Four-dimensional cone beam CT with adaptive gantry rotation and adaptive data sampling

Area of Science:

• Medical Physics
• Radiological Imaging
• Radiation Oncology

Background:

• Image-guided radiation therapy (IGRT) systems require accurate patient positioning.
• Motion artifacts from patient respiration can degrade image quality in CT imaging.
• Four-dimensional CT (4D-CT) addresses respiratory motion by acquiring data throughout the breathing cycle.

Purpose of the Study:

• To develop and evaluate a novel four-dimensional cone beam CT (4D-CBCT) integrated into an IGRT system.
• To assess the feasibility of 4D-CBCT for maintaining image quality and radiation dose comparable to conventional CT.
• To demonstrate the clinical applicability of 4D-CBCT for patient treatment.

Main Methods:

• Adapted Varian CBCT system gantry rotation speed to patient's average breath cycle.
• Utilized real-time positioning and monitoring to record respiratory signals during CBCT acquisition.
• Employed full-fan bowtie filter, 200-degree gantry rotation, and half-scan cone beam reconstruction.

Main Results:

• Scan times ranged from 3.3 to 6.6 minutes for a 200-degree rotation.
• Radiation dose was approximately 1-2 times that of conventional 4D-CT.
• Phantom studies confirmed scanning, data processing, and image quality.
• Patient studies demonstrated clinical applicability, though 4D-CT had higher contrast-to-noise ratio (2.8-3.5x).

Conclusions:

• The developed 4D-CBCT system is clinically applicable for IGRT.
• The system effectively manages respiratory motion while maintaining acceptable image quality and radiation dose.
• Further optimization may be needed to match the contrast-to-noise ratio of conventional 4D-CT.