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

• Published in: International journal of radiation oncology, biology, physics Vol. 73; no. 3; pp. 919 - 926
• Main Authors: Biederer, Juergen, Dinkel, Julien, Remmert, Gregor, Jetter, Siri, Nill, Simeon, Moser, Torsten, Bendl, Rolf, Thierfelder, Carsten, Fabel, Michael, Oelfke, Uwe, Bock, Michael, Plathow, Christian, Bolte, Hendrik, Welzel, Thomas, Hoffmann, Beata, Hartmann, Günter, Schlegel, Wolfgang, Debus, Jürgen, Heller, Martin, Kauczor, Hans-Ulrich
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2009
• Subjects: Animals; CHEST; Computed tomography; COMPUTERIZED TOMOGRAPHY; Cone beam CT; Cone-Beam Computed Tomography - methods; Dynamic MRI; Equipment Design; Hematology, Oncology and Palliative Medicine; LINEAR ACCELERATORS; Lung - diagnostic imaging; Lung - pathology; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - pathology; Lung nodules; LUNGS; Magnetic Resonance Imaging - methods; Movement; Multiple Pulmonary Nodules - diagnostic imaging; Multiple Pulmonary Nodules - pathology; NEOPLASMS; NMR IMAGING; Observer Variation; Particle Accelerators; PHANTOMS; Phantoms, Imaging; Radiology; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Reproducibility of Results; Respiration; Respiratory gating; SPATIAL RESOLUTION; Swine; Tomography, Spiral Computed - methods; Respiratory gating; Computed tomography; Dynamic MRI; Cone beam CT; Lung nodules
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2008.09.014

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). 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 × 1.2 mm, pitch 0.1, slice/increment 24×10 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 × 2.7 × 4.0 mm, temporal resolution 1.4 s) and linac-integrated 4D-CBCT (720 projections, 3-min rotation, temporal resolution ∼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. 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). 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.