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Improving the Accuracy of 4DCT-Based Ventilation Measurements Using Multiple Phases

M Flakus1*, A Wuschner1 , E Wallat1 , W Shao2 , S Gerard2 , G Christensen2 , J Reinhardt2 , J Bayouth1 , (1) University of Wisconsin-Madison, Madison, WI, (2) University of Iowa, Iowa City, IA


(Tuesday, 7/16/2019) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 2

Purpose: To determine the effect of out of phase ventilation correction on the reproducibility of measuring the lung expansion ratio for the purpose of creating functional avoidance treatment plans.

Methods: In an IRB-approved trial to assess the potential benefit of functional avoidance radiation therapy for non-small cell lung cancer patients, subjects received two 4DCT scans using a respiratory gating system and audio guidance. The 4DCT scans were acquired 5 minutes apart prior to treatment. The image containing fewer artifacts was used for treatment planning, and the other scan was registered to the planning scan using a B-spline deformable image registration. The lung expansion ratio (LER) was computed and compared for two post-processing techniques, LER3D and LER4D. LER4D differs from LER3D by using data from all breathing phases to account for out of phase ventilation. The values for seven subjects with artifact free pre-RT scans were compared between LER3D and LER4D

Results: The variance of LER4D computed Jacobian ratios was found to be significantly less than that of LER3D (p<0.01). There is no significant difference in the means (p=0.5041). The volume of the lung in which there was a greater than 10% increase in LER between LER3D and LER4D was 239 cc avg. [range: 50.2 to 660].

Conclusion: The LER4D post-processing technique offers a more reproducible measure of LER than LER3D. LER4D eliminated the erroneous Jacobian values less than one and identifies regions of high functioning lung tissue that LER3D did not identify. The variance reduction with this technique demonstrates its improved reproducibility. The lung volume with corrected values is on the order of treatment target volumes. The clinical impact of these differences could be impactful if in regions receiving high radiation dose.


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