SU‐E‐J‐174: Volume Based Analysis of Several Doses Point and Their Relation to Changing Volume in a 4DCT

Abstract

Purpose:To evaluate several dose points in the low dose region of healthy lungs during XRT and their relationship to lung volume.Methods:10 lung cancer patients that had 4DCT simulations were selected for this study retrospectively. The lungs were countered in each of the 10 respiratory cycles. The clinical treatment plan was copied to each phase and the dose was recomputed. DVHs were tabulated for each phase and the V5, V20 and V30 dose points of the total lung, along with the volume of the lung for each phase was recorded. All these dose points and volumes were normalized to the free breathing scan and plan so as to establish if there was a trend, and what the nature of this trend was as a function of lung volume.Results:Of the first 4 patient analyzed, there was an established and reoccurring trend of the V5, V20, V30 dose normalized to the free breathing scan and plan. In the example of the two patients’ data(attached figure), normalized dose point and volumes are graphed as a function of the breathing phases. The precise variation of each point is not the same across each patient; however the trend of each variation seems predictive in nature. The next steps would be to run a statistical T‐test with all the patient data and see if there is a statistical significance and then try to establish a predictive model.Conclusion:Dose points for the lung such as V5, V20 and V30 are now better understood as toxicity end points for lung XRT. Although attention is paid to the low dose region of healthy lung tissue, this study shows that the volumetric affect on dose during breathing phases is measurable and could be statically significant. It therefore warrants further study to better understand this relationship.