Dual-scan conformal cone-beam CT for targeted image-quality improvement using dynamic collimation

Area of Science:

• Medical Imaging
• Radiation Oncology
• Image Reconstruction

Background:

• Conventional full-field Cone-Beam CT (CBCT) in radiation therapy can lead to scatter, reducing soft-tissue contrast and limiting accuracy.
• A need exists for imaging strategies that improve image quality in specific regions while retaining full-field anatomical data for patient setup.

Purpose of the Study:

• To develop and evaluate a dual-scan conformal CBCT method utilizing dynamic collimation.
• The goal is to enhance image quality within clinically relevant areas without increasing overall radiation dose.

Main Methods:

• A dual-scan protocol combining a low-dose full-field-of-view (FOV) scan with a higher-dose conformal scan was implemented.
• Dynamic collimation, shaping the X-ray field based on the target region, was simulated using multi-leaf collimators and tested physically with a kV collimator.
• Reconstruction was performed using a regularized weighted least-squares algorithm with anisotropic total-variation regularization.

Main Results:

• The dual-scan conformal CBCT method demonstrated superior image quality compared to conventional FDK reconstruction across phantom and patient data.
• Significant improvements were observed in Signal-to-Noise Ratio (SNR) and Contrast-to-Noise Ratio (CNR) for target regions.
• For instance, CNR increased from 0.514 to 1.463 in the FORBILD phantom and from 1.036 to 2.379 in the anthropomorphic head phantom.

Conclusions:

• The proposed dual-scan conformal CBCT strategy effectively improves local image quality in the target region.
• This method preserves full-FOV information and offers a practical approach for patient-specific CBCT guidance in adaptive radiotherapy.