The Studies Of Monte Carlo Dose Calculation Algorithm For Photon Beams And Physical Characteristics Of X-rays Scattered By Phantom

Purpose: To develop some simple but accurate photon beam models (for Co⁶⁰ therapy source and linear accelerator). By combined these models with EGS4, to implement a high precise Monte Carlo dose algorithm for photon beams and to investigate the physical characteristics of x-rays scattered by phantom and reaching the imaging detector. Material and Method: Multiple-source (2-3) models were developed through analyzing the simulation results published in literatures for Co⁶⁰ therapy source and linear accelerator x-ray source. These models were used to reconstruct the phase-space data in phantom surface for photon beams under any irradiated conditions. Based on the multiple-source models and EGS4, a Monte Carlo dose calculation algorithm and a Monte Carlo application code named PhanScatter, which was used to study the physical characteristics of x-rays scattered by phantom and reaching the imaging detector, were implemented. The dose distribution in homogeneous and heterogeneous phantoms for various fields and source-surface distances were calculated and compared with the measured results. The energy spectrum, fluences and average energy of primary x( γ )-rays and x( γ )-rays scattered by phantom in the detector plane were investigated. Scatter fractions under different scattering geometry conditions were also calculated.Results: The Monte Carlo calculations were compared with the measured data agreements for the depth dose curves were better than 1%. for beam profiles were better than 2%. The heterogeneity correction factors for layered-lung and -bone phantoms agreed respectively within 2% and 1% with the results calculated and measured by other authors. Energy spectrum, fluences and average energies for primary and each kind of scatter rays and scatter fractions in the detector plane were obtained. The influences by the scattering geometry were studied. The scatter fractions calculated by Monte Carlo simulations were found to be in good agreement with the ionization chamber results measured by other...