Abstract
Purpose:Different versions of MCNP code are widely used for dosimetry purposes. The purpose of this study is to compare different versions of the MCNP codes in dosimetric evaluation of different brachytherapy sources.Methods:The TG‐43 parameters such as dose rate constant, radial dose function, and anisotropy function of different brachytherapy sources, i.e. Pd‐103, I‐125, Ir‐192, and Cs‐137 were calculated in water phantom. The results obtained by three versions of Monte Carlo codes (MCNP4C, MCNPX, MCNP5) were compared for low and high energy brachytherapy sources. Then the cross section library of MCNP4C code was changed to ENDF/B‐VI release 8 which is used in MCNP5 and MCNPX codes. Finally, the TG‐43 parameters obtained using the MCNP4C‐revised code, were compared with other codes.Results:The results of these investigations indicate that for high energy sources, the differences in TG‐43 parameters between the codes are less than 1% for Ir‐192 and less than 0.5% for Cs‐137. However for low energy sources like I‐125 and Pd‐103, large discrepancies are observed in the g(r) values obtained by MCNP4C and the two other codes. The differences between g(r) values calculated using MCNP4C and MCNP5 at the distance of 6cm were found to be about 17% and 28% for I‐125 and Pd‐103 respectively. The results obtained with MCNP4C‐revised and MCNPX were similar. However, the maximum difference between the results obtained with the MCNP5 and MCNP4C‐revised codes was 2% at 6cm.Conclusion:The results indicate that using MCNP4C code for dosimetry of low energy brachytherapy sources can cause large errors in the results. Therefore it is recommended not to use this code for low energy sources, unless its cross section library is changed. Since the results obtained with MCNP4C‐revised and MCNPX were similar, it is concluded that the difference between MCNP4C and MCNPX is their cross section libraries.
Published Version
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