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.
Highlights
It is known that 4DCT and 4DCBCT differ in aspects of image acquisition and reconstruction that may lead to discrepancies between the two modalities
Accurate computed tomography (CT) studies under the presence of respiratory motion are necessary for treatment planning, treatment verification, and adaptive radiotherapy in many cancers, most commonly for cancers of the lung, liver, and abdomen [1] [2] [3] [4] [5]. 4DCT imaging may be used for respiratory motion assessment and creating an external beam radiation treatment plan for a free-breathing patient [6] [7]
When the amplitude was increased to 30 mm, the magnitude of underestimation was greater for 4DCT at 5.58 ± 1.36 mL, while average volumes measured by 4DCBCT were not greatly changed at 8.21 ± 0.23 mL
Summary
Accurate computed tomography (CT) studies under the presence of respiratory motion are necessary for treatment planning, treatment verification, and adaptive radiotherapy in many cancers, most commonly for cancers of the lung, liver, and abdomen [1] [2] [3] [4] [5]. 4DCT imaging may be used for respiratory motion assessment and creating an external beam radiation treatment plan for a free-breathing patient [6] [7]. Accurate computed tomography (CT) studies under the presence of respiratory motion are necessary for treatment planning, treatment verification, and adaptive radiotherapy in many cancers, most commonly for cancers of the lung, liver, and abdomen [1] [2] [3] [4] [5]. Radiotherapy image-guided verification is commonly performed by comparing lesion position and motion estimated in the treatment room with cone beam CT (CBCT), CT on rails, megavoltage CT (MVCT) or other methods to the primary planning CT study acquired at the time of treatment simulation. Lee et al and Iramina et al further examined the impact of scanning parameters and motion sorting methods related to the accuracy of 4DCBCT images [20] [21]
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