SU-E-T-296: Optimization of the Energy Selection System with Varying Magnetic Field for Laser-Accelerated Proton Beams.

PURPOSE Laser-based accelerated proton beams are unsuitable for clinical use because of their broad energy spectra. For this reason, it is essential to employ an energy selection system (ESS). The purpose of this study is to determine optimum parameters of the ESS which uses a varying magnetic field to generate Bragg-peak. METHODS We simulated an accelerated proton beams using radiation pressure acceleration mechanism with carbon-proton mixture target. The density ratio (n = 6) between the protons and the carbon ions is one of optimization parameters in determining the accelerating mechanisms. The ESS was implemented by the Geant4 Monte Carlo toolkit. In order to optimize the hole size and position of the energy selection collimator, and magnetic field at ESS, these parameters were simulated for acquiring energy and dose distributions by changing each values. RESULTS The proton energy distributions had a poly-energetic distribution after passing through the ESS. As the magnetic field was increased, the mean energy of the proton beams also was increased. Also as the hole size was increased, the energy bandwidth of proton passed through the ESS was increased. The hole size and position of the energy selection collimator were effectively optimized to 2 cm and 5 cm from the z-axis, respectively. CONCLUSIONS We simulated laser-accelerated proton beams using ESS for generation of Bragg-peak. Our results suggest that the ESS with magnetic field variation can effectively generate a Bragg-peak suitable for use in proton radiation therapy. Our ESS can be applied to pencil beam scanning proton therapy.