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A Comparison of Noninvasive Techniques to Assess Radiation-Induced Lung Damage in Mice

A Rubinstein

A Rubinstein*, C Kingsley, A Melancon, R Tailor, J Pollard, M Guindani, D Followill, J Hazle, L Court, The University of Texas MD Anderson Cancer Center, Houston, TX


TU-H-CAMPUS-TeP2-1 (Tuesday, August 2, 2016) 5:00 PM - 5:30 PM Room: ePoster Theater

Purpose:To evaluate the use of post-irradiation changes in respiratory rate and CBCT-based morphology as predictors of survival in mice.

Methods:C57L/J mice underwent whole-thorax irradiation with a Co-60 beam to four different doses [0Gy (n=3), 9Gy (n=5), 11Gy (n=7), and 13Gy (n=5)] in order to induce varying levels of pneumonitis. Respiratory rate measurements, breath-hold CBCTs, and free-breathing CBCTs were acquired pre-irradiation and at six time points between two and seven months post-irradiation. For respiratory rate measurements, we developed a novel computer-vision-based technique. We recorded mice sleeping in standard laboratory cages with a 30 fps, 1080p webcam (Logitech C920). We calculated respiratory rate using corner detection and optical flow to track cyclical motion in the fur in the recorded video. Breath-hold and free-breathing CBCTs were acquired on the X-RAD225Cx system. For breath-hold imaging, the mice were intubated and their breath was held at full-inhale for 20 seconds. Healthy lung tissue was delineated in the scans using auto-threshold contouring (0-0.7 g/cm³). The volume of healthy lung was measured in each of the scans. Next, lung density was measured in a 6-mm² ROI in a fixed anatomic location in each of the scans.

Results:Day-to-day variability in respiratory rate with our technique was 13%. All metrics except for breath-hold lung volume were correlated with survival: lung density on free-breathing (r=-0.7482,p<0.01) and breath-hold images (r=-0.5864,p<0.01), free-breathing lung volume (r=0.7179,p<0.01), and respiratory rate (r= 0.6953,p<0.01). Lung density on free-breathing scans was correlated with respiratory rate (r=0.7142,p<0.01) and lung density on breath-hold scans (r=0.5543,p<0.01). One significant practical hurdle in the CBCT measurements was that at least one lobe of the lung was collapsed in 36% of free-breathing scans and 45% of breath-hold scans.

Conclusion:Lung density and lung volume on free-breathing CBCTs and respiratory rate outperform breath-hold CBCT measurements as indicators for survival from radiation-induced pneumonitis.

Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by Elekta.

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