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Characterization of a Novel CCD Camera Based Imaging System for Radiochromic Film Dosimetry

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K Alexander

K Alexander1, T Olding2, G Salomons1,2, LJ Schreiner1,2*, (1) Queen's University, Kingston, Ontario, (2) Cancer Centre of Southeastern Ontario, Kingston, Ontario

SU-E-T-51 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
In this paper we present work to further develop and characterize a novel method of reading radiochromic film. The technique is benchmarked against imaging on a clinically used Epson 10000XL scanner, using well characterized standard dose deliveries and patient IMRT QA results.

Methods:
A purpose-built CCD camera-based film digitizer was designed and prototyped with Modus Medical (London, Ontario). The system consists of a camera mounted above a LED lightbox, interfaced with computer image acquisition software. The system was based on components of the Vista optical CT scanner (Modus Medical Devices Inc.) and looks to improve on the flat-bed scanner based dosimetry system, which suffer from film orientation dependence and non-uniform scanner sensitivity. Various characteristics imaging system performance were measured including: dependence on camera aperture size, spatial resolution, light scatter contamination, lightbox temperature variation effects, and signal-to-noise ratio (SNR). Dose readout accuracy has also been determined using films that have been imaged using white-light and colour lightbox illumination system. Results are compared with readout using the Epson scanner.

Results:
The new system provides fast, orientation independent readout of radiochromic film. High resolution (0.25 mm x 0.25 mm pixel size) and high signal-to-noise ratio (SNR = 280 for 230 cGy, 10x10 cm square field) images are obtained in 6.7 seconds, averaging 100 frames. A warm-up time of at least one hour stabilizes light output and eliminates temperature effects. The readout of all test films agree well (to within 1% dose difference over most of the film) to the dose determined by other approaches.

Conclusion:
This new imaging technique shows good promise to simplify and improve on existing film dosimetry readout. Further development towards a commercial system is currently underway with Modus Medical.

Funding Support, Disclosures, and Conflict of Interest: Research funding support provided by the Canadian Institutes of Health Research (CIHR)

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