Performance of a terbium doped gadolinium oxysulphide plastic optical fiber sensor in a flattening filter free setting: measurements and Monte Carlo simulation

Majed Alharbi; Michael Martyn; Sean Gillespie; Peter Woulfe; Sinead O'Keeffe; Mark Foley

doi:10.1117/12.2509441

27 February 2019 Performance of a terbium doped gadolinium oxysulphide plastic optical fiber sensor in a flattening filter free setting: measurements and Monte Carlo simulation

Majed Alharbi, Michael Martyn, Sean Gillespie, Peter Woulfe, Sinead O'Keeffe, Mark Foley

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Proceedings Volume 10872, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XIX; 108720P (2019) https://doi.org/10.1117/12.2509441
Event: SPIE BiOS, 2019, San Francisco, California, United States

Abstract

This paper presents an initial investigation into the depth dependence of an inorganic optical fibre sensor (OFS) based on physical measurements and Monte Carlo (MC) simulations, using a 6 MV flattening filter free (FFF) beam. The OFS was fabricated using an inorganic scintillating material (Gd₂O₂S:Tb), which was embedded in a cavity of diameter 700 μm, in a 1mm plastic optical fibre. Percentage depth dose (PDD) profiles were measured in a solid water phantom for three field sizes: 10×10 cm² , 4×4 cm² and 2×2 cm² . The OFS results were then compared to an ion chamber and the W1 plastic scintillator. A MC model of an Elekta Versa HD linear accelerator (linac) was developed using the MC software packages BEAMnrc and DOSXYZnrc and then used to simulate the Gd₂O₂S:Tb and polystyrene scintillators. The OFS measurements over-estimated the dose when compared to the ion chamber and the W1 measurements, across the investigated field sizes, by a maximum of 30%, 20% and 15% for 10×10 cm² , 4×4 cm² and 2×2 cm² , respectively. The MC simulations of the Gd₂O₂S:Tb and polystyrene scintillators were in good agreement with the W1 and ion chamber measurements, however, the OFS measurements were found to differ across all field sizes. Our results therefore indicate the need for further investigation into the overall contribution of the stem effect to the discrepancy between the OFS physical measurements and the ion chamber and the W1 measurements.

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Majed Alharbi, Michael Martyn, Sean Gillespie, Peter Woulfe, Sinead O'Keeffe, and Mark Foley "Performance of a terbium doped gadolinium oxysulphide plastic optical fiber sensor in a flattening filter free setting: measurements and Monte Carlo simulation", Proc. SPIE 10872, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XIX, 108720P (27 February 2019); https://doi.org/10.1117/12.2509441

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