MONTE-CARLO SIMULATION OF DOSE DISTRIBUTION IN ELECTRON-BEAM RADIOTHERAPY TREATMENT PLANNING

A three-dimensional Monte Carlo program, named "SHAPE", has been developed. It allows to simulate the electron beam irradiation of a patient, using X-ray computed tomography scans as input data. The particle transport is executed by EGS4 code and media data are calculated by its preprocessor PEGS4. The absorbed dose can be evaluated with high spatial resolution in every slice of the patient or in a restricted number of regions of interest called high-resolution zones. In the other zones where high resolution is not necessary for dosimetric purpose, the various organs are divided in several parallelepipeds of homogenous tissue having different sizes and the dose volume is calculated in each. With such a division, a considerable reduction of the CPU time is obtained without reduction of spatial resolution in the zones where the dose distribution is important. Details of the SHAPE algorithm and its preprocessor SCAN are presented. Some examples of dose distribution calculated in three-dimensional structures are also shown; they were obtained using computed tomography slices of an antropomorphous Alderson-Rando phantom. © 1990.