TITLE:
Effects of Irregular Respiratory Motion on the Positioning Accuracy of Moving Target with Free Breathing Cone-Beam Computerized Tomography
AUTHORS:
Xiang Li, Tianfang Li, Ellen Yorke, Gig Mageras, Xiaoli Tang, Maria Chan, Weijun Xiong, Marsha Reyngold, Richard Gewanter, Abraham Wu, John Cuaron, Margie Hunt
KEYWORDS:
Cone Beam Computerized Tomography, Respiratory Motion Effect
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.2,
May
8,
2018
ABSTRACT: For positioning a moving target, a maximum intensity
projection (MIP) or average intensity projection (AIP) image derived from 4DCT
is often used as the reference image which is matched to free breathing
cone-beam CT (FBCBCT) before treatment. This method can be highly accurate if
the respiratory motion of the patient is stable. However, a patient’s breathing
pattern is often irregular. The purpose of this study is to investigate the
effects of irregular respiration on positioning accuracy for a moving target
aligned with FBCBCT. Nine patients’ respiratory motion curves were selected to
drive a Quasar motion phantom with one embedded cubic and two spherical
targets. A 4DCT of the phantom was acquired on a CT scanner (Philips Brilliance
16) equipped with a Varian RPM system. The phase binned 4DCT images and the
corresponding MIP and AIP images were transferred into Eclipse for analysis.
FBCBCTs of the phantom driven by the same respiratory curves were also acquired
on a Varian TrueBeam and fused such that both CBCT and MIP/AIP images share the
same target zero positions. The sphere and cube volumes and centroid
differences (alignment error) determined by MIP, AIP and FBCBCT images were
calculated, respectively. Compared to the volume determined by MIP, the volumes
of the cube, large sphere, and small sphere in AIP and FBCBCT images were
smaller. The alignment errors for the cube, large sphere and small sphere with
center to center matches between MIP and FBCBCT were 2.5 ± 1.8 mm, 2.4 ± 2.1 mm, and 3.8 ± 2.8 mm, and the alignment errors between AIP and FBCBCT
were 0.5 ± 1.1 mm, 0.3 ± 0.8 mm, and
1.8 ± 2.0 mm,
respectively. AIP images appear to be superior reference images to MIP images.
However, irregular respiratory pattern could compromise the positioning
accuracy, especially for smaller targets.