MCNP-FBSM: Development of MCNP/MCNPX Source Model for Simulation of Multi-Slice Fan-Beam X-Ray CT Scanners

A Monte Carlo Platform for Characterization of X-Ray Radiation Dose in CT Imaging

“…The most common MC codes are MCNP [ 5 ], GEANT [ 6 ], FLUKA [ 7 ], and EGSnrc [ 8 ]. None of these codes are optimized enough because of the lacking an optimized fan-beam CT source model [ 13 ]. This strongly decreases the efficiency of MC programs and the number of tracking photons [ 12 , 13 ].…”

“…However, an effective fan-beam source model for simulation of clinical CT scanner is still missing. Therefore, it has recently been devised and implemented in the subroutines of the MCNP code, which yielded a proper MCNP MC code for CT imaging called MCNP-FBSM [ 13 ]. MCNP-FBSM was designed to transport particle types present in the CT procedure, including photon and electron over a wide range of energies.…”

“…Akhavanallaf et al [ 12 ] developed an MCNP-based MC CT simulator for assessing in-phantom CT dose uncertainties. The primary step in the MC modeling of such scanners is the X-ray source simulation, where all of these codes are not optimized enough due to the lack of an optimized CT source model, removing the needs of the collimator for shaping beam into fan geometry [ 13 ]. This problem has fatally affected the execution time of MC simulation, accuracy and precision of outcomes [ 12 , 13 ].…”

“…The primary step in the MC modeling of such scanners is the X-ray source simulation, where all of these codes are not optimized enough due to the lack of an optimized CT source model, removing the needs of the collimator for shaping beam into fan geometry [ 13 ]. This problem has fatally affected the execution time of MC simulation, accuracy and precision of outcomes [ 12 , 13 ]. X-ray photons come from a bimodal focal spot profile [ 14 ] on the anode area, and then their directions are trimmed into fan geometry by lead leaves of the collimator.…”

“…To overcome this problem, source biasing technique is proposed to decrease the contribution of incoming photons in the outside of the field-of-view. There are at least three ways proposed to simulate a fan-beam CT source model in the MCNP code, including standard method, the cookie-cutter technique, and a bunch of pencil beams comprising many discrete point sources [ 13 ]. The only realistic estimation of reality is the standard source model, which is time-consuming even using source biasing [ 13 ] and thus to overcome the problem of particle starvation imposed by the collimator, a fan-beam CT source model called “ MCNP-FBSM ” has been proposed for calculation of imaging parameters [ 13 ].…”