Deep Learning–Based CT-to-CBCT Deformable Image Registration for Autosegmentation in Head and Neck Adaptive Radiation Therapy

Abstract

The purpose of this study is to develop a deep learning–based method that can automatically generate segmentations on conebeam computed tomography (CBCT) for head and neck online adaptive radiation therapy (ART), where expert-drawn contours in planning CT (pCT) images serve as prior knowledge. Because of the many artifacts and truncations that characterize CBCT, we propose to utilize a learning-based deformable image registration method and contour propagation to get updated contours on CBCT. Our method takes CBCT and pCT as inputs, and it outputs a deformation vector field and synthetic CT (sCT) simultaneously by jointly training a CycleGAN model and 5-cascaded Voxelmorph model. The CycleGAN generates the sCT from CBCT, while the 5-cascaded Voxelmorph warps the pCT to the sCT’s anatomy. We compared the segmentation results to Elastix, Voxelmorph and 5-cascaded Voxelmorph models on 18 structures including target and organs-at-risk. Our proposed method achieved an average Dice similarity coefficient of 0.83 ± 0.09 and an average 95% Hausdorff distance of 2.01 ± 1.81 mm. Our method showed better accuracy than Voxelmorph and 5-cascaded Voxelmorph and comparable accuracy to Elastix, but with much higher efficiency. The proposed method can rapidly and simultaneously generate sCT with correct CT numbers and propagate contours from pCT to CBCT for online ART replanning.