@misc{oai:repo.qst.go.jp:00063916,
 author = {Yamaya, Taiga and Yoshida, Eiji and Nishikido, Fumihiko and Inadama, Naoko and Inaniwa, Taku and Satou, Shinji and Yoshikawa, Kyosan and Kinouchi, Shoko and Suga, Mikio and Tsuji, Atsushi and Murayama, Hideo and 山谷 泰賀 and 吉田 英治 and 錦戸 文彦 and 稲玉 直子 and 稲庭 拓 and 佐藤 眞二 and 吉川 京燦 and 木内 尚子 and 菅 幹生 and 辻 厚至 and 村山 秀雄},
 month = {May},
 note = {1. Propose
The OpenPET geometry, which visualizes a physically opened space between two detector rings, is our new idea to enable PET imaging during radiation therapy. In particular, OpenPET is expected to realize in-beam 3D PET, which is a method for an in situ monitoring of charged particle therapy, by letting the beams pass through the gap. Tracking a moving target such as a tumor in the lung will also become possible if the real-time image reconstruction becomes available. In addition, real-time monitoring of therapeutic gain might be possible in the future when a new PET tracer that quickly responds to radiotherapy is developed. In this paper, we developed the first prototype of the OpenPET for a proof-of-concept, and we carried out the first in-beam tests in the Heavy Ion Medical Accelerator in Chiba (HIMAC). 
2. Methods
The prototype was designed as a compact system so as to be easily carried between PET areas and the HIMAC. Two detector rings of 110 mm in diameter composed of 8 block-detectors were placed with a variable gap from 15 mm to 44 mm. Actual maximum gap was limited to 27mm by the gantry structure. Each block-detector, which had 4-layer depth-of-interaction capability, was composed of 2.9 x 2.9 x 5.0 mm3 LGSO crystals and a Hamamatsu H8500 PMT. In order to reduce radiation damage to electronic circuits caused by secondary particles such as neutron, front-end circuits and detector heads were separated and connected by coaxial cables of 1.2 m long. 
The prototype system was positioned so that the beam passes through the gap between two detector rings. A PMMA cylindrical phantom of 4cm in diameter, placed in the center of the PET field-of-view, was irradiated along radial direction by a 11C pencil beam. The beam diameter was 15mm, the range in the phantom was about 20mm, and the irradiation rate was 106 particles per sec in order. At this development stage, dynamic data acquisition to extract useful data among the beam-cycle of 3.3 sec was not ready in our measurement system. PET measurement (20 min) started just after 20 min irradiation.
3. Results
PET images corresponding to dose distribution were obtained. Compared to the similar "off-beam" experiments, the same images were obtained.
4. Conclusions
We developed a small OpenPET prototype and the first in-beam studies showed promising performance of the OpenPET., PTCOG49},
 title = {First in-beam tests of a small OpenPET prototype for a proof-of-concept of PET imaging during particle therapy},
 year = {2010}
}