Joint application of perl scripts and MCNPX in solving the dynamic-geometry related problems in proton beam radiotherapy

The Monte Carlo code MCNPX has been verified to be a suitable tool in predicting dose distributions in proton therapy problems. In the passive-scattering treatment technique, a range modulation wheel rotating at a fixed rate in the treatment process is used to generate a spread-out Bragg peak depth-dose distribution. This dynamic geometry cannot be modeled in the simulation of MCNPX. In this study, a so-called 'replacing dynamic by static' method was adopted to solve this problem. This method was implemented by a script—'mcnp_–pstudy,' written in Perl programming language, which was used to set up a series of MCNPX input files, each of which contains the parameters of a specified step of the wheel, and invoke MCNPX to simulate each problem successively. The other Perl script—'mcnp_–pstudy,' was used to merge all the separate simulation results into one file containing the simulation results that are equivalent to a 'dynamic' simulation. The simulation results such as particle fluence and dose distributions were obtained from this study. This study provided an example of joint application of Perl scripts and MCNPX. (author)