Simultaneous reduction of radiation dose and scatter for CBCT by using collimators

Area of Science:

• Medical Physics
• Radiotherapy Imaging
• Image Reconstruction

Background:

• On-board cone-beam CT (CBCT) is crucial for radiotherapy target localization.
• Frequent CBCT use raises concerns about radiation dose and image quality due to scatter.
• Collimators offer a potential solution to reduce both dose and scatter.

Purpose of the Study:

• To investigate the impact of collimator design on CBCT image quality.
• To determine the relationship between collimator blocking ratios/patterns and image fidelity.
• To assess the feasibility of reconstructing artifact-free CBCT images with collimators.

Main Methods:

• Simulated a CBCT system with various collimator designs (slit size, number).
• Varied beam transmission ratios (100% to 10%) across hundreds of scenarios.
• Utilized lung and pelvis phantoms and an iterative reconstruction algorithm with compressed sensing.
• Evaluated image quality using Root Mean Square Errors (RMSEs).

Main Results:

• CBCT image quality improved with increased beam transmission through collimators.
• Larger collimator slit sizes degraded image quality.
• Comparable image quality to conventional CBCT was maintained until beam transmission dropped below 25% with ultra-high resolution collimators.

Conclusions:

• Collimators effectively reduce scatter and radiation dose in CBCT.
• CBCT image quality is significantly influenced by collimator blocking ratio and pattern.
• Adequate data quantity and format are essential for achieving conventional CBCT image quality with collimated systems.