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One of the challenging applications of PET is implementing it for in-beam PET, which is an in situ monitoring method for charged particle therapy. For this purpose, we have previously proposed an open-type PET scanner, OpenPET. The original OpenPET had a physically opened field of view (FOV) between two detector rings through which irradiation beams pass. This dual-ring OpenPET (DROP) had a wide axial FOV including the gap. This geometry was not necessarily the most efficient for application to in-beam PET in which only a limited FOV around the irradiation field is required. Therefore, we have proposed a new single-ring OpenPET (SROP) geometry which can provide an accessible and observable open space with higher sensitivity and a reduced number of detectors than the DROP. The proposed geometry was a cylinder shape with its ends cut at a slant, in which the shape of each cut end became an ellipse. In this work, we developed and evaluated a small prototype of the SROP geometry for proof-of-concept. The SROP prototype was designed with 2 ellipse-shaped detector rings of 16 DOI detectors. The DOI detectors consisted of 1024 GSOZ crystals which were arranged in 4 layers of 16 X 16 arrays, coupled to a 64-ch FP-PMT. Each ellipse-shaped detector ring had a major axis of 281.6 mm and a minor axis of 207.5 mm. For the open mode, the rings were placed at a 45-deg slant from the axial direction and for the non-open mode (used as a reference) they were at 90 deg from the axial direction with no gap. The system sensitivity and average spatial resolution were measured from a 22Na point source and were 5.0 % and 2.7 mm, respectively, for the open mode. Comparison between the open mode and the non-open mode showed no remarkable difference in terms of the sensitivity distribution and spatial resolution performance. Therefore, we concluded that the SROP geometry has a good potential as an open geometry especially suitable for in-beam imaging.
Development and performance evaluation of a single-ring OpenPET prototype
