Comparative study of a low-Z cone-beam computed tomography system

Area of Science:

• Medical Imaging
• Radiological Physics
• Cone-Beam Computed Tomography

Background:

• Standard megavoltage (MV) imaging systems have limitations in contrast and radiation dose for diagnostic tasks.
• Kilovoltage (kV) imaging offers better contrast but is often unsuitable for volumetric imaging in radiation therapy settings.

Purpose of the Study:

• To evaluate an experimental low-atomic-number (Z) insert for a megavoltage cone-beam computed tomography (CBCT) system.
• To compare the imaging performance of the experimental system against standard MV and kV imaging modalities.

Main Methods:

• Acquisition of computed tomography images using a modified Elekta Precise linac with a low-Z insert.
• Production of low-energy photons via a medium-Z electron window and a low-Z carbon electron absorber.
• Utilized a detector sensitive to diagnostic x-ray energies for image acquisition.

Main Results:

• The low-Z imaging system demonstrated a contrast improvement of at least one order of magnitude over a standard 6 MV system.
• Achieved kilovoltage imaging contrast-to-noise ratio (0.15 cGy) at 11 cGy with the experimental system versus 244 cGy for the standard 6 MV system.
• Qualitative assessment showed kilovoltage-like images suitable for patient positioning acquired at 1-8 cGy with the low-Z system.

Conclusions:

• The experimental low-Z CBCT system offers superior contrast performance compared to standard MV systems.
• The system has the potential to provide diagnostic-quality images at significantly reduced radiation doses for applications like patient positioning.