Advanced designing of equipments for proton radiotherapy by using stereolithography

The new energy filter with multi-layer construction is developed by a new formative technique. A ridge-type structure is designed for the new filter having shape of a block. The outward of the block takes the size of 60 mm cube (15 layers). The total spread of Bragg peak depends on the variation of the absorber thickness (from 0 mm to 57 mm) and the water-equivalent length of the epoxy resin, which is set to 1.17 in the designing. The miniaturized structure of the filter is considered as a stack of thin rods (0.2 x 0.2 mm2 cross section) to form the ridge-shaped cell. As a simplified model of energy deposition in the human body, a water phantom is adopted in the calculation, which is considered as a stack of rods (4 x 4 mm2 cross section) similarly to the filter. It is confirmed by the experiments that the designing parameters of the filter can be decided by using the Monte Carlo calculation. By the designing and formative technique using the Monte Carlo calculation and stereolithography, advanced system with three-dimensional miniaturized structure can be realized for the charged particle radiotherapy. To construct the new energy filter, corn and pyramid are also usable as the shape of the unit cell in the filter. By using preliminary calculation, three-dimensional structure is designed for pyramid-type cells. Because changing of the thickness is distributed in a plane for the pyramide-type structure, it is supposed that the distortion of the dose distribution by the tilt angle, which is defined as the angle between the incident beam and the perpendicular axis of the new filter, is less than for ridge-type structure. (S.Y.)