The influence of bowtie filtration on cone-beam CT image quality

Authors

  • Mail N.,

    1. Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada and Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada
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  • Moseley D. J.,

    1. Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada; Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada; and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M5G 2M9, Canada
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  • Siewerdsen J. H.,

    1. Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada; Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada; and Department of Radiation Oncology and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada
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  • Jaffray D. A.

    1. Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada; Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada; and Department of Radiation Oncology and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada
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    • a)

      Author to whom correspondence should be addressed. Address for correspondence: Radiation Physics, Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada. Telephone: 416-946-4501 X5384; Fax: 416-946-6566; Electronic mail: david.jaffray@rmp.uhn.on.ca


Abstract

The large variation of x-ray fluence at the detector in cone-beam CT (CBCT) poses a significant challenge to detectors’ limited dynamic range, resulting in the loss of skinline as well as reduction of CT number accuracy, contrast-to-noise ratio, and image uniformity. The authors investigate the performance of a bowtie filter implemented in a system for image-guided radiation therapy (Elekta oncology system, XVI) as a compensator for improved image quality through fluence modulation, reduction in x-ray scatter, and reduction in patient dose. Dose measurements with and without the bowtie filter were performed on a CTDI Dose phantom and an empirical fit was made to calculate dose for any radial distance from the central axis of the phantom. Regardless of patient size, shape, anatomical site, and field of view, the bowtie filter results in an overall improvement in CT number accuracy, image uniformity, low-contrast detectability, and imaging dose. The implemented bowtie filter offers a significant improvement in imaging performance and is compatible with the current clinical system for image-guided radiation therapy.

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