Implementation and experimental evaluation of Mega-voltage fan-beam CT using a linear accelerator.

Area of Science:

• Medical Physics
• Radiological Imaging
• Radiation Therapy Physics

Background:

• Mega-voltage fan-beam Computed Tomography (MV-FBCT) offers potential for precise relative electron density (RED) and proton stopping power ratio (SPR) determination.
• However, MV-FBCT is not yet widely implemented in clinical practice.

Purpose of the Study:

• To demonstrate the feasibility of implementing MV-FBCT using a medical linear accelerator (LINAC) with a 2.5 MV imaging beam.
• To evaluate the accuracy of RED estimation using MV-FBCT compared to conventional CT.

Main Methods:

• Utilized multileaf collimators (MLCs) to collimate a 2.5 MV MV beam into a 1 cm fan-beam.
• Acquired projection data within one gantry rotation, applying in-house artifact correction algorithms.
• Established Hounsfield Unit (HU) to RED calibration curves using a CIRS phantom with tissue-mimicking inserts, comparing results with kilovoltage CT (TP-CT).

Main Results:

• In-house algorithms effectively reduced artifacts like ring and cupping.
• MV-FBCT demonstrated superior prediction accuracy for HU-RED calibration curves (R² > 0.9994) compared to TP-CT (R² < 0.9990).
• MV-FBCT accurately measured CT numbers for blood-iodine inserts, unlike TP-CT, and dose reduction to 30 MU did not impact accuracy.

Conclusions:

• Successfully demonstrated the feasibility of MV-FBCT using a LINAC, EPID, and MLCs.
• MV-FBCT shows significant potential for more accurate RED estimation in radiological imaging and radiation therapy planning.