Technique of Modification of the Bragg Peak of a Proton Beam for Radiotherapy

JINR in collaboration with the St. Petersburg-based Efremov Institute of Electrophysical Apparatus (NIIEFA) is developing a superconducting isochronous cyclotron MSC230, which is intended to conduct research in radiobiology and to develop proton flash radiotherapy techniques. In relation to this, formation of a high-intensity proton beam with the energy selectable in a range of 120–230 MeV, a dose rate of 50–100 Gy/s, and homogeneous in cross section with a diameter of 13–15 cm at the new accelerator is explored. Results of modeling by the Monte Carlo method and measurements of the depth-dose distributions of a proton beam, the energy spectrum of which is modified to obtain an extended homogeneous plateau at the end of the range (spread-out Bragg peak), are presented. This is achieved by using so-called ridge filters. A method for design and manufacturing ridge filters using a 3D printer that can change the length of the plateau in a fairly wide range of values by rotating it relative to the beam axis is presented. The results of the study lend a hope that two sets, each consisting of 5–6 such filters, will be able to span the entire required range of the Bragg peak plateau, and for all values of the selected energy.