@article{oai:repo.qst.go.jp:00047121,
 author = {Hirano, Yoshiyuki and Yoshida, Eiji and Kinouchi, Shoko and Nishikido, Fumihiko and Inadama, Naoko and Murayama, Hideo and Yamaya, Taiga and 平野 祥之 and 吉田 英治 and 木内 尚子 and 錦戸 文彦 and 稲玉 直子 and 村山 秀雄 and 山谷 泰賀},
 issue = {7},
 journal = {Physics in medicine and biology},
 month = {Mar},
 note = {In-beam positron emission tomography (PET) can enable visualization of an irradiated field using positron emitters (β+ decay). In particle therapies, many
kinds of secondary particles are produced by nuclear interactions, which affect
PET imaging. Our purpose in this work was to evaluate effects of secondary
particles on in-beam PET imaging using the Monte Carlo simulation code, Geant4, by reproducing an experiment with a small OpenPET prototype in which a PMMA phantom was irradiated by a 11C beam. The number of incident particles to the detectors and their spectra, background coincidence for the PET scan, and reconstructed images were evaluated for three periods, spill-time (beam irradiation), pause-time (accelerating the particles) and beamoff time (duration after the final spill). For spill-time, we tested a background reduction technique in which coincidence events correlated with the accelerator radiofrequency were discarded (RF gated) that has been proposed in the literature. Also, background generation processes were identified. For spilltime,
most background coincidences were caused by prompt gamma rays, and only 1.4% of the total coincidences generated β+ signals. Differently, for pause-time and beam-off time, more than 75% of the total coincidence events were signals. Using these coincidence events, we failed to reconstruct images during the spill-time, but we obtained successful reconstructions for the pausetime and beam-off time, which was consistent with the experimental results. From the simulation, we found that the absence of materials in the beam line and using the RF gated technique improved the signal-to-noise ratio for the spill-time. From an additional simulation with range shifter-less irradiation and the RF gated technique, we showed the feasibility of image reconstruction during the spill-time.},
 pages = {1623--1640},
 title = {Monte Carlo simulation of small OpenPET prototype with 11C beam irradiation: effects of secondary particles on in-beam imaging},
 volume = {59},
 year = {2014}
}