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. 2009 Jun 17;10(3):37-48.
doi: 10.1120/jacmp.v10i3.3023.

Image quality & dosimetric property of an investigational imaging beam line MV-CBCT

Chris Beltran  1 , Renin Lukose  1 , Bijumon Gangadharan  2 , Ali Bani-Hashemi  2 , Bruce A Faddegon  3
Affiliations

Image quality & dosimetric property of an investigational imaging beam line MV-CBCT

Chris Beltran et al. J Appl Clin Med Phys. .

Abstract

To measure and compare the contrast to noise ratio (CNR) as a function of dose for the CBCTs produced by the mega-voltage (MV) imaging beam line (IBL) and the treatment beam line (TBL), and to compare the dose to target and various critical structures of pediatric patients for the IBL CBCT versus standard TBL orthogonal port films. Two Siemens Oncor linear accelerators were modified at our institution such that the MV-CBCT would operate under an investigational IBL rather than the standard 6MV TBL. Prior to the modification, several CBCTs of an electron density phantom were acquired with the TBL at various dose values. After the modification, another set of CBCTs of the electron density phantom were acquired for various doses using the IBL. The Contrast to Noise Ratio (CNR) for each tissue equivalent insert was calculated. In addition, a dosimetric study of pediatric patients was conducted comparing the 1 cGy IBL CBCT and conventional TBL orthogonal pair port films. The CNR for eight tissue equivalent inserts at five different dose settings for each type of CBCT was measured. The CNR of the muscle insert was 0.8 for a 5 cGy TBL CBCT, 1.1 for a 1.5 cGy IBL CBCT and 2.8 for a conventional CT. The CNR of the trabecular bone insert was 2.9 for a 5 cGy TBL CBCT, 5.5 for a 1.5 cGy IBL CBCT and 14.8 for a conventional CT. The IBL CBCT delivered approximately one-fourth the dose to the target and critical structures of the patients as compared to the TBL orthogonal pair port films. The IBL CBCT improves image quality while simultaneously reducing the dose to the patient as compared to the TBL CBCT. A 1 cGy IBL CBCT, which is used for boney anatomy localization, delivers one-fourth the dose as compared to conventional ortho-pair films.

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Figures

Figure 1
Figure 1
Image (left) and CT (right) of the heterogeneity phantom. The regions of interests shown on the CT are the same that are used for the various CBCTs.
Figure 2
Figure 2
The center slice of the heterogeneity phantom with corresponding regions of interests for a 2 cGy IBL CBCT (left) and a 5 cGy TBL CBCT (right).
Figure 3
Figure 3
The relative dose distribution for the TBL (left) and IBL (right) CBCT. The 100% line intersects the isocenter.
Figure 4
Figure 4
Graph of the CNR for the low‐contrast medium in the phantom for the Imaging Beam Line (solid) and Treatment Beam Line (dashed) CBCTs.
Figure 5
Figure 5
Graph of the CNR for the high‐contrast medium in the phantom for the Imaging Beam Line (solid) and Treatment Beam Line (dashed) CBCTs.
Figure 6
Figure 6
The dose distributions, normalized to isocenter, on transverse, coronal and sagittal planes along the isocenter of a cranial and a body patient for an IBL CBCT and ortho‐pair plan.
Figure 7
Figure 7
The CBCT (solid) and ortho‐pair (dashed) Dose Volume Histograms (DVH) for the clinical target volume (CTV) of the 23 cranial patients.
Figure 8
Figure 8
The CBCT (solid) and ortho‐pair (dashed) Dose Volume Histograms (DVH) for the optic chiasm of the 23 cranial patients.
Figure 9
Figure 9
The CBCT (solid) and ortho‐pair (dashed) Dose Volume Histograms (DVH) for the left kidney of the 10 body patients.
Figure 10
Figure 10
An image of a 1 cGy IBL CBCT for a 4‐year‐old female patient.
See this image and copyright information in PMC

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