Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2014 Mar;41(3):031908.
doi: 10.1118/1.4865788.

Investigation into image quality and dose for different patient geometries with multiple cone-beam CT systems

Stephen J Gardner  1 , Matthew T Studenski  2 , Tawfik Giaddui  3 , Yunfeng Cui  4 , James Galvin  3 , Yan Yu  3 , Ying Xiao  3
Affiliations

Investigation into image quality and dose for different patient geometries with multiple cone-beam CT systems

Stephen J Gardner et al. Med Phys. 2014 Mar.

Abstract

Purpose: To provide quantitative and qualitative image quality metrics and imaging dose for modern Varian On-board Imager (OBI) (ver. 1.5) and Elekta X-ray Volume Imager (XVI) (ver. 4.5R) cone-beam computed tomography (CBCT) systems in a clinical adaptive radiation therapy environment by accounting for varying patient thickness.

Methods: Image quality measurements were acquired with Catphan 504 phantom (nominal diameter and with additional 10 cm thickness) for OBI and XVI systems and compared to planning CT (pCT) (GE LightSpeed). Various clinical protocols were analyzed for the OBI and XVI systems and analyzed using image quality metrics, including spatial resolution, low contrast detectability, uniformity, and HU sensitivity. Imaging dose measurements were acquired in Wellhofer Scanditronix i'mRT phantom at nominal phantom diameter and with additional 4 cm phantom diameter using GafChromic XRQA2 film. Calibration curves were generated using previously published in-air Air Kerma calibration method.

Results: The OBI system full trajectory scans exhibited very little dependence on phantom thickness for accurate HU calculation, while half-trajectory scans with full-fan filter exhibited dependence of HU calculation on phantom thickness. The contrast-to-noise ratio (CNR) for the OBI scans decreased with additional phantom thickness. The uniformity of Head protocol scan was most significantly affected with additional phantom thickness. The spatial resolution and CNR compared favorably with pCT, while the uniformity of the OBI system was slightly inferior to pCT. The OBI scan protocol dose levels for nominal phantom thickness at the central portion of the phantom were 2.61, 0.72, and 1.88 cGy, and for additional phantom thickness were 1.95, 0.48, and 1.52 cGy, for the Pelvis, Thorax, and Spotlight protocols, respectively. The XVI system scans exhibited dependence on phantom thickness for accurate HU calculation regardless of trajectory. The CNR for the XVI scans decreased with additional phantom thickness. The uniformity of the XVI scans was significantly dependent on the selection of the proper FOV setting for all phantom geometries. The spatial resolution, CNR, and uniformity for XVI were lower than values measured for pCT. The XVI scan protocol dose levels at the central portion of the phantom for nominal phantom thickness were 2.14, 2.15, and 0.33 cGy, and for additional phantom thickness were 1.56, 1.68, and 0.21 cGy, for the Pelvis M20, Chest M20, and Prostate Seed S10 scan protocols, respectively.

Conclusions: The OBI system offered comparable spatial resolution and CNR results to the results for pCT. Full trajectory scans with the OBI system need little-to-no correction for HU calculation based on HU stability with changing phantom thickness. The XVI system offered lower spatial resolution and CNR results than pCT. In addition, the HU calculation for all scan protocols was dependent on the phantom thickness. The uniformity for each CBCT system was inferior to that of pCT for each phantom geometry. The dose for each system and scan protocol in the interior of the phantom tended to decrease by approximately 25% with 4 cm additional phantom thickness.

PubMed Disclaimer

Figures

FIG. 1.
FIG. 1.
(a) and (b) Cross-section images of the Catphan 504 phantom at nominal thickness (left, a) and with ring (right, b). (c) Catphan spatial resolution module (CTP528). The line pair objects are oriented in a circular fashion. (d) MTF bead with an indication of the finite bead diameter. (e) Catphan low contrast resolution module (CTP515). The low contrast objects are oriented in a circular fashion. The 1.0% low contrast object ROI is shown on the right and the background ROI is shown on the left. (f) Catphan uniformity module (CTP486-2). ROIs were generated at the center and each of the four cardinal directions to evaluate uniformity. (g) Catphan sensitometry module (CTP404). Each ROI was generated in the center of the insert with an 8 mm diameter. The insert materials are listed adjacent to the insert.
FIG. 2.
FIG. 2.
Process of generating the MTF curve from the MTF bead intensity profile.
FIG. 3.
FIG. 3.
Wellhofer Scanditronix phantom used for dosimetric measurements. (Top left) Nominal phantom setup. (Top right) Example CBCT scan with nominal phantom setup and superimposed measurement locations on the surface and interior of the phantom. (Bottom left) Setup with additional phantom thickness. (Bottom right) Example CBCT scan with additional phantom thickness.
FIG. 4.
FIG. 4.
MTF data for nominal phantom thickness scans. (Left) MTF curve for the clinical head protocols for GE LightSpeed 16 slice and Varian OBI. The Elekta XVI HN S20 scan did not yield sufficient visualization of the MTF bead. Data points represent qualitative data, with the smallest visible line pair object given a MTF value of 10%, and the error bars representing half the increment of the line pair phantom. (Right) MTF curve for the clinical pelvis protocols for all three imaging systems.
FIG. 5.
FIG. 5.
CNR data for each imaging system at nominal Catphan phantom thickness (20.5 cm) and additional phantom thickness (30.5 cm). Error bars represent one standard deviation.
FIG. 6.
FIG. 6.
(Left) Uniformity index for each system, including results for nominal Catphan phantom thickness (20.5 cm) and results with additional phantom thickness (30.5 cm total thickness). The error bars represent the standard deviation. (Right) Horizontal intensity profiles through the uniformity module (CTP486-2) of the Catphan phantom. The OBI CBCT system is susceptible to ring artifacts in both geometries, while the XVI system exhibits cupping artifact in the nominal scan.
FIG. 7.
FIG. 7.
HU sensitivity data for each system with nominal phantom thickness: CT-to-ED curves have been constructed for each scan protocol. (Left) Varian OBI system. (Middle) Elekta XVI system. (Right) GE Lightspeed scanner.
FIG. 8.
FIG. 8.
HU sensitivity for each imaging system and scan protocol with varying phantom thickness. (Left) Varian OBI system. (Middle) Elekta XVI system. (Right) GE Lightspeed 16 slice scanner. Error bars represent one standard deviation.
FIG. 9.
FIG. 9.
Comparison of half trajectory scans at nominal thickness and with ring to full trajectory scans with ring for OBI Head protocol (left) and OBI Spotlight Protocol (right). Error bars represent one average standard deviation.
FIG. 10.
FIG. 10.
Calibration curves for each CBCT system.
See this image and copyright information in PMC

References

    1. Jaffray D. A. and Siewerdsen J., “Cone-beam computed tomography with a flat-panel imager: Initial performance characterization,” Med. Phys. 27, 1311–1323 (2000).10.1118/1.599009 - DOI - PubMed
    1. Zhong R., Wang J., Jiang X., He Y., Zhang H., Chen N., Bai S., and Xu F., “Hypofraction radiotherapy of liver tumor using cone beam computed tomography guidance combined with active breath control by long breath-holding,” Radiot. Oncol. 104, 379–385 (2012).10.1016/j.radonc.2011.11.007 - DOI - PubMed
    1. Nakagawa K., Yamashita H., Shiraishi K., Igaki H., Terahara A., Nakamura N., Ohtomo K., Saegusa S., Shiraki T., and Oritate T., “Verification of in-treatment tumor position using kilovoltage cone-beam computed tomography: A preliminary study,” Int. J. Radiat. Oncol., Biol., Phys. 69, 970–973 (2007).10.1016/j.ijrobp.2007.08.026 - DOI - PubMed
    1. Smitsmans M. H., De Bois J., Sonke J., Betgen A., Zijp L. J., Jaffray D. A., Lebesque J. V., and van Herk M., “Automatic prostate localization on cone-beam CT scans for high precision image-guided radiotherapy,” Int. J. Radiat. Oncol., Biol., Phys. 63, 975–984 (2005).10.1016/j.ijrobp.2005.07.973 - DOI - PubMed
    1. Purdie T. G., Moseley D. J., Bissonnette J., Sharpe M. B., Franks K., Bezjak A., and Jaffray D. A., “Respiration correlated cone-beam computed tomography and 4DCT for evaluating target motion in stereotactic lung radiation therapy,” Acta Oncol. 45, 915–922 (2006).10.1080/02841860600907345 - DOI - PubMed

Publication types