@misc{oai:repo.qst.go.jp:00064876,
 author = {Yamaya, Taiga and Yoshida, Eiji and Kinouchi, Shoko and Nakajima, Yasunori and Nishikido, Fumihiko and Hirano, Yoshiyuki and Tashima, Hideaki and Ito, Hiroshi and Haneishi, Hideaki and Satou, Shinji and Inaniwa, Taku and 山谷 泰賀 and 吉田 英治 and 木内 尚子 and 中島 靖紀 and 錦戸 文彦 and 平野 祥之 and 田島 英朗 and 伊藤 浩 and 羽石 秀昭 and 佐藤 眞二 and 稲庭 拓},
 month = {Dec},
 note = {Introduction: An open-type PET geometry, "OpenPET" is our original idea to visualize a physi-cally opened space even with a full ring geometry. One of our targets is in-beam PET, which is a method for in situ monitoring of charged particle therapy [1]. We aim to develop the first practical 3D geometry realized, as conventional systems using positron cameras are basically limited to 2D imaging with low sensitivity [2-4]. In our initial idea, the OpenPET had a physically opened field-of-view (FOV) between two detector rings separated by a gap (Figure 1 (a)) [5][6]. Originally, the OpenPET was proposed to provide a stress-less brain imaging device. For a dedicated in-beam PET scanner, this dual-ring OpenPET is a good candidate, but it is not nec-essarily the most efficient geometry because it has a wide FOV (i.e., a gap FOV plus two in-ring FOVs) while only a limited FOV around the irradiation field is required in actual use of in-beam PET. In the last year, therefore, we proposed a single-ring OpenPET (SROP) dedicated for in-beam PET as our 2nd gen-eration geometry [7]. In this paper, we developed a small prototype of the SROP for a proof-of-concept. 
\nMaterials and methods: The detector ring of the SROP geometry is the cylinder both ends of which are cut by parallel aslant planes (Figure 1 (b)). The geometry has a gap through which a treatment beam passes. A similar gap can be made simply by slanting a conventional PET scanner as indicated in [8]. Compared with this conventional idea, the proposed geometry has an advantage of compactness so that the beam port can be placed closer to the patient. In addition, the compactness enables efficient design with respect to the sensitivity and the cost (i.e., the number of detectors) [9]. 
The small SROP prototype consisted of 2 ellipse-shaped detector rings, each of which had 16 detectors. Each ellipse-shaped detector ring had a major axis of 281.6 mm and a minor axis of 207.5 mm. The rings were slanted by 45 deg and staggered to obtain an open space of 74.5 mm width. We carried out initial in-beam phantom imaging tests in the Heavy Ion Medical Accelerator in Chiba (HIMAC) using a 11C beam as well as a 12C beam. PET measurement started at the beginning of the irradiation, and continued for 20 min after the irra-diation. 
\nResults: For about 3Gy irradiation, a 6 mm range difference was clearly detected with the 11C beam irradiation. Compared with the 12C beam irradiation, PET images directly corresponding to the distribution of primary particles were obtained in the radioactive beam irradiation. 
\nConclusions: Our initial imaging studies showed promising performance of the SROP prototype., Micro- Mini- and Nano- Dosimetry（MMND2012）　&　International Prostate Cancer Treatment (IPCT2012) International Workshop},
 title = {DEVELOPMENT OF A NOVEL OPEN-TYPE PET SYSTEM FOR 3D DOSE VERIFICATION IN CARBON ION THERAPY},
 year = {2012}
}