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The Clinical Evaluation of a Minimum Point Distance Histogram for Image Registration in the 4DCT Based Gastric Cancer Radiotherapy


W Hu

W Hu1*, J Ye2, G Li1, Z Zhang1, (1) Fudan University Shanghai Cancer, Shanghai, Shanghai, (2) Swedish Medical Center-Tumor Institute, Seattle, WA

SU-E-J-75 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The contour-based evaluation is crucial in the radiotherapy and one popular parameter is the dice similarity coefficient (DSC). The DSC alone is insufficient in some situation and additional evaluation parameters are required. The purpose of this study is to create a minimum point distance histogram (mPDH) for contour-based deformable image registration evaluation and to investigate the clinical dosimetric endpoints related to the mPDH in organs at risk for gastric patients with 4DCT images.
Methods:The mPDH was created and tested in 4DCT images. The 0% phase (P0) and the 50% phase (P5) image data sets from 4DCT of 5 gastric cancer patients with contours delineated by a radiation oncologist were transferred to the VelocityVI image registration package. The contours on the P5 were rigidly transferred (rigid registration) and warped (deformable registration) to the P0. All contours were export to a homemade Matlab program for calculating the mPDH. The mPDHs were obtained for the rigid-manual (RM) and the deformed-manual (DM) contours. Furthermore, the original treatment plan was applied to the P0 for dose calculation and the dosimetry-based investigation related to the mPDH was performed.
Results:The mPDH provides a useful data for quantifying the agreement of the contours. The mean DI95%(the distance includes more than 95% of the points) and P3mm (the percent of points within 3mm distance) from mPDH show significant difference between the DM and RM (p<0.05). For dosimetric evaluation, there is no dose check point has difference larger than 3% if the DI95% is within 4mm.
Conclusion:A new informative image registration evaluation tool is created. The mPDH provides a useful data for quantifying the agreement of the contours. The clinical validation of mPDH in the gastric cancer shows the feasibility of apply this tool in the radiotherapy for evaluation the clinical accuracy of deformable registration.

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