【免费】论文研究-4D计算机断层扫描（4DCT）和4D锥形束计算机断层扫描（4DCBCT）的精度比较资源-CSDN文库

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International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 2017, 6, 323-335

http://www.scirp.org/journal/ijmpcero

ISSN Online: 2168-5444

ISSN Print: 2168-5436

DOI: 10.4236/ijmpcero.2017.63029

August 30, 2017

Accuracy Comparison of 4D Computed

Tomography (4DCT) and 4D Cone Beam

Computed Tomography (4DCBCT)

Tzu-Cheng Lee

, Stephen R. Bowen

2,3

, Sara St. James

, George A. Sandison

2,3

Paul E. Kinahan

1,2,3*

, Matthew J. Nyflot

2,3*

Department of Bioengineering, University of Washington, Seattle, WA, USA

Department of Radiation Oncology, University of Washington, Seattle, WA, USA

Department of Radiology, University of Washington, Seattle, WA, USA

Abstract

The ability of respiratory-correlated fan beam CT (4DCT) and respirat

ry-

correlated cone beam CT (4DCBCT) to accurately estimate tumor volume

is critical to accurate dosimetry and treatment verification for lung stereota

tic body radiation therapy (SBRT) and other motion-

managed therapies.

However, it is known that 4DCT and 4DCBCT differ in aspects of image a

quisition and reconstruction that may lead to discrepancies

between the two

modalities. To evaluate quantitative differences between 4DCT and 4DCBCT

imaging under respiratory motion, we performed a phantom study in the

ground truth setting. A programmable respiratory motion phantom was used

to simulate the 1D S-I position of a known-

size lesion. Ten sinusoidal and

twenty patient-specific breathing waveforms were applied to drive lesion m

tion during the 4DCT and 4DCBCT acquisitions. The difference in lesion v

lume acquired between the two imaging modalities was as h

igh as 34.4% and

18.4% for sinusoidal and patient-

specific breathing motions, respectively.

When compared to the true volume, 4DCT measurement often underest

mated the lesion size whereas 4DCBCT overestimated the lesion volume in

most of the cases. 4DCBCT

gave more accurate recovery of the volume than

4DCT for most settings tested in this study. These findings may be helpful for

improving the definition of internal target and planning target volume ma

gins, and extracting quantitative information from on-board treatment verif

cation imaging.

Keywords

4DCT, 4DCBCT, Verification Imaging, Respiratory Motion Phantom

How to cite this paper:

Lee, T.-C., Bowen,

.R., St. James, S., Sandison, G.

A., Kinahan,

.E. and Nyflot, M.J. (2017) Accuracy Com-

parison of 4D Computed Tomography

(4DCT) and 4D Cone Beam Computed

Tomography (4DCBCT)

International

Journal of

Medical Physics

Clinical

Engineering and Radiation Oncology

323

-335.

https://doi.org/10.4236/ijmpcero.2017.63029

Received:

July 25, 2017

Accepted:

August 27, 2017

Published:

August 30, 2017

7 by authors and

Scientific

Research Publishing Inc.

This work is licensed under the Creative

Commons Attribution International

License (CC BY

4.0).

http://creativecommons.org/licenses/by/4.0/

Open Access

T.-C. Lee et al.

324

1. Introduction

Accurate computed tomography (CT) studies under the presence of respiratory

motion are necessary for treatment planning, treatment verification, and adap-

tive radiotherapy in many cancers, most commonly for cancers of the lung, liver,

and abdomen [1] [2] [3] [4] [5]. 4DCT imaging may be used for respiratory mo-

tion assessment and creating an external beam radiation treatment plan for a

free-breathing patient [6] [7]. Radiotherapy image-guided verification is com-

monly performed by comparing lesion position and motion estimated in the

treatment room with cone beam CT (CBCT), CT on rails, megavoltage CT

(MVCT) or other methods to the primary planning CT study acquired at the

time of treatment simulation. Beyond the critical role of verification imaging in

patient setup, changes in CT volumes have been used as indications for adaptive

re-planning and modeled to extract radiobiological parameters [8] [9].

It is known that respiratory motion leads to significant imaging artifacts

which may lead to incorrect treatment planning volumes, lesion localization, or

inference of change in tumor volume over time. Respiratory-correlated com-

puted tomography (4DCT) using external respiratory surrogates was first pro-

posed as solution for this problem [10] [11] [12] [13] and has rapidly become a

standard of care for radiotherapy simulation in the presence of respiratory mo-

tion [14] [15]. In the intervening years, cone beam computed tomography

(CBCT) technology has proliferated on linear accelerators to provide image

guidance for radiotherapy verification, and recently, respiratory-correlated cone

beam CT (4DCBCT) has become clinically available [16] [17] [18]. Sonke

et al.

investigated 4DCBCT versus 3DCBCT and fluoroscopy and found motion arti-

facts in 4D dataset were substantially reduced compared to a 3D scan [17].

Sweeney

et al.

investigated inter-observer variability of target localization for

4DCBCT and 3DCBCT imaging with patient data and found significantly re-

duced variability with 4DCBCT [19]. Lee

et al.

and Iramina

et al.

further ex-

amined the impact of scanning parameters and motion sorting methods related

to the accuracy of 4DCBCT images [20] [21].

However, clinical investigation of comparisons of 4DCBCT and 4DCT imag-

ing for tumor motion assessment has indicated significant differences in some

patients [22]. 4DCT and 4DCBCT imaging differs in numerous aspects in terms

of image acquisition, hardware geometry, and binning techniques [23] [24].

These differences include smaller x-ray beam volumetric coverage in CT versus

much larger coverage in CBCT for a single rotation, scan time on the order of

seconds in 4DCT versus minutes in 4DCBCT, arc detector versus flat panel de-

tector geometry employed with different anti-scatter setups, and external surro-

gates in 4DCT versus internal tracking in 4DCBCT of respiratory motion. To

date, investigations of accuracy of respiratory-correlated fan beam versus cone

beam CT imaging in the presence of respiratory motion in the ground truth set-

ting have been limited. Researchers have compared 3DCBCT image to the 4DCT

maximum intensity projection (MIP) reconstructed image of anthropomorphic

respiratory phantoms and found contradictory results [25] [26]. Nevertheless,

T.-C. Lee et al.

325

the relative accuracy of 4DCBCT and 4DCT in the ground truth setting is un-

known.

We had shown the uptake accuracy in 4D phased-match CT attenuation cor-

rected 4DPET could be significantly compromised due to patient’s irregular

breathing pattern and the nature of acquisition time difference between two

modalities [27]. In this work, we will focus on the impact of respiratory motion

on CT acquisition by comparing the accuracy of 4DCT and 4DCBCT in the

ground truth setting with an anthropomorphic respiratory phantom. These re-

sults may be informative for treatment planning, treatment verification, longitu-

dinal response assessment, and adaptive radiotherapy for thoracic and abdomin-

al cancers.

2. Methods

2.1. Anthropomorphic Phantom

The Quasar programmable respiratory motion phantom (Modus Medical De-

vices Inc., ON, Canada) was used for this study. A custom insert was designed,

consisting of a water-filled 24 mm outer-diameter sphere simulating a lung le-

sion, surrounded by polystyrene pellets comparable to the density of lung. The

Quasar phantom has a mount for an infrared marker which moves at a 1:1 ratio

to the phantom insert. The motion of the infrared marker was captured with an

RPM camera (RPM, Varian Medical Systems, Palo Alto, CA). An image of the

phantom is shown in

Figure 1. The motion of the Quasar phantom is one di-

mensional (superior-inferior) and can be programmed using sinusoidal breath-

ing traces or representative patient traces distributed with the phantom.

2.2. Phantom Motion

To evaluate the fidelity of the 4DCT and 4DCBCT studies, the water sphere was

driven by 10 sinusoidal respiratory waveforms (period 3, 4, 5, 6, 7 seconds, 15

and 30 mm amplitude) and 20 patient-derived respiratory waveforms provided

by the Quasar software (10 patient waveforms with period 4.2 ± 0.7 - 6.6 ± 1.6

seconds, nominal 15 and 30 mm peak-to-peak amplitude, mean 9.9 ± 1.2 - 19.8

± 2.3 mm amplitude). It should be noted that the patient-specific respiratory

Figure 1. On left, programmable respiratory phantom with custom anthropomorphic in-

sert. The mount for the infrared marker cubic is indicated with a red arrow. On right,

representative CT slice of phantom geometry.

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