Sci-Thurs PM: Delivery-10: Marker trajectory reconstruction using cone-beam CT projection images

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Guidance

Background:

• Image guidance and daily verification are crucial in modern radiotherapy, particularly for moving targets.
• Assessing target motion from integrated 3D cone-beam CT (CBCT) images is challenging.
• Fiducial markers in moving targets are identifiable in raw CBCT projection data.

Purpose of the Study:

• To develop and validate a method for extracting 4D trajectory information from discarded CBCT projection data.
• To accurately measure the motion of targets during radiotherapy using readily available imaging data.
• To improve the precision of image guidance for treating moving targets in radiotherapy.

Main Methods:

• Utilized raw projection images from CBCT scans of a moving phantom with a fiducial marker.
• Determined fiducial marker location in each projection image and assigned a 'breath phase'.
• Reconstructed 3D positions using pairs of orthogonal images at the same breath phase from different cycles to determine the 4D trajectory.

Main Results:

• The reconstructed average trajectory achieved an accuracy of less than 1mm compared to the true motion.
• Demonstrated accurate measurement of the 4D trajectory in an ideal case with identical motion cycles.
• Successfully extracted trajectory information from discarded CBCT projection data.

Conclusions:

• The developed method accurately measures 4D trajectories from CBCT projection data, offering potential for improved radiotherapy.
• This technique shows promise for enhancing image guidance and daily verification in treating moving targets.
• Future work will focus on applying this tool to more complex, non-identical patient motion patterns.