High-DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: performance evaluation at extremely low dose

Area of Science:

• Medical Physics
• Radiotherapy Imaging
• Detector Technology

Background:

• Active matrix, flat-panel imagers (AMFPIs) are standard for portal imaging but have low detective quantum efficiency (DQE) at radiotherapy energies.
• Improving DQE is crucial for volumetric imaging techniques like megavoltage cone-beam computed tomography (CBCT) and cone-beam digital tomosynthesis (CBDT).

Purpose of the Study:

• To investigate the potential of thick, segmented scintillators to enhance DQE in electronic portal imaging devices (EPIDs).
• To evaluate the performance of prototype EPIDs utilizing BGO and CsI:Tl segmented scintillators for radiotherapy imaging applications.

Main Methods:

• Evaluated newly constructed segmented BGO (11.3 mm) and CsI:Tl (11.4, 25.6, 40.0 mm) scintillators using a 6 MV photon beam.
• Assessed X-ray sensitivity, modulation transfer function, noise power spectrum, DQE, and phantom images using prototype EPIDs.

Main Results:

• Prototype EPIDs showed a 12 to 25-fold improvement in DQE compared to conventional AMFPI-based EPIDs at zero spatial frequency.
• All prototypes demonstrated enhanced contrast resolution at extremely low doses, down to a single beam pulse.
• The BGO prototype offered comparable contrast resolution to conventional EPIDs but at 20 times less dose, with adequate spatial resolution for low-contrast objects.

Conclusions:

• Prototype EPIDs with thick, segmented BGO and CsI:Tl scintillators offer significantly improved portal imaging performance.
• These advancements allow for soft-tissue visualization using MV CBCT and CBDT at clinically practical doses, even at extremely low exposure levels.