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Characterization of a Fiber-Taper CCD Photo-Counting System for Plastic Scintillation Dosimetry and Comparison to the Traditional Lens System

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L Gagnon

L Gagnon1*, S Beddar2, L Beaulieu1, (1) Centre Hospitalier Universitaire de Quebec, Quebec, Qc, (2) MD Anderson Cancer Ctr., Houston, TX

TU-C-108-8 Tuesday 10:30AM - 12:30PM Room: 108

Purpose: To build a lens-less CCD photo-counting system for plastic scintillation dosimeters (PSDs), characterize its signal-to-noise ratio (SNR), its dose and dose-rate sensitivity, and compare it to traditional CCD+lens optical systems.

Methods: The detector used in this study is made of a 1 mm diameter by 2 mm long BCF60 scintillating-fiber coupled to a 2.6 meters clear plastic fiber. This PSD is coupled to two different photon-counting systems. The first is composed of a fiber-taper system (FTS) of a 2048 x 2048 pixels attached to an uncooled Alta (Apogee) 4020 polychromatic CCD-camera and a second one consisting of a 1600 x 1200 pixels, Alta (Apogee) 2020 polychromatic CCD-camera (cooled to -18°C) using a 50 mm lens of F#=1. The same identical dose measurements were made under the same irradiation conditions. For both systems, the chromatic Cerenkov removal method is used to account for the stem effects.

Results: The FTS increases the light collection by a factor of 4. This gain is possible because we are no longer restricted by the geometric limitation or the optical aberration of a lens system. Despite a difference of 45°C in operating temperature, we observed a SNR 1.8 times higher. This produces a good stability of measure vs. integration time with at most 1% difference on low-dose measurements. This also reduces by at least a factor of 2 the uncertainties, allowing us to realize low-dose measurements of 1.0 and 0.5 cGy with accuracy of 3.4% and 5.6% vs. 5.8% and 15.9% for the lens-based system.

Conclusion: This study demonstrates the superiority of the simpler FTS over a lens-based system. It opens the possibility of using PSDs of smaller radii (125 micron) to obtain greater spatial resolution. Reducing the size of PSDs could further simplify their use for in-vivo monitoring and small field dosimetry.

Funding Support, Disclosures, and Conflict of Interest: Development and funding supported by Standard Imaging.

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