4D-Imaging of the lung: reproducibility of lesion size and displacement on helical CT, MRI, and cone beam CT in a ventilated ex vivo system.
OBJECTIVE
Four-dimensional (4D) imaging is a key to motion-adapted radiotherapy of lung tumors. We evaluated in a ventilated ex vivo system how size and displacement of artificial pulmonary nodules are reproduced with helical 4D-CT, 4D-MRI, and linac-integrated cone beam CT (CBCT).


METHODS
Four porcine lungs with 18 agarose nodules (mean diameters 1.3-1.9 cm), were ventilated inside a chest phantom at 8/min and subject to 4D-CT (collimation 24 x 1.2 mm, pitch 0.1, slice/increment 24 x 10(2)/1.5/0.8 mm, pitch 0.1, temporal resolution 0.5 s), 4D-MRI (echo-shared dynamic three-dimensional-flash; repetition/echo time 2.13/0.72 ms, voxel size 2.7 x 2.7 x 4.0 mm, temporal resolution 1.4 s) and linac-integrated 4D-CBCT (720 projections, 3-min rotation, temporal resolution approximately 1 s). Static CT without respiration served as control. Three observers recorded lesion size (RECIST-diameters x/y/z) and axial displacement. Interobserver- and interphase-variation coefficients (IO/IP VC) of measurements indicated reproducibility.


RESULTS
Mean x/y/z lesion diameters in cm were equal on static and dynamic CT (1.88/1.87; 1.30/1.39; 1.71/1.73; p > 0.05), but appeared larger on MRI and CBCT (2.06/1.95 [p < 0.05 vs. CT]; 1.47/1.28 [MRI vs. CT/CBCT p < 0.05]; 1.86/1.83 [CT vs. CBCT p < 0.05]). Interobserver-VC for lesion sizes were 2.54-4.47% (CT), 2.29-4.48% (4D-CT); 5.44-6.22% (MRI) and 4.86-6.97% (CBCT). Interphase-VC for lesion sizes ranged from 2.28% (4D-CT) to 10.0% (CBCT). Mean displacement in cm decreased from static CT (1.65) to 4D-CT (1.40), CBCT (1.23) and MRI (1.16).


CONCLUSIONS
Lesion sizes are exactly reproduced with 4D-CT but overestimated on 4D-MRI and CBCT with a larger variability due to limited temporal and spatial resolution. All 4D-modalities underestimate lesion displacement.
Biederer
Juergen
J
Department of Diagnostic Radiology, University Hospital Schleswig-Holstein, Campus Kiel, Germany. juergen.biederer@rad.uni-kiel.de
Dinkel
Julien
J
Remmert
Gregor
G
Jetter
Siri
S
Nill
Simeon
S
Moser
Torsten
T
Bendl
Rolf
R
Thierfelder
Carsten
C
Fabel
Michael
M
Oelfke
Uwe
U
Bock
Michael
M
Plathow
Christian
C
Bolte
Hendrik
H
Welzel
Thomas
T
Hoffmann
Beata
B
Hartmann
Günter
G
Schlegel
Wolfgang
W
Debus
Jürgen
J
Heller
Martin
M
Kauczor
Hans-Ulrich
HU
D000818:Animals; D054893:Cone-Beam Computed Tomography / Q000379:methods; D004867:Equipment Design; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D009068:Movement; D055613:Multiple Pulmonary Nodules / Q000000981:diagnostic imaging / Q000473:pathology; D015588:Observer Variation; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012119:Respiration; D013552:Swine; D036542:Tomography, Spiral Computed / Q000379:methods