Monte Carlo simulation of ripple filters designed for proton and carbon ion beams in hadrontherapy with active scanning technique

Proton and carbon ion beams have a very sharp Bragg peak. For proton beams of energies smaller than 100 MeV, fitting with a gaussian the region of the maximum of the Bragg peak, we can measure a sigma smaller than 1mm, while for carbon ion beams, the sigma measured in the same way is smaller than 1mm for energies up to 360 MeV. In order to use proton and carbon ion beams in hadrontherapy and to achieve an acceptable homogeneity of the SOBP, the peaks need to be broaden at least few millimeters by means of a properly designed ripple filter. The use of a ripple filter is mandatory in particular in conjunction with active scanning techniques for dose delivery, where it helps to reduce the numbers of energy switches necessary to obtain a smooth SOBP, leading also to shorter overall irradiation times. We studied the impact of the design of the ripple filter on the uniformity of dose in the SOBP region by means of Monte Carlo simulations, implemented using the package Geant4. We simulated the beam delivery line supporting both proton and carbon ion beams using different energies of the beams. We compared the effect of different kind of ripple filters and their advantages.