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

Colton Baley, Neil Kirby, Timothy Wagner, Nikos Papanikolaou, Pamela Myers, Karl Rasmussen, Sotirios Stathakis, Daniel Saenz

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Purpose: For mobile lung tumors, four-dimensional computer tomography (4D CT) is often used for simulation and treatment planning. Localization accuracy remains a challenge in lung stereotactic body radiation therapy (SBRT) treatments. An attractive image guidance method to increase localization accuracy is 4D cone-beam CT (CBCT) as it allows for visualization of tumor motion with reduced motion artifacts. However, acquisition and reconstruction of 4D CBCT differ from that of 4D CT. This study evaluates the discrepancies between the reconstructed motion of 4D CBCT and 4D CT imaging over a wide range of sine target motion parameters and patient waveforms. Methods: A thorax motion phantom was used to examine 24 sine motions with varying amplitudes and cycle times and seven patient waveforms. Each programmed motion was imaged using 4D CT and 4D CBCT. The images were processed to auto segment the target. For sine motion, the target centroid at each phase was fitted to a sinusoidal curve to evaluate equivalence in amplitude between the two imaging modalities. The patient waveform motion was evaluated based on the average 4D data sets. Results: The mean difference and root-mean-square-error between the two modalities for sine motion were −0.35 ± 0.22 and 0.60 mm, respectively, with 4D CBCT slightly overestimating amplitude compared with 4D CT. The two imaging methods were determined to be significantly equivalent within ±1 mm based on two one-sided t tests (p < 0.001). For patient-specific motion, the mean difference was 1.5 ± 2.1 (0.8 ± 0.6 without outlier), 0.4 ± 0.3, and 0.8 ± 0.6 mm for superior/inferior (SI), anterior/posterior (AP), and left/right (LR), respectively. Conclusion: In cases where 4D CT is used to image mobile tumors, 4D CBCT is an attractive localization method due to its assessment of motion with respect to 4D CT, particularly for lung SBRT treatments where accuracy is paramount.

Original languageEnglish (US)
Pages (from-to)198-207
Number of pages10
JournalJournal of Applied Clinical Medical Physics
Issue number7
StatePublished - Jul 2021


  • 4D CBCT
  • 4D CT
  • SBRT
  • lung cancer
  • motion management

ASJC Scopus subject areas

  • Instrumentation
  • Radiation
  • Radiology Nuclear Medicine and imaging


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