In heavy ion radiotherapy, pristine C-12 beams are usually widened a few mm (FWHM) along the beam axis, before the actual spread out Bragg peak (SOBP) is build. The pristine beam widening is commonly performed with a ripple filter, known from the facility at GSI (Darmstadt) and at HIT (Heidelberg). The ripple filter at GSI and HIT consists of several wedge like structures, which widens the Bragg-peak up to e.g. 3 mm. For Monte Carlo simulations of C-12 therapy, the exact setup, including the ripple filter needs to be simulated. In the Monte Carlo particle transport program FLUKA, the ripple filter can be realized in several ways. The most simplistic version is to apply the ripples as simple triangles. More elaborate version would account for the exact structure, but the drawback is that this will bloat the FLUKA input file with vast amounts of bodys which needs to be included in the geometrical setup. Since the ripple filter is a periodic geometry, one could use the LATTIC card with advantage, but here we shall take a Monte Carlo based approach istead. The advantage of this method is that our input file merely contains one body as the ripple filter, which can be a flat slab (or any other arbitrary geometry). In addition, a very small user routine is invoked. Apart of describing the method, we show that this method achieves practically identical results compared to a direct implementation of the ripple filter.
partikelterapi; monte carlo simulationer; particle therapy