[en] For the development of Monte Carlo (MC)-based dosimetric quality assurance (QA) tool for IMRT, multi-leaf collimator (MLC) model was constructed. Leakage radiation through the MLC leaves was simulated with this model as a preliminary step. Complicated structure of MLC leaves was developed for the Varian 80-leaf MLC using the Electron Gamma Shower version 4 (EGS4) MC program for 6 MV photon beam. This was then used to calculate dose profiles for an MLC fully blocked 10x10 cm² field at a depth of 5 cm in the water phantom. The energy spectra of incident photons were sampled from the published data of Sheikh-Bagheri et al. Obtained profiles had both of concavities and convexities. The intervals between adjacent peaks were from 0.9 to 1.1 cm, which agreed well to the actual thickness of 1 cm. The intensities of leakage radiations were not dependent on a location in a field. These results indicated the possibility that the MLC model developed in this study is valid. (author)