title: Monitoring of positron using high-energy gamma camera for proton therapy.
abstract: OBJECTIVE
  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 × 0.85 mm × 10 mm Ce:Gd3Al2Ga3O12 (GAGG) pixels arranged in 20 × 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 × 35 cm × 5 cm plastic phantom 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 × 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.
authors.affiliation: Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami, Higashi-Ku, Nagoya, 461-8673, Japan, s-yama@met.nagoya-u.ac.jp.
authors.forename: Seiichi
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Toshito
authors.forename: Masataka
authors.initials: M
authors.lastname: Komori
authors.forename: Yuki
authors.initials: Y
authors.lastname: Morishita
authors.forename: Satoshi
authors.initials: S
authors.lastname: Okumura
authors.forename: Mitsutaka
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Saito
authors.forename: Naoki
authors.initials: N
authors.lastname: Kawachi
authors.forename: Shu
authors.initials: S
authors.lastname: Fujimaki
mesh_terms: D004583:Electrons; D004867:Equipment Design; D015902:Gamma Cameras; D006801:Humans; D019047:Phantoms, Imaging; D061766:Proton Therapy / Q000295:instrumentation* / Q000379:methods*; D012979:Sodium Radioisotopes
chemical_list: D012979:Sodium Radioisotopes