Patient dose and image quality from mega-voltage cone beam computed tomography imaging
The cylindrical acrylic phantoms measurement setup. A small volume chamber was placed at the isocenter as well as below the surface at the 0°, 90°, 180°, and 270° positions.
The TLD measurement setup in a Rando phantom: (a) pelvic region and (b) head and neck region. Each TLD is located from its closest neighbor. The circles mark the TLD locations. The beam arc rotates from 270° to 110°.
Schematic of (a) the contrast section of the image quality phantom, containing four sets of inserts of different electron density with respect to water: air and materials with density of 1.09, 1.17, and 1.48, respectively; (b) the spatial resolution section of the image quality phantom, containing 11 groups of bars whose spacings correspond to different resolutions.
Dose delivered at the isocenter by the 8, 10 and protocols in the pelvic phantom, and by the 5, 8 and protocols in the head and neck phantom. Data were fitted with a linear function that included the origin at 0.
Isodose lines in the pelvic and the head and neck Rando phantoms for the and protocols, respectively; (a,d) superior to the isocenter plane, (b,e) isocenter plane, (c,f) inferior to the isocenter plane. The position of the isocenter axis is located at the crossing of the dark horizontal and vertical lines.
The reconstructed image of a slice in the low contrast section of the image quality phantom by a CT scanner (kV-CT, top left) and MV-CBCT system for seven different MU protocols (3, 5, 8, 10, 12, 15, and ) identified by their calculated isocenter dose.
Contrast to noise ratio (CNR) measured for seven different MU protocols (3, 5, 8, 10, 12, 15, and ) as a function of the dose delivered at the insert location. Each curve is identified by the electron density of the material relative to the background. The CNR varies as the square root of the dose.
Transverse slice of a head and neck patient imaged with (a) kV-CT, (b) MV-CBCT protocol, (c) MV-CBCT protocol. The lower dose is sufficient to show the bony structures on the MV-CBCT image. Soft tissue boundaries are more visible with the higher dose.
Dose delivered to the acrylic phantoms measured using a small volume ion chamber, along with the XiO treatment planning system (TPS) calculations.
TLD dose measurements in the pelvic Rando phantom for the protocol, along with the XiO treatment planning system calculations. The measured dose value is the average of the three TLD measurements in the same horizontal plane.
TLD dose measurements in the nasopharynx of the Rando phantom for the protocol, along with the XiO treatment planning system calculations. The measured dose value is the average of the three TLD measurements in the same horizontal plane.
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