High-dose MVCT image guidance for stereotactic body radiation therapy
(a) Customized Siemens image quality phantom used to assess image quality of the standard, medium, and high-dose MVCT imaging modes. Shown are kVCT scans of the (b) contrast resolution module containing inserts of varying electron density materials, (c) spatial resolution module embedded with bar patterns of varying spatial frequencies, and (d) uniformity module composed of homogeneous solid water.
Weighted CT dose index values computed from phantom dose measurements made for the standard, medium, and high-dose imaging modes vs helical pitch. Pitch values correspond to the fine, normal, and coarse scan settings in the TomoTherapy operator station software.
MVCT scans of the three image quality modules considered in this work acquired using the standard, medium, and high-dose imaging modes. From top row to bottom are shown the contrast resolution, spatial resolution, and image uniformity modules. The most notable improvement in image quality is a reduction in image noise seen with increasing imaging dose. In addition, the central noise artifact seen in all images is reduced with the higher dose modes.
Average contrast-to-noise ratios computed for each electron density (ED) material insert on five slices of the contrast resolution module images acquired using the standard, medium, and high-dose imaging modes. Error bars indicate one standard deviation. Dashed lines represent square root power law fits to the data and indicate that for all materials, the CNR increases as the square root of the imaging dose.
Average modulation transfer function (MTF) values computed for the different spatial frequency bar patterns on five slices of the spatial resolution module images acquired using the standard, medium, and high-dose imaging modes. Error bars indicate one standard deviation. MTF values were similar for all imaging modes with a limiting resolution (corresponding to a cutoff MTF value of 0.1) of 0.5 lp/mm.
Localization image acquired for a representative liver SBRT patient using the high-dose imaging mode and normal scan setting. Raw detector data exported from the system were sampled, allowing for a standard-dose image of the same patient anatomy to be reconstructed. The high-dose image is characterized by an overall reduction in image noise compared to the standard-dose image, making it easier to distinguish boundaries between different soft tissues.
Dose measurements made using the fine scan setting (pitch = 1.0).
Image uniformity and percent noise data.
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