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Proceedings Paper

Quantitative investigations of megavoltage computed tomography
Author(s): Myron Rogers; Andrew Kerr; Greg Salomons; L. John Schreiner
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Paper Abstract

Megavoltage computed tomography (MVCT) has been an active area of research and development in image guided radiation therapy. We have been investigating a particular implementation of MVCT in conjunction with studies of the potential for tomotherapy with a Cobalt-60 radiation source. In this paper, we present results comparing MVCT using a Co-60 source and a 4 MV linear accelerator to conventional kVCT imaging. The Co-60 and linac MVCT measurements were obtained with a first generation benchtop CT imager; the KVCT measurements were obtained using a Philips AcQSim CT Simulator). Phantoms containing various inserts ranging in density from air, through lung, soft tissue and bone equivalent materials and extending to high atomic number metals were imaged with the three modalities. The results enable characterization of image artifacts, CT number linearity and beam hardening. The MVCT images have sufficient contrast that soft tissue regions with 2.8% difference in electron density can be visualized. In MVCT, a linear relationship between CT numbers and electron densities extends to materials with Z ≈ 60. In the 4MV CT imaging there is a position dependence of the CT numbers within a uniform water phantom, which is absent in Co-60 CT images, indicating the presence of beam hardening artifacts in the linac MVCT images. The differences between kVCT and MVCT will be discussed considering the variation of the photon interactions dominating the images. Our investigations indicate that MVCT has properties that may potentially extend its utility beyond radiation therapy.

Paper Details

Date Published: 20 April 2005
PDF: 10 pages
Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); doi: 10.1117/12.596047
Show Author Affiliations
Myron Rogers, Cancer Ctr. of Southeastern Ontario (Canada)
Andrew Kerr, Cancer Ctr. of Southeastern Ontario (Canada)
Queen's Univ. (Canada)
Greg Salomons, Cancer Ctr. of Southeastern Ontario (Canada)
Queen's Univ. (Canada)
L. John Schreiner, Cancer Ctr. of Southeastern Ontario (Canada)
Queen's Univ. (Canada)

Published in SPIE Proceedings Vol. 5745:
Medical Imaging 2005: Physics of Medical Imaging
Michael J. Flynn, Editor(s)

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