Fast, low-dose patient localization on TomoTherapy via topogram registration

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Guidance

Background:

• Accurate patient positioning is crucial in radiotherapy.
• Current TomoTherapy workflows often rely on 3D megavoltage computed tomography (MVCT) for localization.
• MVCT involves significant imaging time and radiation dose to the patient.

Purpose of the Study:

• To investigate an efficient protocol for TomoTherapy patient localization using scout imaging (topogram).
• To evaluate the topogram mode as a replacement for or supplement to 3D MVCT imaging.

Main Methods:

• Acquisition of topograms using the TomoTherapy MV imaging system.
• Generation of digitally reconstructed topograms (DRTs) from kV CT simulation data.
• Theoretical and experimental exploration of unique geometric characteristics.
• Performance evaluation of MV topogram system (image quality, dose, acquisition time).

Main Results:

• Clinically usable topograms acquired in 12.5 seconds (50 cm field length).
• Patient dose from topogram is less than 1% of helical MVCT dose.
• Potential for dose reduction to <25 microGy per scan with system refinements.

Conclusions:

• Topogram localization offers a fast and low-dose alternative to 3D MVCT on TomoTherapy.
• Exclusive use of MV topograms could reduce imaging time by 30-fold and dose by 100-fold.