EGS_cbct: Simulation of a fan beam CT and RMI phantom for measured HU verification.
BACKGROUND
A mathematical 3D model of an existing computed tomography (CT) scanner was created and used in the EGSnrc-based BEAMnrc and egs_cbct Monte Carlo codes. Simulated transmission dose profiles of a RMI-465 phantom were analysed to verify Hounsfield numbers against measured data obtained from the CT scanner.


METHODS
The modelled CT unit is based on the design of a Toshiba Aquilion 16 LB CT scanner. As a first step, BEAMnrc simulated the X-ray tube, filters, and secondary collimation to obtain phase space data of the X-ray beam. A bowtie filter was included to create a more uniform beam intensity and to remove the beam hardening effects. In a second step the Interactive Data Language (IDL) code was used to build an EGSPHANT file that contained the RMI phantom which was used in egs_cbct simulations. After simulation a series of profiles were sampled from the detector model and the Feldkamp-Davis-Kress (FDK) algorithm was used to reconstruct transversal images. The results were tested against measured data obtained from CT scans.


RESULTS
The egs_cbct code can be used for the simulation of a fan beam CT unit. The calculated bowtie filter ensured a uniform flux on the detectors. Good correlation between measured and simulated CT numbers was obtained.


CONCLUSIONS
In principle, Monte Carlo codes such as egs_cbct can model a fan beam CT unit. After reconstruction, the images contained Hounsfield values comparable to measured data.
Department of Medical Physics, University of the Free State, Bloemfontein 9300, South Africa. Electronic address: detevaneeden@gmail.com.
Dete
D
van Eeden
Department of Medical Physics, University of the Free State, Bloemfontein 9300, South Africa. Electronic address: DuPlessisFCP@ufs.ac.za.
Freek
F
du Plessis
D000465:Algorithms; D055592:Biophysical Phenomena; D003198:Computer Simulation; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000706:statistics & numerical data; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted; D015898:Tomography Scanners, X-Ray Computed; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*
Computed tomography; Monte Carlo; Simulation