Low-dose megavoltage cone-beam CT imaging using thick, segmented scintillators.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Guidance

Background:

• Megavoltage, cone-beam computed tomography (MV CBCT) is crucial for soft-tissue visualization in image-guided radiotherapy.
• Conventional active matrix flat-panel imagers (AMFPIs) in electronic portal imaging devices (EPIDs) have low X-ray detection efficiency, requiring high radiation doses.
• Improving detective quantum efficiency (DQE) is key to achieving low-dose, high-quality imaging.

Purpose of the Study:

• To evaluate prototype AMFPIs with segmented crystalline scintillators for low-dose MV CBCT soft-tissue visualization.
• To assess the feasibility of using improved EPID technology for practical clinical applications.

Main Methods:

• Two prototype AMFPIs with segmented CsI:Tl and Bi(4)Ge(3)O(12) (BGO) crystalline scintillators (∼11 mm thick) were developed and tested.
• Bench-top CBCT system with a 6 MV photon beam was used for tomographic scans (180 projections, 360°).
• Image quality was assessed using spatial resolution and contrast-detail phantoms at low doses (∼4 cGy).

Main Results:

• Prototype AMFPIs demonstrated significantly improved DQE compared to conventional MV AMFPIs.
• Low contrast visualization was achieved, clearly delineating objects with a ∼2.76% electron density difference.
• Reconstructed images were obtained at a dose comparable to single portal images from conventional systems.

Conclusions:

• Segmented crystalline scintillators in AMFPIs offer a promising solution for low-dose, high-quality soft-tissue visualization in MV CBCT.
• These advancements pave the way for enhanced image-guided radiotherapy with reduced patient dose.
• Further evaluation is warranted to fully integrate this technology into clinical practice.