As computed tomography (CT) imaging is the most commonly used modality for treatment planning in radiation therapy, metal artifacts in planning CT images may complicate the target delineation and reduce the dose accuracy.

Although current CT scanners do not provide certain correction steps, it is a common understanding that there is a universal solution 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 CT CT scan and synthesizes nearly metal-artifact-free CT images.

Tilted CT scan

The proposed method is based on the facts that most accurate metal artifacts in CT images show up along the x-ray beam direction traversing multiple metallic objects and that a CT CT scan can provide complementary information free of such metal artifacts in the earlier scan.

Although the 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.

The researchers developed an image processing technique that uses the structural similarity (SSIM) for suppressing the metal artifacts. On top of the additional scan, they proposed to use an existing MAR method for each scan if necessary to further suppress the metal artifacts.

The 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 analyzes 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.

It was confirmed that the proposed method, using complementary information acquired from an additional CT CT scan, can provide nearly metal-artifact-free images for the treatment planning.