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Longitudinal Changes in Lung Tissue Elasticity Following Radiation Therapy

J Bayouth1*, E Wallat2 , A Wuschner3 , M Flakus4 , T Patton5 , W Shao6 , S Gerard7 , J Reinhardt8 , G Christensen9 , A Baschnagel10 , (1) University of Wisconsin, Madison, WI, (2) ,Verona, WI, (3) ,Madison, WI, (4) ,Madison, WI, (5) ,Denver, CO, (6) ,Iowa City, ,(7) ,Iowa City, ,(8) The University of Iowa, Iowa City, IA, (9) Univ Iowa, Iowa City, IA, (10) ,Madison,


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

Room: Exhibit Hall | Forum 2

Purpose: Ventilation is estimated using deformable image registration applied to 4D computed tomography (4DCT) datasets. We investigate whether scans at 3 or 6 months after radiation therapy (RT) showed greater ventilation response to dose.

Methods: Twenty-seven patients had 4DCT datasets acquired at 3 time points: before RT, 3 months post-RT, and 6 months post-RT. Each patient received 60 Gy in either 5 or 30 fractions as part of an institutionally approved IRB prospective clinical trial. For each dataset, ventilation was estimated using the Jacobian determinant of the transformation given by deformable image registration of the 4DCT dataset. The post-RT maps were deformed to the pre-RT map and a voxel-wise ratio of each post-RT map to the pre-RT map was taken to determine the ventilation response at 3 and 6 months post-RT. Endpoints for comparison were the percent of lung that expands less than 94% of baseline (damaged), percent of lung that expands more than 106% of baseline (improved), and the amount of lung with > 10% expansion (high functioning).

Results: In all subjects lung tissue elasticity was reduced following RT, regardless of fractionation scheme. The amount of damaged lung (25% to 29%, p=0.049), improved lung (21% vs 19%) and high functioning lung (67% vs 66 %) were more pronounced when considering 3 mo vs 6 mo post-RT. Also, the amount of damaged lung was significantly greater than improved at 6 mo post-RT (p=0.033), but only trending different at 3 mo post-RT (p=0.14).

Conclusion: CT based lung ventilation data 6 months post-RT showed increased change compared to 3 months post-RT. Correlation of these imaging biomarker changes with clinical metrics are required. Researchers should use 6 month follow up imaging when possible, as 3 month follow up will require a larger sample size to show significance.


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