Interfractional Liver Positional Motion Under Exhaled Breath Holding Based on Cone Beam Computed Tomography

Area of Science:

• Radiation Oncology
• Medical Imaging
• Respiratory Motion Management

Background:

• Liver stereotactic body radiotherapy (SBRT) requires precise targeting.
• Respiratory motion significantly impacts liver tumor targeting accuracy.
• Exhaled breath holding (BH) is a technique to minimize respiratory motion during liver SBRT.

Purpose of the Study:

• To quantify interfractional liver positional motion during SBRT using exhaled BH.
• To assess the reliability of kilovoltage cone-beam computed tomography (kV-CBCT) for motion assessment in liver SBRT.
• To provide data for optimizing treatment margins and online correction strategies.

Main Methods:

• Collected 528 pre-treatment kV-CBCT images from 132 patients undergoing liver SBRT with exhaled BH.
• Utilized the Abches system for respiratory monitoring and planning CT acquisition under BH.
• Performed 3-DOF soft-tissue registration on kV-CBCT images after 6-DOF bone registration to determine liver motion in LR, AP, and CC directions.

Main Results:

• Mean interfractional liver positional motion was 0.7±1.0 mm (LR), 1.0±1.5 mm (AP), and 2.8±3.1 mm (CC).
• Systematic/random motions were 0.9/1.2 mm (LR), 1.4/1.8 mm (AP), and 2.9/3.9 mm (CC).
• Over 86% of interfractional motions were within 5 mm across all directions.

Conclusions:

• Exhaled BH effectively minimizes interfractional liver motion in SBRT.
• kV-CBCT is a valuable tool for monitoring liver position during SBRT with BH.
• Online correction guided by CBCT is recommended to address residual interfractional liver position errors.