Geometrical differences in gross target volumes between 3DCT and 4DCT imaging in radiotherapy for non-small-cell lung cancer

Abstract

The aim of this study was to explore the characteristic of 3DCT scanning phases and estimate the comparative amount of respiration motion information included in 3DCT and 4DCT by comparing the volumetric and positional difference between the volumes from 3DCT and 4DCT for the radiotherapy of non-small-cell lung cancer (NSCLC). A total of 28 patients with NSCLC sequentially underwent 3DCT and 4DCT simulation scans of the thorax during free breathing. The 4DCT images with respiratory signal data were reconstructed and sorted into 10 phases throughout a respiratory cycle. GTV-3D from 3DCT, GTV-0%, GTV-20%, GTV-50% and GTV-70% from end-inspiration, mid-expiration, end-expiration and mid-inspiration of 4DCT, and the internal GTV (IGTV-10) from the fused phase of 4DCT were delineated based on the 50% phase image, respectively. The differences in the position, size, matching index (MI) and degree of inclusion (DI) for different volumes were evaluated. The variation in the centroid shifts of GTV-0% and GTV-3D, GTV-20% and GTV-3D, GTV-50% and GTV-3D, and GTV-90% and GTV-3D in the 3D direction was not significant (P = 0.990). The size ratios of GTV-0%, GTV-20%, GTV-50%, GTV-70% and IGTV-10 to GTV-3D were 0.94 ± 0.18, 0.95 ± 0.18, 0.98 ± 0.15, 1.00 ± 0.18 and 1.60 ± 0.55, respectively. DIs of GTV-3D in IGTV-10, and IGTV-10 in GTV-3D were 0.88 ± 0.14 and 0.59 ± 0.16 (P < 0.001). The 3DCT scanning phases are irregular. The CTV-to-ITV expansion should be isotropic when defining the ITV on the 3DCT. The internal GTV derived from 4DCT cannot completely include the GTV from 3DCT. An additional margin may be required when defining the ITV-based 4DCT.

A comparative study of target volumes based on ¹⁸F-FDG PET-CT and ten phases of 4DCT for primary thoracic squamous esophageal cancer

“…One approach to define tumor motion is to contour gross target volumes (GTVs) on ten phases of 4DCT and obtain internal gross target volume (IGTV) by combining them; theoretically, this would give information about the entire tumor motion 7,8…”

A comparison of dosimetric variance for external-beam partial breast irradiation using three-dimensional and four-dimensional computed tomography

“… 6 Temporal images acquired during conventional axial three-dimensional computed tomography (3DCT) may include limited respiratory motion details for determining the target margin, but it has been difficult to evaluate how much motion information the 3DCT provides. 7 In contrast, the four-dimensional computed tomography (4DCT) is a reliable and effective tool for assessing tumor motion. 8 4DCT enables the correlation of CT data acquisition with respiratory cycles, facilitating the acquisition of a series of 3DCT data sets over a patient’s breathing cycle to provide visualization of tumor motion on an individual patient basis.…”

Development of an Advanced Deformable Phantom to Analyze Dose Differences due to Respiratory Motion

“…Several studies showed that lower lobe tumor motions occurred mostly in the SI direction and had larger amplitude movement than upper lobe tumors. 18,19) In addition, large tumor motion may be more closely associated with the difference between the 3D and 4D dose calculations than small motion. Therefore, the phantom simulated a tumor located in the lower lobe.…”