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Assessing Variation in Local Lung Function Prior To, During and Following Radiation Therapy

M Flakus1*, E Wallat2, W Shao3, A Wuschner4, G Christensen5, J Reinhardt6, D Shanmuganayagam7, J Bayouth8, (1) ,Madison, WI, (2) ,Verona, WI, (3) ,Iowa City, ,(4) ,Madison, WI, (5) Univ Iowa, Iowa City, IA, (6) The University of Iowa, Iowa City, IA, (7) ,Madison, WI, (8) University of Wisconsin, Madison, WI


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To quantify the repeatability of lung tissue elasticity measures for the purpose of creating functional avoidance treatment plans and assessing local response to radiation.

Methods: In an IRB-approved clinical trial, 71 human subjects presenting lung cancer underwent radiation therapy (RT), in which they received two four-dimensional-computed-tomography (4DCT) scans prior to and three months following RT. Additionally, four Wisconsin Minature SwineTM (WMS) underwent an IACUC-approved 5 fraction RT treatment of 12 Gy per fraction. The WMS subjects received three 4DCTs prior to each fraction while mechanically ventilated. In both studies, Jacobian based 4DCT-derived ventilation maps were created to compare variation in local lung function between repeat scans, across days of treatment and following therapy. The effect of RT on lung function was quantified by comparing voxels receiving more than 5-10 Gy per fraction to untreated regions. Gamma analysis was used to assess repeatability in both groups.

Results: For repeat scans acquired on the same day, WMS subjects had an average gamma pass rate of 85% [range: 41% to 96%] while human subjects averaged 70% [range: 34% to 89%]. Between each fraction for WMS, the gamma pass rate was 74% in unirradiated lung, with a significant decrease for voxels receiving more than 5 Gy (65%, p<.001) and 10 Gy (54%, p<.001). In comparing post-RT lung function to pre-RT, the WMS and clinical trial subjects had gamma pass rates of 60% and 56% respectively.

Conclusion: WMS subjects provided a more repeatable dataset than human subjects, which can be used to assess the lower limits of uncertainty. Quantifying and reducing these uncertainties allow for a more precise assessment of lung function change following therapy. Inter-fraction dose dependent WMS data suggests these measures can demonstrate increased sensitivity in a controlled setting.


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