A comparison between EGS4 and MCNP computer modeling of an in vivo X-ray fluorescence system

Use of portable X-ray fluorescence (PXRF) in vivo as an alternative technique for the assessment of iron levels in patients with thalassemia and hemochromatosis

This work investigated the viability of the portable x-ray fluorescence (PXRF) technique as a means of measuring iron levels in patients suffering from thalassemia major (beta-thalassemia) and hereditary hemochromatosis (HH or Haemochromatosis) or other iron-overload conditions. Measurements were conducted at the University Hospital Blood Center and in the Laboratory of Applied Nuclear Physics at the State University of Londrina, Brazil. One thalassemia major patient and four healthy people were grouped. A PXRF system consisting of a Pu x-ray source and a SiPIN diode detector was used for measurements in vivo on the hand of each patient. The measuring system was calibrated with phantoms of aqueous solution doped with 15 to 150 ppm of iron. The duration of each measurement was 50 s. The detection limit (LLD) reached for iron was 13 ppm. The radiation dose on the skin was 10 mSv. The thalassemia patient presented 74 ± 6 ppm of iron, whereas the healthy people presented an average of 53 ± 5 ppm of iron. The results are in accord with the literature, which shows iron levels in the skin to be between 15 - 60 ppm for healthy people and between 70 - 150 ppm for thalassemia major patients. This work concluded that it is viable to apply the XRF methodology to follow thalassemia major and HH patients.

EGSnrc computer modelling of megavoltage x-rays transmission through some shielding materials used in radiotherapy

A computer user-code (TRANSMIT), based on the use of the EGSnrc Monte Carlo system, was developed to simulate the transmission of megavoltage x-rays through three different materials used for shielding purposes in radiotherapy. These materials are Lipowitz’s metal, lead and Rad-block. The simulations were performed for 4, 6 and 10 MV x-rays using narrow beam geometry in air. The linear attenuation coefficients, in cm–1, obtained from the simulated transmission curves for Lipowitz’s metal were 0.494, 0.470 and 0.452 for 4, 6 and 10 MV, respectively. For lead, the linear attenuation coefficients were 0.532, 0.507 and 0.483 for 4, 6 and 10 MV, respectively. For Rad-block, the linear attenuation coefficients were 0.561, 0.537 and 0.518 for 4, 6 and 10 MV, respectively. Comparison of the simulation results with experimental results reported in the literature gave a percent deviation <5% which indicates the validity of the simulation results. In addition, broad beam geometry calculations were performed for a variety of field sizes (10 × 10 cm2, 20 × 20 cm2 and 40 × 40 cm2) using the three different attenuators. The results showed that broad beam attenuation coefficients decreased with increased field size and photon energy. For Lipowitz’s metal, the difference in the linear attenuation coefficient data between the broad beam attenuation coefficient and the narrow beam value lies between 3.6% and 20% depending on x-ray energy and field size. Similarly, the difference between the broad beam attenuation coefficient and the narrow beam value for lead lies between 1.5% and 10.4%. For the Rad-block material, the difference lies between 0.53% and 6.8%.

Development of a computer code using the EGS4 Monte Carlo simulation system to evaluate the response of a NaI(Tl) detector to photons with energies below 300 keV

In this paper, the EGS4 Monte Carlo simulation system was used to develop a computer code for a study of the response of a NaI(Tl) detector exposed to gamma-rays with energies below 300 keV. This study comprised registration of the spectra of the incident rays and determination of the photo peaks. In addition, the probability of the K X-ray escape from a NaI(Tl) crystal and its dependence on the detector shape and volume were considered. The results of the Monte Carlo simulation are in good agreement with the experimental data (the estimated discrepancy is below 5%). This demonstrates a high efficiency of the used simulation code in quantifying the physical parameters that are difficult to evaluate by experimental methods.