title: Variance reduction techniques for fast Monte Carlo CBCT scatter correction calculations.
abstract: Several variance reduction techniques improving the efficiency of the Monte Carlo estimation of the scatter contribution to a cone beam computed tomography (CBCT) scan were implemented in egs_ctct, an EGSnrc-based application for CBCT-related calculations. The largest impact on the efficiency comes from the splitting + Russian Roulette techniques which are described in detail. The fixed splitting technique is outperformed by both the position-dependent importance splitting (PDIS) and the region-dependent importance splitting (RDIS). The superiority of PDIS over RDIS observed for a water phantom with bone inserts is not observed when applying these techniques to a more realistic human chest phantom. A maximum efficiency improvement of several orders of magnitude over an analog calculation is obtained. A scatter calculation combining the reported efficiency gain with a smoothing algorithm is already in the proximity of being of practical use if a medium size computer cluster is available.
authors.affiliation: Ionizing Radiation Standards, National Research Council of Canada, Ottawa, Canada. mainegra@irs.phy.nrc.ca
authors.forename: Ernesto
authors.initials: E
authors.lastname: Mainegra-Hing
authors.forename: Iwan
authors.initials: I
authors.lastname: Kawrakow
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D013902:Radiography, Thoracic / Q000379:methods; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012984:Software; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water