(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To evaluate quantitatively dosimetric uncertainties associated with the MapCheck2 used for intensity-modulated radiation therapy quality assurance of dose distributions calculated with Acuros-XB and anisotropic-analytical-algorithm (AAA) dose calculation algorithms in the Eclipse treatment planning system.
Methods: MapCheck2 is made from multiple-diode-array detector which was used to measure the dose distributions from 25 treatment plans for different site generated with the Eclipse treatment planning system. The treatment plans were mapped to the MapCheck2 phantom and calculated using the AAA and Acuros-XB with heterogeneity on/off using the CT-numbers from the helical CT images and compared with the corresponding measured dose distributions with MapCheck2.
Results: The CT-images of the MapCheck2 phantom have significant artifacts induced by the diodes where the CT-numbers varied over a wide range of -970 to 3000 HU. The mean value of the CT-numbers of MapCheck2 varied from 50 HU in upper layers of the solid-water phantom to 1400 HU in the phantom layer that includes the diode-array detector. The corresponding dose distributions calculated with Acuros-XB considering heterogeneity correction of the CT-images of the MapCheck2 with image artifacts varied by 8% from the corresponding upper phantom layer at the level of the diodes relative to the doses calculated at the water-equivalent phantom of MapCheck2. While the dose distributions calculated with AAA agreed with the measured dose distributions because it is not very sensitive to variations in the CT-number values induced by metal artifacts. One approach to verify the dose distribution calculated by Acuros-XB with MapCheck2 is to override the corrupted CT-numbers to solid water values in phantom layers above and below the diodes-array.
Conclusion: Image artifacts induced large uncertainties in the CT-numbers which led to large discrepancies between the doses measured by MapCheck2 and calculated Acuros-XB which can be corrected by overriding the CT number values corrupted by image artifacts.
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