Monte Carlo Simulation of Prostate Intensity Modulated Radiotherapy Using PRIMO Software: A Feasibility Study

Introduction: Nowadays Intensity Modulated Radiotherapy (IMRT) is a common method for treating prostate cancers. Must of the Monte Carlo software cannot simulate the IMRT procedures due to inability of these soft wares to simulate the multi leaf collimator (MLC) positions or movements. A new user-friendly software based on the PENELOPE Monte Carlo code named PRIMO was published recently. This software can simulate the MLC positions in IMRT procedures. The aim of this study was to simulate the prostate IMRT fields and calculate the dose on a physical phantom. Materials and Methods: PRIMO software was used to simulate the Varian clinic 600c and Varian 80L MLC. The MLC movement was simulated in PRIMO using control points that can be obtained from the treatment planning software (TPS). A CT scans of Delta 4 phantom (ScandiDos, Sweden) were imported to the PRIMO and typical 9 fields IMRT planning was simulated on this phantom. Empirical measurements were done using Delta 4 phantom with its inside embedded diode dosimeters and computer software. Dose comparison between the simulation and empirical measurement was done using gamma evaluation method (2%, 2mm) in PRIMO software module. Results: Simulated results were in good agreement with measurement. 99% of gamma points were lower than 1. Anterior, lateral and anterior oblique fields were in complete agreement with simulation, i.e. 100% of gamma points <1. Posterior and posterior oblique fields had a few gamma points >1. Conclusion: PRIMO software can precisely simulate the prostate IMRT in relevant clinical accessible time. The difference between simulation and measurement in posterior fields may be due to the treatment couch that was not simulated in PRIMO.