A patient set-up protocol based on partially blocked cone-beam CT

Area of Science:

• Medical Physics
• Radiotherapy Imaging
• Radiation Dosimetry

Background:

• Three-dimensional cone-beam CT (CBCT) is crucial for radiation therapy patient setup.
• Repetitive CBCT imaging delivers significant cumulative radiation dose to patients over treatment weeks.
• Current CBCT protocols assume rigid registration, not requiring full 3D data acquisition.

Purpose of the Study:

• To develop and validate a novel patient setup protocol using partially blocked CBCT.
• To significantly reduce radiation dose delivered during patient setup in radiation therapy.
• To investigate the trade-off between dose reduction and patient setup accuracy.

Main Methods:

• A partially blocked CBCT protocol was implemented using lead strips to attenuate the x-ray beam.
• Incomplete projection data were used to reconstruct select axial slices for image registration.
• Experiments were conducted on anthropomorphic phantoms using lead sheets with varying strip widths for dose reduction.

Main Results:

• Partially blocked CBCT significantly reduces patient radiation dose (up to ~11-fold reduction).
• High patient setup accuracies were achieved, with errors <1mm translation and <0.2° rotation at ~11x dose reduction.
• Image quality of reconstructed slices was improved compared to regular CBCT, with reduced scatter signals.

Conclusions:

• Partially blocked CBCT is a viable method for accurate and low-dose patient setup in radiation therapy.
• The proposed technique offers a significant dose reduction benefit without compromising setup accuracy.
• Further optimization of beam blocking can enhance dose savings while maintaining clinical precision.