SU‐E‐T‐610: Phosphor‐Based Fiber Optic Probes for Proton Beam Characterization

Abstract

Purpose:To investigate feasibility of using fiber optics probes with rare‐earth‐based phosphor tips for proton beam radiation dosimetry. We designed and fabricated a fiber probe with submillimeter resolution (<0.5 mm3) based on TbF3 phosphors and evaluated its performance for measurement of proton beam including profiles and range.Methods:The fiber optic probe with TbF3 phosphor tip, embedded in tissue‐mimicking phantoms was irradiated with double scattering proton beam with energy of 180 MeV. Luminescence spectroscopy was performed by a CCD‐coupled spectrograph to analyze the emission spectra of the fiber tip. In order to measure the spatial beam profile and percentage depth dose, we used singular value decomposition method to spectrally separate the phosphors ionoluminescence signal from the background Cerenkov radiation signal.Results:The spectra of the TbF3 fiber probe showed characteristic ionoluminescence emission peaks at 489, 542, 586, and 620 nm. By using singular value decomposition we found the contribution of the ionoluminescence signal to measure the percentage depth dose in phantoms and compared that with measurements performed with ion chamber. We observed quenching effect at the spread out Bragg peak region, manifested as under‐responding of the signal, due to the high LET of the beam. However, the beam profiles were not dramatically affected by the quenching effect.Conclusion:We have evaluated the performance of a fiber optic probe with submillimeter resolution for proton beam dosimetry. We demonstrated feasibility of spectral separation of the Cerenkov radiation from the collected signal. Such fiber probes can be used for measurements of proton beams profile and range. The experimental apparatus and spectroscopy method developed in this work provide a robust platform for characterization of proton‐irradiated nanophosphor particles for ultralow fluence photodynamic therapy or molecular imaging applications.