Modeling and Simulation of X-Rays Radiotherapy

Abstract

In this thesis, various concepts for Microbeam Radiation Therapy (MRT) technique were simulated and dosimetric calculations were performed with the Monte Carlo technique. In the first part, the dosimetric Monte Carlo calculations in the literature, performed with other codes were done with MCNPX to evaluate the suitability of the code for micrometric dosimetry at low X-ray energies. The calculated dose distributions were consistent with the ones that are given in the literature. In the second part, dose distribution calculations for bidirectional interlaced microbeam radiation therapy (BIMRT) were performed with realistic and homogenized head phantom models. The effect of the realistic phantom’s structure on dose distribution was evaluated. The parallel pattern of the microbeam arrays was preserved through the head phantom. As the dimensions of the target volume were increased, the valley doses increased with the number of microbeams. Simulations were performed for cases with and without Au contrast agent deposited in the target region and the surrounding tissue. The usage of the contrast agent provided a substantial increase in target dose. Short dose falloff widths at the edges of the targets were preserved for all cases. In the third part, the usage of a linear accelerator (linac) as the radiation source for the stereotactic MRT technique was evaluated. Unidirectional single beams and beam arrays were modeled in a cylindrical water phantom to observe the effects of X-ray energies, beam heights, beam thicknesses and beam intervals on dose distributions. Two orthogonally interlaced beam arrays were modeled in a detailed head phantom. Calculated dose distributions were compared with the ones calculated for the BIMRT. Five orthogonally interlaced beam array pairs were modeled in a mathematical head phantom. It was concluded that the advantages of the MRT technique would not be preserved with the usage of linac as the X-ray source.