Localization accuracy of 6-second CBCT for lung IGRT with various breathing patterns

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• On-board imaging systems, such as the Ethos HyperSight, offer benefits for radiation therapy.
• Rapid imaging acquisitions, like 6-second cone beam computed tomography (CBCT), may pose challenges for accurately capturing target motion in free-breathing lung cancer patients.

Purpose of the Study:

• To evaluate the appropriateness of a 6-second CBCT acquisition for patients with regular and varying respiration periods.
• To investigate breathing patterns that could lead to clinically significant inaccuracies in image-guided radiation therapy (IGRT) shifts.

Main Methods:

• A respiratory motion phantom with a spherical target simulated regular and irregular breathing patterns.
• 6-second and 60-second CBCT acquisitions were performed using Acuros reconstruction.
• Rigid registrations compared IGRT shifts to a 5 mm planning target volume (PTV) margin.

Main Results:

• All regular breathing patterns showed minimal shifts (<1.0 mm) for both acquisition durations.
• Shifts remained under 5 mm for moderately irregular breathing and gasp/cough scenarios.
• Highly irregular breathing patterns resulted in shifts exceeding 5 mm in 14% of 6-second CBCTs and 24% of 60-second CBCTs, with no significant difference between durations.

Conclusions:

• The 6-second CBCT reliably localizes mobile targets in regular and moderately irregular breathers.
• Caution is advised for patients with highly irregular breathing patterns, irrespective of CBCT acquisition time.