Patient dose and image quality from mega-voltage cone beam computed tomography imaging

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Diagnostic Imaging

Background:

• Advancements in conformal radiation therapy necessitate precise patient localization.
• Mega-voltage cone-beam CT (MV-CBCT) offers in-room imaging using the therapy beam but faces challenges with image quality and radiation dose.
• Optimizing MV-CBCT is crucial for enhancing radiotherapy accuracy and patient safety.

Purpose of the Study:

• To evaluate and optimize image quality and patient radiation dose in MV-CBCT imaging.
• To determine optimal dose levels for MV-CBCT across different anatomical sites and patient thicknesses.
• To validate dose calculations from treatment planning systems (TPS) against measured doses.

Main Methods:

• Conducted dose measurements in phantoms using ionization chambers, films, and thermoluminescent dosimeters.
• Assessed image quality metrics like contrast-to-noise ratio and spatial resolution in relation to delivered dose.
• Simulated MV-CBCT dose using a treatment planning system (TPS).

Main Results:

• Clinical MV-CBCT protocols delivered 5-9 cGy minimum and 9-17 cGy maximum dose depending on anatomy.
• Low doses are adequate for visualizing high-contrast structures like bone.
• Increased dose is required for differentiating low-contrast soft tissues.
• TPS-calculated doses showed good agreement with measured values.

Conclusions:

• Established dose ranges for effective MV-CBCT imaging, balancing diagnostic needs with radiation exposure.
• Demonstrated the feasibility of incorporating MV-CBCT dose into treatment planning for comprehensive dose management.
• MV-CBCT dose optimization is achievable, improving radiotherapy localization accuracy and patient safety.