title: Proton-induced x-ray fluorescence CT imaging.
abstract: OBJECTIVE
  To demonstrate the feasibility of proton-induced x-ray fluorescence CT (pXFCT) imaging of gold in a small animal sized object by means of experiments and Monte Carlo (MC) simulations.
  
  
  METHODS
  First, proton-induced gold x-ray fluorescence (pXRF) was measured as a function of gold concentration. Vials of 2.2 cm in diameter filled with 0%-5% Au solutions were irradiated with a 220 MeV proton beam and x-ray fluorescence induced by the interaction of protons, and Au was detected with a 3 × 3 mm(2) CdTe detector placed at 90° with respect to the incident proton beam at a distance of 45 cm from the vials. Second, a 7-cm diameter water phantom containing three 2.2-diameter vials with 3%-5% Au solutions was imaged with a 7-mm FWHM 220 MeV proton beam in a first generation CT scanning geometry. X-rays scattered perpendicular to the incident proton beam were acquired with the CdTe detector placed at 45 cm from the phantom positioned on a translation/rotation stage. Twenty one translational steps spaced by 3 mm at each of 36 projection angles spaced by 10° were acquired, and pXFCT images of the phantom were reconstructed with filtered back projection. A simplified geometry of the experimental data acquisition setup was modeled with the MC TOPAS code, and simulation results were compared to the experimental data.
  
  
  RESULTS
  A linear relationship between gold pXRF and gold concentration was observed in both experimental and MC simulation data (R(2) > 0.99). All Au vials were apparent in the experimental and simulated pXFCT images. Specifically, the 3% Au vial was detectable in the experimental [contrast-to-noise ratio (CNR) = 5.8] and simulated (CNR = 11.5) pXFCT image. Due to fluorescence x-ray attenuation in the higher concentration vials, the 4% and 5% Au contrast were underestimated by 10% and 15%, respectively, in both the experimental and simulated pXFCT images.
  
  
  CONCLUSIONS
  Proton-induced x-ray fluorescence CT imaging of 3%-5% gold solutions in a small animal sized water phantom has been demonstrated for the first time by means of experiments and MC simulations.
authors: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847 and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
authors: Magdalena
authors: M
authors: Bazalova-Carter
authors: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors: Moiz
authors: M
authors: Ahmad
authors: Department of Medical Physics, Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo 060-8648, Japan and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
authors: Taeko
authors: T
authors: Matsuura
authors: Department of Medical Physics, Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo 060-8648, Japan and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
authors: Seishin
authors: S
authors: Takao
authors: Department of Medical Physics, Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo 060-8648, Japan.
authors: Yuto
authors: Y
authors: Matsuo
authors: Department of Radiology, Stanford University, Stanford, California 94305.
authors: Rebecca
authors: R
authors: Fahrig
authors: Department of Medical Physics, Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo 060-8648, Japan and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
authors: Hiroki
authors: H
authors: Shirato
authors: Department of Medical Physics, Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo 060-8648, Japan and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
authors: Kikuo
authors: K
authors: Umegaki
authors: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847 and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
authors: Lei
authors: L
authors: Xing
mesh_terms: D000818:Animals; D007091:Image Processing, Computer-Assisted; D009010:Monte Carlo Method; D061848:Optical Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011522:Protons; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014867:Water
chemical_list: D011522:Protons; D014867:Water
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