Comparative study of respiratory motion correction techniques in cone-beam computed tomography

Background and purpose: To validate the clinical usefulness of motion-compensated (MC) cone-beam (CB) computed tomography (CT) for image-guided radiotherapy (IGRT) in comparison to four-dimensional (4D) CBCT and three-dimensional (3D) CBCT.

Material and methods: Forty-eight stereotactic body radiation therapy (SBRT) patients were selected. Each patient had 5-12 long CB acquisitions (4 min) and 1-7 short CB acquisitions (1 min), with a total of 349 and 150 acquisitions, respectively. 3D, 4D and MC CBCT images of every acquisition were reconstructed. Image quality, tumor positioning accuracy and tumor motion amplitude were quantified.

Results: The mean image quality of long short acquisitions, measured using the correlation ratio with the planning CT, was 74%/70%, 67%/47% and 79%/74% for 3D, 4D and MC CBCT, respectively; both 4D and MC CBCT were corrected for respiratory motion artifacts but 4D CBCTs suffered from streak artifacts. Tumor positioning with MC CBCT was significantly closer to 4D CBCT than 3D CBCT (p<0.0001). Detailed patient analysis showed that motion correction was not required for tumors with less than 1cm motion amplitude.

Conclusions: 4D and MC CBCT both allow accurate tumor position analysis under respiratory motion but 4D CBCT requires longer acquisition time than MC CBCT for adequate image quality. MC CBCT can therefore advantageously replace 4D CBCT in clinical protocols for patients with large motion to improve image quality and reduce acquisition time.