SU-E-J-09: Performance Optimization of Thick, Segmented Scintillators for Radiotherapy Imaging

Area of Science:

• Medical Imaging Physics
• Detector Technology
• Radiological Sciences

Background:

• Thick segmented scintillators offer potential for enhanced megavoltage active matrix, flat-panel imagers (MV AMFPIs).
• Prototypes using CsI(Tl) and BGO have shown over a factor of 20 improvement in detective quantum efficiency (DQE) at zero spatial frequency.
• However, element misalignment and mis-registration to the imager array can degrade spatial resolution and limit DQE gains at higher frequencies.

Purpose of the Study:

• To investigate methods for restoring spatial resolution and DQE in MV AMFPIs with thick segmented scintillators.
• To address the challenges posed by element-to-element misalignment and mis-registration.
• To evaluate the efficacy of high-resolution active matrix, flat-panel imager (AMFPI) arrays and specialized binning techniques.

Main Methods:

• Theoretical and empirical investigation of misalignment and mis-registration effects on imaging performance.
• Determination of modulation transfer function (MTF) and DQE.
• Imaging of a phantom in a cone-beam CT geometry using a prototype BGO segmented scintillator (120x60 elements, 50 μm septa, 1016 μm pitch) coupled to a higher resolution 127-μm-pitch AMFPI array under a 6 MV photon beam.

Main Results:

• Misalignment and mis-registration significantly degrade spatial resolution, reducing DQE at non-zero spatial frequencies.
• Standard 8x8 pixel binning can correct for mis-registration in well-aligned scintillators but is affected by misalignment.
• Selective binning, focusing on interior pixels of each scintillator element, improves resolution while maintaining DQE.

Conclusions:

• High-resolution AMFPI arrays combined with selective binning enable prototype MV AMFPIs with thick segmented scintillators to achieve performance limited solely by scintillator characteristics.
• This approach overcomes resolution losses associated with misalignment and mis-registration.
• Further development can lead to improved diagnostic imaging capabilities in megavoltage applications.