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Proton Therapy Dosimetry by Using the Scintillation of Glass and Plastic Bare Optical Fibers

A Darafsheh

A Darafsheh1*, R Taleei2 , A Kassaee1 , J Finlay1 , (1) University of Pennsylvania, Philadelphia, PA, (2) UT Southwestern Medical Center, Dallas, TX


SU-I-GPD-T-138 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the origin of the signal responsible for proton therapy fiber optic dosimetry using bare optical fibers.

Methods: Bare optical fibers made of silica glass and poly(methyl methacrylate) (PMMA) were embedded in solid water phantoms and irradiated with proton therapy beams with 100-225 MeV energies. Optical spectroscopy was performed by a CCD-coupled spectrometer to analyze the emission spectrum of the fiber tip across the visible range of 400-700 nm. Monte Carlo simulation was performed by using FLUKA Monte Carlo code to simulate Čerenkov radiation generation and ionizing radiation dose deposition in the fibers as a function of depth in phantom.

Results: The experimental spectra of the irradiated silica and PMMA fibers show spectral shape different from that of Čerenkov radiation. Specifically, the spectrum of the silica fiber shows two distinct peaks at 460 and 650 nm, whose origins are connected to the point defects of the silica: oxygen-deficiency centers (ODC) and non-bridging oxygen hole centers (NBOHC), respectively. The ratio of the intensities of these peaks was not constant at various depths. The spectrum of the PMMA fiber shows a continuous spectrum with a peak at 410 nm whose origin is connected with the fluorescence of the fiber material. Monte Carlo simulation results confirmed the experimental observations that Čerenkov radiation cannot be the responsible signal for proton therapy dose measurement using bare optical fibers.

Conclusion: We showed that Čerenkov radiation is not the responsible signal for proton therapy dosimetry using bare optical fibers. The fact that the ratio of the signal peak intensities originated from the silica fiber varies with the depth suggests a dependency on the linear energy transfer (LET) of the beam and can be carefully examined for LET sensing.

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