Monitor unit calculation in electron therapy using Monte Carlo Simulation: a GUI for the phase-space field trimming

Purpose: We developed a graphical user interface (GUI) for electron phase-space field trimming using Monte Carlo simulations. This GUI can be used for monitor unit (MU) calculation in electron therapy. Methods: The GUI and electron field trimming algorithm were developed using MATLAB and C code. Phase-space files for the electron fields were generated using the EGSnrc code based on a Varian 21EX Linac with variables of applicator size, field size and energy. Verification of the alogrithm was carried out by comparing the relative output factor, which was used for MU calculation, predicted by Monte Carlo simulations and from actual measurements. Results: Our electron field trimming algorithm was found to be about five times faster than the original Monte Carlo simulation. Clinically, the GUI performed best when using voxel size ≥ 0.3 × 0.3 × 0.3 cm3, and field size larger than 2 cm in radius based on an acceptable deviation of 2%. Conclusion: A GUI for generating irregular field for MU calculation using Monte Carlo simulations was created as a user-friendly tool in electron therapy.