SU-GG-T-593: Evaluation of Lung Dose Using Deformable 4DCT Registration Method

Abstract

Purpose: To evaluate the effect of breathing cycles on lungdose calculation using deformable 4DCT lung registration techniques. Method and Materials: A Philips Big Bore CT scanner was used to obtain CTimages for ten lungcancer patients. Both regular planning CTimages and 4D CTimages were obtained for each patient. With the planning CTimages,lung volume was segmented into different regions of interest, i.e. superior, middle, and inferior; mean doses of these ROIs were calculated from IMRT plans based on the same CTimages. 4D CTimages were divided into ten phases. Using deformable registration method, each phase of 4D CT data was registered with respect to the planning CTimages, and those ROIs were transformed into corresponding volumes associated with image sets of each 4D CT phase. The doses to the new transformed ROIs were calculated after applying the same IMRT beams generated from regular planning CT. Averaged over ten phases, the resulted mean lungdoses for ROIs were compared with those calculated from planning CTimages.Results: The lungdose calculation based on 4DCT images, taking into account of volume and density changes during the breathing cycle, results in a more accurate dose estimate. Without considering the lung movement presented in the 4DCT images, conventional lungdose calculation based on static planning CT could under‐estimates as much as 14.4% of mean dose compared with that obtained from 4D CT in lung regions experiencing larger breathing movement. It was found that exhale phases of breathing cycle could bring more lung mass into the radiation field, and thus contribute a higher mean dose to the lung.Conclusion: Deformable 4DCT lung registration can be used to calculate lungdose for radiation therapy. It provides more accurate dose estimates in lung regions with large breathing motion.