Program Information
Characterization of Spectral Changes in Light Guides Used for Scintillation Dosimetry in Linear Accelerator Based Measurement Geometries
E. A. Simiele*, W. S. Culberson , L. A. DeWerd , Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI
Presentations
SU-I-GPD-T-549 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To characterize spectral changes in light guides used in scintillation detectors in linear accelerator based measurement geometries, and to determine the impacts of any spectral changes on the Cerenkov light ratio (CLR).
Methods: Five light guides (two PMMA, two silica, and one polystyrene), each 3 m in length, were used in this study. All measurements were performed with an Ocean Optics QE Pro spectrometer. Since the spectrometer was in the accelerator vault for all measurements, custom shielding was designed to minimize the impact of radiation noise on the measured spectra. Spectral measurements were made as a function of depth in phantom and fiber-beam angle in air in a custom-built PMMA jig. Due to the low signal, an optimization algorithm was developed to determine the optimal measurement parameters to balance fiber SNR and measurement uncertainty. The CLR was calculated from each spectrum by summing the signal in the wavelength range of 400 to 500 nm and dividing it by the total signal between 500 to 600 nm.
Results: The PMMA fibers showed nearly identical spectral responses for all measurements. The low-hydroxyl content silica fiber exhibited a strong fluorescence peak that was not observed in the other fibers. Qualitatively, all of the fibers showed no change in spectral shape with depth or fiber-beam angle. There was no significant change in the CLR with depth for the PMMA fibers, whereas the other fibers showed increasing trends in the CLR with depth. All of the fibers showed decreasing trends in the CLR with fiber-beam angle.
Conclusion: Contrary to previous works, no changes in spectral shape with depth or fiber-beam angle were observed. However, increasing trends were observed in the CLR with depth for three of the fibers and all of the fibers showed decreasing trends in the CLR with fiber-beam angle.
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