Abstract
PurposeAs computed tomography (CT) imaging is the most commonly used modality for treatment planning in radiation therapy, metal artifacts in the planning CT images may complicate the target delineation and reduce the dose calculation accuracy. Although current CT scanners do provide certain correction steps, it is a common understanding that there is not a universal solution yet to the metal artifact reduction (MAR) in general. Particularly noting the importance of MAR for radiation treatment planning, we propose a novel MAR method in this work that recruits an additional tilted CT scan and synthesizes nearly metal‐artifact‐free CT images.MethodsThe proposed method is based on the facts that the most pronounced metal artifacts in CT images show up along the x‐ray beam direction traversing multiple metallic objects and that a tilted CT scan can provide complementary information free of such metal artifacts in the earlier scan. Although the tilted CT scan would contain its own metal artifacts in the images, the artifacts may manifest in a different fashion leaving a chance to concatenate the two CT images with the metal artifacts much suppressed. We developed an image processing technique that uses the structural similarity (SSIM) for suppressing the metal artifacts. On top of the additional scan, we proposed to use an existing MAR method for each scan if necessary to further suppress the metal artifacts.ResultsThe proposed method was validated by a simulation study using the pelvic region of an XCAT numerical phantom and also by an experimental study using the head part of the Rando phantom. The proposed method was found to effectively reduce the metal artifacts. Quantitative analyses revealed that the proposed method reduced the mean absolute percentages of the error by up to 86% and 89% in the simulation and experimental studies, respectively.ConclusionsIt was confirmed that the proposed method, using complementary information acquired from an additional tilted CT scan, can provide nearly metal‐artifact‐free images for the treatment planning.
Highlights
Metal artifacts in x‐ray computed tomography (CT) scans are due to the presence of high‐density objects, such as dental fillings, hip prostheses, and surgical clips, within the scanning field of view (FOV).[1–3] These artifacts are caused by multiple physical factors, including photon starvation, scatter, beam hardening, and noise
Using uncorrected CT images, Su et al demonstrated that intensity modulated radiation therapy (IMRT) treatment plans were superior to the conventional three‐ dimensional conformal radiation therapy (3D‐CRT) plans in delivering the planned dose and sparing the organs at risk (OARs) in an early stage prostate cancer patient with bilateral hip implants.[4]
Artifacts were still visible in the tilted CT scan, they were strongly reduced [Fig. 6(b)], indicating that the tilted CT scans, which avoided the overlap of metal implants along the beam direction, provide complementary information
Summary
Metal artifacts in x‐ray computed tomography (CT) scans are due to the presence of high‐density objects, such as dental fillings, hip prostheses, and surgical clips, within the scanning field of view (FOV).[1–3] These artifacts are caused by multiple physical factors, including photon starvation, scatter, beam hardening, and noise. Metal artifacts in x‐ray computed tomography (CT) scans are due to the presence of high‐density objects, such as dental fillings, hip prostheses, and surgical clips, within the scanning field of view (FOV).[1–3]. Reduced image quality prevents accurate delineation of structures, markedly reducing the diagnostic value of CT scans and the accuracy of dose calculations for radiation treatment planning. Unavoidable circumstances, such as the inclusion of metal implants in the treatment field, add up to the challenges of radiation therapy in delivering accurate dose to the tumor target while sparing the surrounding tissues. 6 MV four‐field RT plans were shown to be more susceptible to the metal artifacts than
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