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Characterization of Optically Stimulated Luminescent Dosimeters in a Simulated Fluoroscopy Beam

N Quails*, N Correa , I Barreto , C Carranza , L Rill , M Arreola , University of Florida, Gainesville, FL

Presentations

(Sunday, 7/29/2018) 1:00 PM - 1:55 PM

Room: Room 207

Purpose: To characterize the response of Optically Stimulated Luminescent Dosimeters (OSLDs) in a simulated fluoroscopy beam.

Methods: OSLD response to various energies, scatter, time, tube current, angulation, and dose rate were assessed. The half-value layers (HVL) of typical clinical beams in a fluoroscopic system driven by automatic brightness control (ABC) were measured and then replicated using a standard x-ray beam with aluminum (Al) and copper (Cu) filtration added.

Results: By comparing OSLD measurements with those from a 0.6 cc ion-chamber (IC), energy dependence was observed in the clinical range of 65-95 kVp, ranging from 7-24% for Fluoroscopic Mode 1 (1 mm Al + 0.4 mm Cu), 0-7% for Fluoroscopic Mode 2 (1 mm Al + 0.1 mm Cu), and 0-10% for Radio-graphic Mode (1 mm Al). Furthermore, differences in OSLD measurements due to scatter were observed to range from 0-4%,0-4%, and 3-12% for 65, 80, and 100 kVp in Fluoroscopic Mode 1, respectively, while for Fluoroscopic Mode 2, differences ranged from 1-5%, 4-9%, and 0-4% for 65, 80, and 100 kVp, respectively. OSLDs responded linearly (minimum R²=0.995) when compared to IC measurements with varied tube current or exposure time. OSLDs responded differently by 4-15% as a function of dose rate ranging from 136.2-304.4 µGy/s. Although OSLDs showed angular dependence in air, no dependence was observed with OSLDs placed in a cylindrical acrylic phantom. Correction factors were generated to account for OSLD dependence on energy (0.91-1.11), dose rate (0.85-1.04), angulation in air (0.87-1.04) and scatter (0.86-1.12) for different fluoroscopic modes and kVp settings.

Conclusion: Energy, scatter, dose rate, and angularity correction factors were generated for use of OSLDs in interventional fluoroscopic rooms. Large correction factors seem to be necessary for beams filtered with copper.

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