Development of multilayered dose-verification detectors in particle therapy

Multilayered detectors composed of scintillation fibers and thin gaseous detectors have been studied for fast and precision dose measurement for dynamic-mode particle therapy. In the R&D of the dose measurement with scintillation fibers, a prototype detector composed of 10 scintillation-fiber layers operating in a signal processing and DAQ speed of 250 Hz was constructed and tested with 43-MeV protons provided by the MC50 proton cyclotron at the Korea Institute of Radiological and Medical Science (KIRAMS). The quantitative accuracy appearing in the spatial-distribution of the detector responses is on the order of 1%, which is quite satisfactory to verify beam-induced doses for the precision proton therapy. However, we propose development of a detector composed of multilayered thin gaseous ionization detectors for heavy-ion therapy, where the use of scintillation fibers would be restricted due to the nonlinearity of the scintillation-light yield to the energy loss. Furthermore, the speed of the signal-processing and DAQ to be applied to the new detector development was increased to 35 kHz to enhance the capability of the detector response to faster dynamic-mode beams wobbling with frequencies larger than 20 Hz. We also confirmed from the beam test at KIRAMS the excellent linear responses of the unit detectors to the beam current as well as the quantitative accuracy of about 1% appearing in the spatial distributions.