title: A hybrid approach for rapid, accurate, and direct kilovoltage radiation dose calculations in CT voxel space.
abstract: OBJECTIVE
  To develop and validate a fast and accurate method that uses computed tomography (CT) voxel data to estimate absorbed radiation dose at a point of interest (POI) or series of POIs from a kilovoltage (kV) imaging procedure.
  
  
  METHODS
  The authors developed an approach that computes absorbed radiation dose at a POI by numerically evaluating the linear Boltzmann transport equation (LBTE) using a combination of deterministic and Monte Carlo (MC) techniques. This hybrid approach accounts for material heterogeneity with a level of accuracy comparable to the general MC algorithms. Also, the dose at a POI is computed within seconds using the Intel Core i7 CPU 920 2.67 GHz quad core architecture, and the calculations are performed using CT voxel data, making it flexible and feasible for clinical applications. To validate the method, the authors constructed and acquired a CT scan of a heterogeneous block phantom consisting of a succession of slab densities: Tissue (1.29 cm), bone (2.42 cm), lung (4.84 cm), bone (1.37 cm), and tissue (4.84 cm). Using the hybrid transport method, the authors computed the absorbed doses at a set of points along the central axis and x direction of the phantom for an isotropic 125 kVp photon spectral point source located along the central axis 92.7 cm above the phantom surface. The accuracy of the results was compared to those computed with MCNP, which was cross-validated with EGSnrc, and served as the benchmark for validation.
  
  
  RESULTS
  The error in the depth dose ranged from -1.45% to +1.39% with a mean and standard deviation of -0.12% and 0.66%, respectively. The error in the x profile ranged from -1.3% to +0.9%, with standard deviations of -0.3% and 0.5%, respectively. The number of photons required to achieve these results was 1 x 10(6).
  
  
  CONCLUSIONS
  The voxel-based hybrid method evaluates the LBTE rapidly and accurately to estimate the absorbed x-ray dose at any POI or series of POIs from a kV imaging procedure.
authors.affiliation: Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Alexei
authors.initials: A
authors.lastname: Kouznetsov
authors.forename: Mauro
authors.initials: M
authors.lastname: Tambasco
mesh_terms: D000042:Absorption; D003196:Computer Graphics; D006801:Humans; D009010:Monte Carlo Method; D017785:Photons; D011829:Radiation Dosage; D015203:Reproducibility of Results; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D035501:Uncertainty; D014584:User-Computer Interface