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Quantitative Investigation of Image Artifact in CT Images of a Multiple Diode Array Detector and Their Effects On the Dose Distributions Calculated with AAA and Acuros-XB Algorithms

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I Ali

F Almatouq, S Ahmad , O Algan , I Ali , Oklahoma Univ. Health Science Ctr., Oklahoma City, OK


WE-RAM3-GePD-JT-1 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Theater

Purpose: To investigate quantitatively the variations in CT numbers due to image artifacts in CT images of a multiple-array-diode detector (Mapcheck2) and their effects on dose distributions calculated by the anisotropic-analytical-algorithm (AAA) and Acuros-XB dose calculation algorithms.

Methods: The dose distributions from 25 treatment plans for different site generated with the Eclipse treatment planning system were mapped to a multiple-diode-array-detector. The dose distributions were calculated using two dose calculation algorithms: AAA and Acuros-XB with heterogeneity on/off using the CT-numbers from the helical CT images of MapCheck2. Same optimized-fluence maps were used for dose calculations with the previous algorithms. The calculated dose distributions were compared to measured distributions with MapCheck2.

Results: The mean value of the CT-numbers of the MapCheck2 varied from 170 HU in the solid-water-phantom to 2900 HU near the layer that included the diodes because of image artifacts. The CT-numbers varied over a wide range of -970 HU in air to 3000 HU in metal. The dose distributions calculated with AAA with heterogeneity correction agreed well with the measured dose distributions and passed the gamma test (95%,3%,3mm). The dose distribution calculated with Acuros-XB considering heterogeneity correction of the CT numbers of MapCheck2 were 8% higher on average than the corresponding dose distribution calculated with AAA. The dose deviations between Acuros-XB and AAA ranged from 0-20% due mainly to image artifacts. The Acuros-XB dose distributions did not pass gamma test.

Conclusion: The dose distributions calculated with the Acuros-XB were systematically higher than the corresponding dose distributions calculated by AAA and measured distributions due to image artifacts in the CT-images of the multiple-diode-array detectors. In order to use the MapCheck2 for the verification of the dose distributions calculated by Acuors, the CT-number values have to be corrected from image artifacts.

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