Progressive cone beam CT dose control in image-guided radiation therapy

Area of Science:

• Medical Physics
• Radiotherapy
• Image Processing

Background:

• Cone beam CT (CBCT) is crucial for image-guided radiotherapy (IGRT), but the associated imaging dose is a concern.
• Repeated CBCT scans during treatment share similar patient data, offering potential for dose reduction.
• Current static protocols do not leverage this temporal correlation for dose optimization.

Purpose of the Study:

• To propose and evaluate a progressive dose control (PDC) scheme for reducing CBCT imaging dose in IGRT.
• To utilize temporal correlations between sequential CBCT images for dose reduction.
• To maintain CBCT image quality despite reduced imaging dose.

Main Methods:

• A dynamic CBCT scan protocol was developed to gradually decrease imaging dose per fraction.
• A prior-image based nonlocal means (PINLM) module was employed to enhance CBCT image quality.
• Proof-of-principle experiments were conducted using phantom and simulated patient data.

Main Results:

• PINLM improved image quality in low-dose CBCT (0.2 mAs) using a prior image (0.4 mAs), reducing noise from 34.95 to 12.45 HU.
• Acceptable image quality was maintained in a simulated patient case with dose levels decreasing from 0.4 to 0.05 mAs over four fractions.
• An overall imaging dose reduction exceeding 60% was achieved compared to standard low-dose protocols.

Conclusions:

• The PINLM-PDC scheme effectively reduces CBCT imaging dose in IGRT.
• Temporal correlations among sequential CBCT images are leveraged for dose reduction.
• The method maintains essential image quality for effective treatment guidance.