(Saturday, 4/4/2020) 10:30 AM - 12:30 PM [Mountain Time (GMT-6)]
Purpose: To measure post-RT changes in regional pulmonary vasculature and develop a dose response model to aid in functional avoidance radiation therapy treatment planning.
Methods: A cohort of 37 subjects were recruited for an IRB approved clinical trial analyzing pulmonary function post-RT. Each subject received a CT scan prior to and 3 months following 60Gy delivered in either 5 or 30 fractions of RT. Voxels containing lung vessels were identified on the CTs using a filtration probability map (Frangi Vesselness). The volume of vasculature in the lung was calculated before and post-RT by integrating this map. Analysis was discretized into 10Gy dose bins to analyze dose response and results were stratified into two subject pools; patients receiving hypo-fractionated therapy (n=18) and standard fractionation therapy (n=19).
Results: Statistically significant (p<0.05) reductions (7.7%) in vasculature were observed in the standard fractionation group over the entire lung. In the hypo-fractionated group, no significant changes were observed. A linearly increasing (r²=0.9974) percent reduction with increasing dose was observed up to the 25-35Gy dose bin. Percent reductions were 4.8%, 15%, and 23.6% in the 5-15Gy, 15-25Gy, and 25-35Gy bins respectively. At higher dose levels, damage was difficult to interpret. Percent reduction decreased to 21.6% in the 35-45Gy bin. Above 45Gy no significant difference was observed. Vasculature irradiated greater than 15Gy saw an average reduction of 16% which was statistically significant compared to the regions irradiated with 5-15Gy which only saw a 4.8% reduction (p=0.014).
Conclusion: This work indicates a radiation induced change in the pulmonary vasculature that increases in severity with increasing dose. We speculate the change in behavior is due to the onset of fibrosis being falsely labeled as vasculature and thus skewing the comparison between pre and post RT scans. Future work is required to fully understand the results at higher dose levels.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Institutes of Health grant CA166703
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