| A technique for treatment of total skin irradiation was simulated using the Monte Carlo method. By application of this simulation, optimization of the Total Skin Electron Therapy (TSET) technique was accomplished. The purpose of the optimization process was to select the properties of the optimal TSET secondary scatterer. The optimization process was divided into four steps. First, the geometry of the treatment head of a Phillips SL-20 linear accelerator and the geometry of the TSET technique were simulated. Using a combination of the EGS4 Monte Carlo code system, geometry routines, and a package of variance reduction techniques, spectrum of the electron beam, at the exit window of the treatment head and at the treatment plane (located at 300 cm), was calculated. Second, to confirm the accuracy of calculations, the calculated depth dose curves, field uniformity and bremsstrahlung contamination for a control scatterer were compared to the measurement values. Third, a group of materials were selected to perform as a candidate for the optimal TSET scatterer. The treatment field characteristics produced by these materials were calculated and the optimal scatterer was selected. Forth, selection of the optimal scatterer was confirmed by way of physical measurements.; Physical measurements showed that the EGS4 Monte Carlo code system, together with the TSET user code, developed in this research, simulated the TSET technique accurately. However there were some problem areas. The central axis surface dose was underestimated by simulations and there was inconsistency associated with radial distribution of bremsstrahlung contamination.; Monte Carlo simulation of the TSET technique predicted a 0.059 mm thickness of lead as the optimal scatterer. This scatterer was predicted to produce a minimum uniformity of 73%, a d{dollar}sb{lcub}80%{rcub}{dollar} of between 1.8-2.1 cm and a 30% increase in dose rate (as compared to the control scatterer). Moreover, the Monte Carlo simulations TSET technique and different scattering materials demonstrated that a TSET scatterer controls the energy loss by way of its atomic number and the dose rate by way of its thickness. For a specific energy loss, however, field uniformity and bremsstrahlung contamination are not influenced noticeably by the properties of the scatterer. |
