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Updated: Sep 20, 2025
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
Localization accuracy of 6-second CBCT for lung IGRT with various breathing patterns
Jihye Koo1, Gage Redler1, Vladimir Semenenko1
1Department of Radiation Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, USA.
Purpose:
The 6-second cone beam computed tomography (CBCT) acquisition of the Ethos HyperSight (Varian Medical Systems, Inc. Palo Alto, CA, USA) on-board imaging system offers benefits, but could be too fast to accurately capture an average target position in a free-breathing lung cancer patient. This study aimed to ascertain whether a 6-second acquisition is appropriate for regularly breathing patients with varying respiration periods. Additionally, breathing patterns that could lead to clinically impactful inaccuracies for image-guided radiation therapy (IGRT) shifts were investigated.
Methods:
Nine regular (sinusoidal) breathing patterns with different respiration rates (8-20 breaths-per-minute) and amplitudes, along with five irregular breathing patterns including a gasp/cough scenario, were tested using a respiratory motion phantom with a 3 cm diameter spherical target. Once the phantom was aligned using the external chassis to remove any default shifts, the 6-second CBCTs with Acuros reconstruction were acquired. Rigid registrations were performed using the 4DCT simulation average/untagged reconstructed image as reference to align to target (simulating clinical lung IGRT setup). Sixty-second CBCTs were also tested to verify the average offsets with conventional practice. The IGRT shifts were compared to 5 mm, a PTV margin typically used for lung tumors.
Results:
Minimal (<1.0 mm) shifts were observed for all regular breathing patterns with both 6-second and 60-second CBCT acquisitions. For moderately irregular breathing patterns and the gasp/cough scenario, all shifts were less than 5 mm. Shifts larger than 5 mm were observed in highly irregular breathing patterns, with both 6-second (14%) and 60-second (24%) CBCT acquisitions. Statistical tests showed no significant differences (p > 0.05) between the sizes of shifts made with the two CBCT durations.
Conclusion:
The 6-second CBCT can effectively and reliably localize a mobile target for regular and moderately-irregular breathers. Cautions should be used for highly irregular breathers, regardless of the duration of CBCT acquisition.
