Metal artifact reduction through MVCBCT and kVCT in radiotherapy

Abstract

This study proposes a new method for removal of metal artifacts from megavoltage cone beam computed tomography (MVCBCT) and kilovoltage CT (kVCT) images. Both images were combined to obtain prior image, which was forward projected to obtain surrogate data and replace metal trace in the uncorrected kVCT image. The corrected image was then reconstructed through filtered back projection. A similar radiotherapy plan was designed using the theoretical CT image, the uncorrected kVCT image, and the corrected image. The corrected images removed most metal artifacts, and the CT values were accurate. The corrected image also distinguished the hollow circular hole at the center of the metal. The uncorrected kVCT image did not display the internal structure of the metal, and the hole was misclassified as metal portion. Dose distribution calculated based on the corrected image was similar to that based on the theoretical CT image. The calculated dose distribution also evidently differed between the uncorrected kVCT image and the theoretical CT image. The use of the combined kVCT and MVCBCT to obtain the prior image can distinctly improve the quality of CT images containing large metal implants.

The application of metal artifact reduction methods on computed tomography scans for radiotherapy applications: A literature review

“…These algorithms rely on several different principles. Some approaches are based on image inpainting or sinogram inpainting 72–75 ; some others require the acquisition of additional tilted CT scans, 76 propose novel image acquisition, and reconstruction methods 77,78 ; or require the use of magnetic resonance imaging (MRI) 79,80 or megavoltage CT (MVCT) 81,82 …”

“…Liugang et al proposed a MAR method which makes use of megavoltage computed tomography (MVCBCT) and kilovoltage computed tomography (kVCT) scans for MAR 81 . Initially, the metal part in the MVCBCT scan is segmented and forward projected to obtain the metal trace.…”

“…The density correction methods which are available in the TPSs can also be used to reduce the metal artifacts on CT scans for RT applications, see | 13 based on image inpainting or sinogram inpainting [72][73][74][75] ; some others require the acquisition of additional tilted CT scans, 76 propose novel image acquisition, and reconstruction methods 77,78 ; or require the use of magnetic resonance imaging (MRI) 79,80 or megavoltage CT (MVCT). 81,82 For the metal deletion technique (MDT) 75 (Fig. 4) which uses sinogram inpainting iteratively, initially pixels which contain metal data are segmented from CT art (Fig.…”

“…However, an evaluation of the absolute particle range difference on clinical CT cor showed that kerMAR significantly (P < 0.001) improved for electron beams nearly by 1 mm and proton beams by 2 mm in comparison with O-MAR. However, the photon beam evaluation showed an insignificant difference in depth/ range calculations on CT cor .In a MVCBCT-and kVCT-based MAR study,81 a custom-made phantom with a SS metal rod containing an air-filled hole in its center was CT scanned. The MAR method was applied to generate a CT cor from CT art .…”

Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on HalcyonTM for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses

“…The average-HUs for soft tissue equivalent inserts obtained with MV-CBCT did not depend on the presence or size of the metal implant (Figure 7E). Given the lack of metal artifacts and the ability to distinguish metal implants, MV-CBCT could be a convenient imaging method for planning quick turn-around cases in an emergency setting (16), or could be used to supplement a kVCT used for planning for patients with significant metal implants (17–20).…”