Monitoring of positron using high-energy gamma camera for proton therapy
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ORIGINAL ARTICLE
Monitoring of positron using high-energy gamma camera for proton therapy Seiichi Yamamoto • Toshiyuki Toshito • Masataka Komori • Yuki Morishita • Satoshi Okumura • Mitsutaka Yamaguchi • Yuichi Saito • Naoki Kawachi • Shu Fujimaki
Received: 30 July 2014 / Accepted: 25 November 2014 Ó The Japanese Society of Nuclear Medicine 2014
Abstract Purpose In proton therapy, imaging of proton-induced positrons is a useful method to monitor the proton beam distribution after therapy. Usually, a positron emission tomography (PET) system installed in or near the proton beam treatment room is used for this purpose. However, a PET system is sometimes too large and expensive for this purpose. We developed a small field-of-view (FOV) gamma camera for high-energy gamma photons and used it for monitoring the proton-induced positron distribution. Methods The gamma camera used 0.85 mm 9 0.85 mm 9 10 mm Ce:Gd3Al2Ga3O12 (GAGG) pixels arranged in 20 9 20 matrix to form a scintillator block, which was optically coupled to a 1-inch-square position-sensitive photomultiplier tube (PSPMT). The GAGG detector was encased in a 20-mm thick container and a pinhole collimator was mounted on its front. The gamma camera was set 1.2 m from the 35 cm 9 35 cm 9 5 cm plastic phan-
tom in the proton therapy treatment room, and proton beams were irradiated to the phantom with two proton energies. Results The gamma camera had spatial resolution of *6.7 cm and sensitivity of 3.2 9 10-7 at 1 m from the collimator surface. For both proton energies, positron distribution in the phantom could be imaged by the gamma camera with 10-min acquisition. The lengths of the range of protons measured from the images were almost identical to the simulation results. Conclusions These results indicate that the developed high-energy gamma camera is useful for imaging positron distributions in proton therapy. Keywords Imaging
Proton therapy Positron Gamma camera
Introduction
S. Yamamoto (&) M. Komori Y. Morishita S. Okumura Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami, Higashi-Ku, Nagoya 461-8673, Japan e-mail: [email protected] T. Toshito Department of Proton Therapy Physics, Nagoya Proton Therapy Center, Nagoya City West Medical Center, Nagoya, Japan M. Yamaguchi Y. Saito Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency (JAEA), Takasaki, Gunma, Japan N. Kawachi S. Fujimaki Quantum Beam Science Center, Japan Atomic Energy Agency (JAEA), Takasaki, Gunma, Japan
In proton therapy, positron radionuclides such as 11C and O are generated by the nuclear reactions with protons and stable radionuclides in the subject [1–3]. These protoninduced positrons are used for monitoring the proton beam distribution after therapy to estimate the range of proton in the subjects. Usually, positron emission tomography (PET) systems installed near or inside the proton beam facility are used for this imaging. Commercial PET/CT systems installed nea
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