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Propagation of Pancreas Target Contours On Respiratory Correlated CT Images Using Deformable Image Registration
F Liu1*, E Yorke2 , G Mageras2 , K Goodman2 , (1) Rhode Island Hospital / Brown University, Providence, RI, (2) Memorial Sloan-Kettering Cancer Center, New York, NY
Presentations
SU-E-J-226 Sunday 3:00PM - 6:00PM Room: Exhibit HallPurpose:Respiratory Correlated CT (RCCT) scans to assess intra-fraction motion among pancreatic cancer patients undergoing radiotherapy allow for dose sparing of normal tissues, in particular for the duodenum. Contour propagation of the gross tumor volume (GTV) from one reference respiratory phase to 9 other phases is time consuming. Deformable image registration (DIR) has been successfully used for high contrast disease sites but lower contrast for pancreatic tumors may compromise accuracy. This study evaluates the accuracy of Fast Free Form (FFF) registration-based contour propagation of the GTV on RCCT scans of pancreas cancer patients.
Methods:Twenty-four pancreatic cancer patients were retrospectively studied; 20 had tumors in the pancreatic head/neck, 4 in the body/tail. Patients were simulated with RCCT and images were sorted into 10 respiratory phases. A radiation oncologist manually delineated the GTV for 5 phases (0%, 30%, 50%, 70% and 90%). The FFF algorithm was used to map deformations between the EE (50%) phase and each of the other 4 phases. The resultant deformation fields served to propagate GTV contours from EE to the other phases. The Dice Similarity Coefficient (DSC), which measures agreement between the DIR-propagated and manually-delineated GTVs, was used to quantitatively examine DIR accuracy.
Results:Average DSC over all scans and patients is 0.82 and standard deviation is 0.09 (DSC range 0.97 -0.57). For GTV volumes above and below the median volume of 20.2 cc, a Wilcoxon rank-sum test shows significantly different DSC (p=0.0000002). For the GTVs above the median volume, average +/- SD is 0.85 +/- 0.07; and for the GTVs below, the average +/- SD is 0.75 +/- 0.08.
Conclusion:For pancreatic tumors, the FFF DIR algorithm accurately propagated the GTV between the images in different phases of RCCT, with improved performance for larger tumors.
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