Three-dimensional conformal irradiation with a multilayer energy filter for proton therapy

The first experimental evidence of three-dimensional conformai irradiation is performed by using a new type of filter developed for charged particle radiotherapy. The new filter can yield a static irradiation field where the width of the spread-out Bragg peak is adjusted to the target as a two-dimensional continuous function in the transverse plane. The filter is made of many layers produced by using stereolithography. In the filter, a structure with two regions with different shaped miniaturized ridges is adopted to get a flat dose profile on the spread-out peak. A conformal field around a spherical target is realized by a filter that has a shape corresponding to the outward form of the target.