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Evaluation of a Correction Algorithm for Improving the Accuracy of a Deformable Image Registration Algorithm

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Y Mallya

Y Mallya1*, K Bzdusek2, (1) Philips Electronics India Pvt Ltd, Bangalore, Karnataka, (2) Philips Healthcare, Fitchburg, WI

SU-E-J-65 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To evaluate a correction algorithm for enhancing the accuracy of deformation vector field generated by deformable image registration(DIR) techniques.

Delineated contours of targets and organ at risk structures(OARs) in a pre-treatment prostate CT image volume were automatically propagated to the treatment CT image volume using an intensity based deformable image registration. All of the datasets used in this study were associated with expert-drawn contours for the structures in the treatment CT. The contours of the automatically propagated structures were corrected to match the corresponding expert-drawn contours of the structures in the treatment CT image. A modified Demons DIR algorithm was used to compute the incremental displacement vector field(DVF) that represented the corrections made to the automatically propagated contours. The initial DVF that was used for contour propagation was synchronized to the corrected contours by creating a composite vector field from the initial and the incremental DVF. The composite DVF was then used to propagate contours of targets and organ at risk structures from the planning CT to the treatment CT. Resulting deformed contours for each structure were compared to its corresponding expert-drawn contours using the Dice similarity coefficient(DSC) and Hausdorff distance(HD).

Visually the deformed contours using the corrected DVF were similar to the corrected and the expert-drawn contours. The Hausdorff distance improved up to 0.24mm from 1.33mm(82% improvement) and the DSC improved from up to 0.96 from 0.78(24% improvement).

The accuracy of the automatically propagated contours of targets and OARs using a corrected DVF were significantly higher than that obtained using the pre-corrected DVF. Therefore the technique can be used as an independent post processing step to correct the DVF generated by a DIR technique. The method could potentially be used to improve accuracy of subsequent dose deformation and accumulation steps of adaptive therapy.

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