Soft Tissue Visualization Using a Highly Efficient Megavoltage Cone ...

3.2.2 Patient Images
Figure 6: Receptor 1Head phantom images with gold seeds
All patient images were acquired at SID of 145cm. Figure 7 shows a pelvis image acquired with
receptor 1. Total dose was 16cGy and preprocessing adaptive filter was applied to the projection
images. The contribution of beam profile and scatter effects that cause shading artefacts are minimized
by obtaining empirical data (from different anatomies, SID, and patient sizes) and linking to the
correction images. Figure 8 compares the axial view of 8cGy MV CBCT with the planning CT image
and shows that the most of the soft tissue structures such as prostate are detectable with MV CBCT.
Figures 9 and 10 depict axial, coronal and sagittal head/neck images that were acquired with receptors
1 and 2 by delivering 16 and 6cGy, respectively. Optic nerves are detectable in both figures. Figure 11
compares the lateral views of MV CBCT images acquired for three different patients over the past year
and shows the improvement in image quality.
One distinct advantage of MV CBCT imaging is that image quality is maintained even when high-Z
materials such as tooth fillings, dental implants, fiducial markers or hip replacements are present. For
kV imaging, these objects create strong artifacts. This is illustrated in the figure 12.
Figure 7: Pelvis MV CBCT with receptor 1 using 16cGy