Characterization of lateral dose distribution of proton beams using the Monte Carlo technique

Introduction:the study of dose deposition in tissue is a very complex task and can be solved with the Monte Carlo technique. nevertheless this solution cannot be adopted for treatment planning yet because, despite its reliability, it is not sufficiently fast for the clinical applications. In particular, the parametrization of the lateral dose profile is an substantial issue in this context.Methods:In this study, Gate Monte Carlo simulation code was used to compute absorbed dose and fluence of protons in a water cubic phantom for the clinical energy range. In the current study, after validating the Gate code, as a first approach we measured the lateral beam profiles of scanned proton pencil beams at different energies and depths in body tissue elements. We then tried to characterize the lateral dose distribution of proton beams in the therapeutic energy range.Results:After calculating the lateral dose distribution, lateral dose profiles and 2D dose distributions were drawn. Then, using these lateral dose curves, FWHM (Full width at half maximum) and the lateral penumbra (80% to 20%) were obtained at the depths corresponding to the location of Bragg peaks (maximum dose) for all energies. It was observed that with increasing the incident beam energy, FWHM and W(80-20) are roughly expanded as a second degree function with their own constant parameters. For example, the FWHM value of 5.7 mm in 50 MeV changes to about 13.5 mm in 200 MeV.

Keywords:

Gate code , Monte Carlo simulation , proton therapy , lateral dose.