Low-dose 2.5 MV cone-beam computed tomography with thick CsI flat-panel imager

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Diagnostic Imaging

Background:

• Megavoltage (MV) portal imagers are common in radiotherapy but limited for volumetric imaging due to poor quality with high-energy beams (>6MV).
• A prototype 2.5 MV imaging beam offers a potential solution for improved MV imaging.

Purpose of the Study:

• To evaluate the feasibility of low-dose megavoltage cone-beam imaging using a 2.5 MV beam and a high-efficiency cesium iodide detector.
• To assess the imaging properties, image quality, and dose efficiency of this prototype system.

Main Methods:

• Assessed basic imaging properties (spatial resolution, modulation transfer function) of the 2.5 MV prototype.
• Acquired megavoltage cone-beam scans of an anthropomorphic phantom (head, thorax, pelvis) and compared them to kilovoltage cone-beam (kV-CBCT) and 6 MV cone-beam (6X-CBCT) images.
• Scanned a phantom with metallic inserts, comparing image quality to CT and kV-CBCT.

Main Results:

• The 2.5 MV system generally yielded better image quality than the 6 MV system, with improved contrast-to-noise ratio for bone-to-tissue in phantom studies.
• Imaging dose for 2.5 MV cone-beam images was significantly lower (2.4-3.4 MU) compared to 6 MV cone-beam scans (26 MU) for comparable image quality sufficient for bony alignment.
• The 2.5 MV system did not produce high-Z image artifacts, unlike kV-CBCT, making it suitable for cases with high-Z prostheses.

Conclusions:

• The 2.5 MV prototype imaging system demonstrates feasibility for low-dose, high-quality megavoltage cone-beam imaging.
• This technology offers advantages over conventional 6 MV MV imaging and kV-CBCT, particularly in dose reduction and artifact avoidance.
• The system shows promise for enhancing radiotherapy treatment planning, especially in the presence of metallic implants.