Healthc Inform Res.  2016 Oct;22(4):316-325. 10.4258/hir.2016.22.4.316.

Half-Fan-Based Intensity-Weighted Region-of-Interest Imaging for Low-Dose Cone-Beam CT in Image-Guided Radiation Therapy

• Yoo B
• Son K
• Pua R
• Kim J
• Solodov A
• Cho S

• KMID: 2357386
• DOI: http://doi.org/10.4258/hir.2016.22.4.316

Abstract

OBJECTIVES
With the increased use of computed tomography (CT) in clinics, dose reduction is the most important feature people seek when considering new CT techniques or applications. We developed an intensity-weighted region-of-interest (IWROI) imaging method in an exact half-fan geometry to reduce the imaging radiation dose to patients in cone-beam CT (CBCT) for image-guided radiation therapy (IGRT). While dose reduction is highly desirable, preserving the high-quality images of the ROI is also important for target localization in IGRT.
METHODS
An intensity-weighting (IW) filter made of copper was mounted in place of a bowtie filter on the X-ray tube unit of an on-board imager (OBI) system such that the filter can substantially reduce radiation exposure to the outer ROI. In addition to mounting the IW filter, the lead-blade collimation of the OBI was adjusted to produce an exact half-fan scanning geometry for a further reduction of the radiation dose. The chord-based rebinned backprojection-filtration (BPF) algorithm in circular CBCT was implemented for image reconstruction, and a humanoid pelvis phantom was used for the IWROI imaging experiment.
RESULTS
The IWROI image of the phantom was successfully reconstructed after beam-quality correction, and it was registered to the reference image within an acceptable level of tolerance. Dosimetric measurements revealed that the dose is reduced by approximately 61% in the inner ROI and by 73% in the outer ROI compared to the conventional bowtie filter-based half-fan scan.
CONCLUSIONS
The IWROI method substantially reduces the imaging radiation dose and provides reconstructed images with an acceptable level of quality for patient setup and target localization. The proposed half-fan-based IWROI imaging technique can add a valuable option to CBCT in IGRT applications.

Keyword

Cone-Beam Computed Tomography; Low-Dose; Region-of-Interest; Half-Fan; Image-Guided Radiation Therapy

MeSH Terms

Cone-Beam Computed Tomography*
Copper
Humans
Image Processing, Computer-Assisted
Methods
Pelvis
Radiation Exposure
Radiotherapy, Image-Guided*
Copper

Figure

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  Figure 1 Intensity-weighted region-of-interest (IWROI) imaging schematic in a conventional half-fan geometry. FOV: field-of-view.

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  Figure 2 Schematic of a rebinned half-fan geometry.

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  Figure 3 Images of (A) an on-board imager (OBI) system, (B) a mounted half-fan bowtie filter, (C) a humanoid phantom, and (D) a mounted intensity-weighting filter.

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  Figure 4 Log-transformed projection data (A) before and (B) after beam-quality correction. (C) Line profiles are shown for comparison. Note that the off-axis data are not shown.

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  Figure 5 (A) An open-field intensity map and (B) a raw projection of a phantom.

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  Figure 6 Film and glass dosimeters placed in the phantom for dosimetric measurements. XRCT: X-ray computed tomography.

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  Figure 7 Transverse images (A) before and (B) after; coronal images (C) before and (D) after; and sagittal images (E) before and (F) after beam-quality correction. The display window is [10, 250] HU for the images on the left and [10, 160] HU for the images on the right.

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  Figure 8 Line profiles of two images along the dashed line shown in Figure 7A. The solid line represents the uncorrected image and dashed line represents the corrected case.

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  Figure 9 Transverse slice of the target and moving images on a checkerboard: (A) before and (B) after image registration.

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  Figure 10 (A) Two-dimensional distribution of the imaging radiation dose (cGy) within the XRCT film for various experiments: no radiation or background (top), proposed method using a Cu filter (middle high), half-fan bowtie filter (middle low), and filter-free case (bottom). (B) Corresponding line profiles along the horizontal line near the bottom edge of the XRCT films are also shown. XRCT: X-ray computed tomography.

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