Preliminary study of a metal/a-Se-based portal detector

Area of Science:

• Medical Physics
• Radiological Imaging
• Materials Science

Background:

• Megavoltage portal imaging is crucial for radiotherapy verification.
• Existing portal imaging technologies have limitations in image quality and dose efficiency.
• Amorphous selenium (a-Se) offers potential for direct conversion X-ray detection.

Purpose of the Study:

• To investigate the feasibility of metal/amorphous selenium detectors for megavoltage portal imaging.
• To evaluate the sensitivity, dynamic range, and image quality of these detectors.
• To compare their performance against existing portal imaging systems.

Main Methods:

• Fabrication of metal/a-Se detectors with varying a-Se and metal plate thicknesses.
• Charging detectors via corona methods and digitizing images with a noncontact electrostatic probe.
• Assessing detector response to dose, electric field, and a-Se thickness; evaluating image quality using a contrast-detail phantom.

Main Results:

• A cubic relationship was observed between electrostatic voltage and radiation dose.
• Increased electric field enhanced sensitivity and dynamic range.
• Higher a-Se thickness increased sensitivity but reduced dynamic range; metal plate type had minimal impact.
• Image quality improved with increasing dose due to reduced quantum noise.

Conclusions:

• Metal/a-Se detectors are feasible for megavoltage portal imaging.
• Detector performance is influenced by electric field and a-Se thickness.
• These detectors offer superior contrast-detail imaging compared to some commercial systems at higher doses.