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Spatial and Dose-Response Analysis of Fibrotic Lung Changes After Stereotactic Body Radiation Therapy

Y Vinogradskiy*, Q Diot, B Kavanagh, L Gaspar, M Miften, University of Colorado School of Medicine, Aurora, CO

TH-C-213AB-1 Thursday 10:30:00 AM - 12:30:00 PM Room: 213AB

Purpose: To evaluate fibrotic lung changes in patients that underwent stereotactic body radiation therapy (SBRT) for lung cancer. Specifically, we contoured volumes visually observed to have fibrotic CT changes, performed a dose-response analysis, and studied the spatial location and movement of the fibrotic volumes.

Methods: Our study cohort included 51 SBRT patients and 231 follow up CT scans. The follow up CT scans were binned into intervals of 3, 6, 12, 18, 24, 30, 36, 42, and 48 months post therapy. Areas of visible fibrotic changes were contoured on follow up CTs. Deformable registration was used to align each follow up CT to the pre-treatment CT scan. Spatial analysis was performed by determining the centroid of the gross tumor volume (GTV) and each fibrosis volume and analyzing the location and motion of the fibrosis volume relative to the GTV. A dose-response analysis was performed by binning each voxel in the fibrosis volume into 10Gy dose-bins and analyzing the CT numbers in each dose-bin with respect to dose and time after treatment.

Results: The distribution of fibrosis volumes was 51%, 39%, and 10% in the superior, middle, and inferior regions of the lung respectively. The average radial travel between the fibrosis volume centroid and GTV centroid was 2.6±0.2cm. The volume of the fibrosis region was greatest at 3 months (47cc) and decreased over time to 18cc at 46 months. Dose-response data revealed increasing CT numbers as a function of dose (with no decline at higher doses) and increasing CT number as a function of time.

Conclusions: The highest concentration of fibrosis volumes was located in the upper third of the lung. Future work will explore the relationship between fibrosis location, fibrosis volume, and dose. Our results show consolidation of the fibrotic volume and increase of CT number with dose and time.

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