Abstract
We aimed to clarify the accuracy of rigid image registration and deformable image registration (DIR) in carbon-ion radiotherapy (CIRT) for pancreatic cancer. Six patients with pancreatic cancer who were treated with passive irradiation CIRT were enrolled. Three registration patterns were evaluated: treatment planning computed tomography images (TPCT) to CT images acquired in the treatment room (IRCT) in the supine position, TPCT to IRCT in the prone position, and TPCT in the supine position to the prone position. After warping the contours of the original CT images to the destination CT images using deformation matrices from the registration, the warped delineated contours on the destination CT images were compared with the original ones using mean displacement to agreement (MDA). Four contours (clinical target volume (CTV), gross tumor volume (GTV), stomach, duodenum) and four registration algorithms (rigid image registration [RIR], intensity-based DIR [iDIR], contour-based DIR [cDIR], and a hybrid iDIR-cDIR ([hDIR]) were evaluated. The means ± standard deviation of the MDAs of all contours for RIR, iDIR, cDIR, and hDIR were 3.40 ± 3.30, 2.2 1± 2.48, 1.46 ± 1.49, and 1.46 ± 1.37 mm, respectively. There were significant differences between RIR and iDIR, and between RIR/iDIR and cDIR/hDIR. For the pancreatic cancer patient images, cDIR and hDIR had better accuracy than RIR and iDIR.
Highlights
As carbon-ion beams have the characteristics of a Bragg peak and sharper penumbra [1], they can generate a more conformal dose distribution than X-ray beams [2]
We assume that intensity-based deformable image registration (iDIR) is effective when deformations are small and the boundary of the contour is clear
Because contour-based DIR (cDIR) and hybrid intensity- and contour-based deformable image registration (hDIR) are less affected by the above effects, they were better than iDIR for the CTV, stomach, and duodenum
Summary
As carbon-ion beams have the characteristics of a Bragg peak and sharper penumbra [1], they can generate a more conformal dose distribution than X-ray beams [2]. It was reported that changes were observed for mobile organs that moved with respiratory movement [3,4,5,6,7,8]. To safely treat such organs, it is necessary to confirm the reproducibility of the dose distributions. Confirming the dose distributions during the whole treatment days can obtain a more accurate estimation for the irradiated dose, and it is effective for predicting treatment outcomes and toxicities [9]. It is necessary to acquire computed tomography (CT) images on whole treatment days, to calculate the dose distributions on the CT images, and to accumulate the overall dose distributions [7,9,10]
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