Technical Note: Volumetric computed tomography for radiotherapy simulation and treatment planning.

Purpose: For lung and liver tumors requiring radiotherapy, motion artifacts are common in 4D-CT images due to the small axial field-of-view (aFOV) of conventional CT scanners. This may negatively impact contouring and dose calculation accuracy and could lead to a geographic miss during treatment. Recent advancements in volumetric CT (vCT) enable an aFOV up to 160 mm in a single rotation, which may reduce motion artifacts. However, the impact of large aFOV on CT number required for dose calculation needs to be evaluated before clinical implementation. The objective of this study was to determine the utility of a 256-slice vCT scanner for 4D-CT simulation by evaluating image quality and generating relative electron density (RED) curves.

Methods: Images were acquired on a 256-slice GE Revolution CT scanner with 40 mm, 80 mm, 120 mm, 140 mm, and 160 mm aFOV. Image quality was assessed by evaluating CT number linearity, uniformity, noise, and low-contrast resolution. The relationship between each quality metric and aFOV was assessed.

Results: CT number linearity, uniformity, noise, and low-contrast resolution were within the expected range for each image set, except CT number in Teflon and Delrin, which were underestimated. Spearman correlation coefficient (ρ) showed that the CT number for Teflon (ρ = 1.0, p = 0.02), Delrin (ρ = 1.0, p = 0.02), and air (ρ = 1.0, p = 0.02) was significantly related to aFOV, while all other measurements were not. The measured deviations from expected values were not clinically significant.

Conclusion: These results suggest that vCT can be used for CT simulation for radiation treatment planning.