4-Dimensional Cone Beam Computed Tomography-Measured Target Motion Underrepresents Actual Motion

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Oncology Imaging

Background:

• Four-dimensional cone beam computed tomography (4DCBCT) is crucial for accurate patient setup and tumor motion verification in lung stereotactic ablative body radiation therapy.
• Real-time motion quantification is essential for improving treatment accuracy and patient outcomes.

Purpose of the Study:

• To quantify the real-time motion represented in 4DCBCT scans.
• To evaluate the influence of different reconstruction algorithms and respiratory signals on motion quantification.

Main Methods:

• Eight lung cancer patients underwent 4DCBCT reconstruction using either the Feldkamp-Davis-Kress (FDK) algorithm or prior image constrained compressed sensing (PICCS).
• Real-time tumor motion was tracked using implanted electromagnetic Calypso beacons or an external respiratory signal (bellows belt).
• 4DCBCT-derived motion was compared against real-time beacon trajectories.

Main Results:

• 4DCBCT significantly underrepresented actual tumor motion in all directions (left-right, superior-inferior, anterior-posterior).
• Average underrepresentation ranged from 1.7 mm (LR) to 4.2 mm (SI).
• No statistically significant differences were observed between reconstruction algorithms or respiratory signal types in representing motion.

Conclusions:

• 4DCBCT consistently underestimates real-time lung tumor motion.
• The choice of reconstruction algorithm or respiratory signal does not affect the accuracy of motion range representation in 4DCBCT.