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Characterization of a Commercial Photodiode Based Plastic Scintillation Detector Prototype

L Wootton

L Wootton1*, D Klein1, C Bonde2, E Adams2, D Schmidt2, L Beaulieu3, S Beddar1, (1)UT MD Anderson Cancer Center, Houston, TX, (2) Standard Imaging Inc., Middleton, Wisconsin, (3) Centre Hospitalier Univ de Quebec, Quebec, QC

TU-A-BRB-6 Tuesday 8:00:00 AM - 9:55:00 AM Room: Ballroom B

Purpose: The purpose of this work is to characterize a commercial plastic scintillation detector (PSD) prototype that uses a photodiode to convert scintillation light to an electronic signal that can be measured with an electrometer. We tested the reproducibility of the detector as well as its accuracy.

Methods: The detector consists of 3 mm of scintillating fiber 1 mm in diameter connected to a photodiode via approximately 2 m of optical fiber. We tested the reproducibility of the detector by making daily measurements in a cobalt beam. We then verified the accuracy of the detector by measuring percent depth dose (PDD) curves on a linac for two photon and electron energies. The measurements were compared to commissioning data (measured with an ionization chamber) to quantify the accuracy of the detector.

Results: Over the course of ten days the mean dose the detector measured varied by 0.16% (1 standard deviation). The individual measurements on specific days varied as much as 0.27% and as little as 0.09%. PDD curves obtained with the detector differed from commissioning data by less than 0.6% for both photon energies. For both electron energies, the detector results differed from commissioning data less than 3% before the steep dose gradient towards the end of the electron range. In the dose falloff the difference was as great as 8% (likely due to positioning errors).

Conclusions: This new photodiode based PSD exhibited a very high level of reproducibility both in terms of individual measurements and average measurements on different days. Depth dose curves measured with the PSD in photon and electron beams demonstrated excellent agreement with machine commissioning data, validating the accuracy of this detector as well confirming that it is an energy independent detector.

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