A maximum likelihood method for high resolution proton radiography/proton CT.
Multiple Coulomb scattering (MCS) is the largest contributor to blurring in proton imaging. In this work, we developed a maximum likelihood least squares estimator that improves proton radiography's spatial resolution. The water equivalent thickness (WET) through projections defined from the source to the detector pixels were estimated such that they maximizes the likelihood of the energy loss of every proton crossing the volume. The length spent in each projection was calculated through the optimized cubic spline path estimate. The proton radiographies were produced using Geant4 simulations. Three phantoms were studied here: a slanted cube in a tank of water to measure 2D spatial resolution, a voxelized head phantom for clinical performance evaluation as well as a parametric Catphan phantom (CTP528) for 3D spatial resolution. Two proton beam configurations were used: a parallel and a conical beam. Proton beams of 200 and 330 MeV were simulated to acquire the radiography. Spatial resolution is increased from 2.44 lp cm-1to 4.53 lp cm-1in the 200 MeV beam and from 3.49 lp cm-1to 5.76 lp cm-1in the 330 MeV beam. Beam configurations do not affect the reconstructed spatial resolution as investigated between a radiography acquired with the parallel (3.49 lp cm-1to 5.76 lp cm-1) or conical beam (from 3.49 lp cm-1to 5.56 lp cm-1). The improved images were then used as input in a photon tomography algorithm. The proton CT reconstruction of the Catphan phantom shows high spatial resolution (from 2.79 to 5.55 lp cm-1for the parallel beam and from 3.03 to 5.15 lp cm-1for the conical beam) and the reconstruction of the head phantom, although qualitative, shows high contrast in the gradient region. The proposed formulation of the optimization demonstrates serious potential to increase the spatial resolution (up by 65[Formula: see text]) in proton radiography and greatly accelerate proton computed tomography reconstruction.
Département de physique, de génie physique et d'optique et Centre de recherche sur le cancer, Université Laval, Québec, Canada. Département de radio-oncologie et CRCHU de Québec, CHU de Québec, QC, Canada. Department of Radiation Oncology, Francis H. Burr Proton Therapy Center Massachusetts General Hospital (MGH), Boston, MA, USA.
Charles-Antoine
CA
Collins-Fekete
Sébastien
S
Brousmiche
Stephen K N
SK
Portillo
Luc
L
Beaulieu
Joao
J
Seco
D000465:Algorithms; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016013:Likelihood Functions; D019047:Phantoms, Imaging; D011522:Protons; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods*
D011522:Protons