Accuracy Comparison of 4D Computed Tomography (4DCT) and 4D Cone Beam Computed Tomography (4DCBCT)

Abstract

The ability of respiratory-correlated fan beam CT (4DCT) and respiratory-correlated cone beam CT (4DCBCT) to accurately estimate tumor volume is critical to accurate dosimetry and treatment verification for lung stereotactic body radiation therapy (SBRT) and other motion-managed therapies. However, it is known that 4DCT and 4DCBCT differ in aspects of image acquisition 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 motion during the 4DCT and 4DCBCT acquisitions. The difference in lesion volume acquired between the two imaging modalities was as high as 34.4% and 18.4% for sinusoidal and patient-specific breathing motions, respectively. When compared to the true volume, 4DCT measurement often underestimated 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 margins, and extracting quantitative information from on-board treatment verification imaging.

On the evaluation of mobile target trajectory between four‐dimensional computer tomography and four‐dimensional cone‐beam computer tomography

“…Previous studies have also demonstrated that 4D CBCT accurately assesses target volume. 21 It may also be useful to include 4D CBCT imaging in the treatment planning process for conventional fractionation to more accurately determine ITV, where clinics lack 4D CT capabilities but have 4D CBCT.…”

“…Additionally, 4D CT has been shown to suffer from motion artifacts leading to 4D CBCT better evaluating target volumes when using a motion phantom with a few different sinusoidal and patient specific motion parameters. 21 Lastly, phantom target motion between the two imaging modalities has been shown to be comparable but with very few different motion parameters explored. 22 These studies, however, have not explored how a wide variety of combinations of amplitude and cycle time for the target motion affect the agreement between 4D CT and 4D CBCT evaluation of target trajectories and where evaluation is hindered due to artifacts.…”

“…It is challenging though to determine if these discrepancies are due to patient‐related factors or inherent differences in the imaging modalities. Additionally, 4D CT has been shown to suffer from motion artifacts leading to 4D CBCT better evaluating target volumes when using a motion phantom with a few different sinusoidal and patient specific motion parameters 21 . Lastly, phantom target motion between the two imaging modalities has been shown to be comparable but with very few different motion parameters explored 22 .…”

Image-guided radiotherapy using 4D cone-beam computed tomography

“…For treatment planning, treatment verification, and adaptive radiation in many malignancies, accurate Computed Tomography (CT) studies in the presence of respiratory motion are required [1]. The use of radiotherapy for lung cancer is growing, with Stereotactic Ablative Radiotherapy (SABR) currently being recommended as the first-line therapy for patients with Stage I NSCLC who are medically inoperable and require non-invasive treatment options [2].…”

“…ITV is calculated through examination of the Four-Dimensional Computed Tomography (4DCT) images in the case of tumors moving with respiration, such as lung cancer [8]. The radiotherapy plans are typically created using ITV along with setup margins [1,5,8,9]. Comparing the Cone Beam CT (CBCT) acquired prior to treatment with estimated target position and motion to the primary planning CT scan acquired during the simulation is a standard method for doing radiotherapy image-guided verification [10].…”