INSTITUTE OF PHYSICS PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 49 (2004) 4897–4917 PII: S0031-9155(04)77842-2 Monte Carlo simulation of x-ray spectra in diagnostic radiology and mammography using MCNP4C M R Ay 1,2 , M Shahriari 3 , S Sarkar 4 , M Adib 5 and H Zaidi 2 1 Department of Physics and Nuclear Sciences, AmirKabir University of Technology, Tehran, Iran 2 Division of Nuclear Medicine, Geneva University Hospital, 1211 Geneva, Switzerland 3 Department of Nuclear Engineering, Shahid Beheshti University, Tehran, Iran 4 Department of Medical Physics, Tehran University of Medical Science, Tehran, Iran 5 TPP Co., GE Medical Systems, Iran Authorized Distributor, Tehran, Iran E-mail: farshid.ay@tppgems.com Received 16 March 2004 Published 8 October 2004 Online at stacks.iop.org/PMB/49/4897 doi:10.1088/0031-9155/49/21/004 Abstract The general purpose Monte Carlo N-particle radiation transport computer code (MCNP4C) was used for the simulation of x-ray spectra in diagnostic radiology and mammography. The electrons were transported until they slow down and stop in the target. Both bremsstrahlung and characteristic x-ray production were considered in this work. We focus on the simulation of various target/filter combinations to investigate the effect of tube voltage, target material and filter thickness on x-ray spectra in the diagnostic radiology and mammography energy ranges. The simulated x-ray spectra were compared with experimental measurements and spectra calculated by IPEM report number 78. In addition, the anode heel effect and off-axis x-ray spectra were assessed for different anode angles and target materials and the results were compared with EGS4- based Monte Carlo simulations and measured data. Quantitative evaluation of the differences between our Monte Carlo simulated and comparison spectra was performed using student’s t-test statistical analysis. Generally, there is a good agreement between the simulated x-ray and comparison spectra, although there are systematic differences between the simulated and reference spectra especially in the K-characteristic x-rays intensity. Nevertheless, no statistically significant differences have been observed between IPEM spectra and the simulated spectra. It has been shown that the difference between MCNP simulated spectra and IPEM spectra in the low energy range is the result of the overestimation of characteristic photons following the normalization procedure. The transmission curves produced by MCNP4C have good agreement with the IPEM report especially for tube voltages of 50 kV and 80 kV. The systematic discrepancy for higher tube voltages is the result of systematic differences between the corresponding spectra. (Some figures in this article are in colour only in the electronic version) 0031-9155/04/214897+21$30.00 © 2004 IOP Publishing Ltd Printed in the UK 4897