Room: Exhibi Hall | Forum 6
Purpose: To evaluate quantitatively image artifacts induced by metal in CT-images acquired with different photon energies 80-140kV and to determine optimal kV energy that provides CT imaging with the least metal artifacts. The deviations in the calculated doses for treatment plan verifications and dosimeteric quality assurance associated with the CT-number variations induced by metal artifacts and their dependence on the beam energy of the CT-images were evaluated.
Methods: The MapCheck2-phantom was scanned with a GE-Discovery scanner with multiple photon energies including 80, 100, 120 and 140 kV. This phantom includes a multiple-diode-array-detectors made form high-z material. The imaging parameters were kept the same except the energy of the photon beam. Different treatment plans were mapped to the CT-images of the MapCheck2 used for dose verification and quality assurance. The dose distributions were calculated with Eclipse treatment planning system using different dose calculation algorithms.
Results: The high-z diodes induced strong image artifacts in CT-images particularly in the layer that included the diode-array and the close phantom layers where the CT numbers varied from -1000 to 3000HU. These artifacts decreased in the phantom layers that are far from the diodes. The CT-images acquired with lowest energy (80kV) showed the strongest metal artifacts and largest variations in CT-number values. The variations of the CT-numbers induced by metal artifact decreased with increasing energy. The dose deviations increased with increasing variations in the CT-numbers with largest deviations using CT-images acquired with 80kV energy.
Conclusion: Metal artifacts were the strongest in the CT-images acquired with the lowest 80kV energy. The variations in the CT-numbers with lower imaging photon energy led to large discrepancies in the dose calculation algorithms that are sensitive to variations in the CT-numbers. Using imaging beams with high photon energy decreased the image artifacts and decreased discrepancy in the calculated dose on MapCheck2-phantom.
Not Applicable / None Entered.