Measurement of scintillation responses of scintillation fibers for dose verification in proton therapy

Here, we report on the measurement of scintillation responses of scintillation fibers for precision dose verification in proton therapy. A detector equipped with two layers of 1-mm-thick scintillation fibers and 46-channel silicon photodiodes was constructed and tested with 45-MeV proton beams provided by the MC50 proton cyclotron at the Korea Institute of Radiological and Medical Science (KIRAMS). Scintillation responses of the detector for the protons were measured as a function of depth in an absorber made of PMMA (poly methyl methacrylate) and PET (polyester) films whose thicknesses varied from 0.148 to 2.0 g·cm ^-2. Quenching of the scintillation responses of the detector was evaluated by comparison of the data to the specific energy loss predicted by GEANT4-based simulations. The first-order parameter of the Birks model, kB, for scintillation fibers, as derived from the ratios of specific energy losses to scintillation responses, was (2.38 ± 0.17) × 10 ^-2.