Dose Calculations in Radiation Therapy Based on Patient Models Using the Geant4 Monte Carlo Code
Monte Carlo methods are considered to be the most accurate methods used to calculate the absorbed dose in the patient in radiation therapy. Many treatment-planning studies have shown that there are signi cant differences between the results from Monte Carlo dose
calculation and the results from conventional methods, such as pencil beam and convolution/superposition algorithms.1,2
Monte Carlo simulations are generally more accurate than analytical algorithms because they take into account the physics of particle interactions on a particle-by-particle basis. This is done using theoretical models or experimental cross-section data for electromagnetic and nuclear interactions. One has to keep in mind that the reliability of Monte Carlo transport calculations depends on the accuracy of the underlying physics data. Monte Carlo simulations consider tissue inhomogeneities by using speci c material properties, e.g., elemental composition, electron density, mass density, or ionization potential. The appropriate position of inhomogeneities along the beam path and its scattering effects are modeled. Secondary particles can be tracked, which, for example, allows the appropriate consideration of nuclear fragments.