Magnetic tracking for TomoTherapy systems: gradiometer based methods to filter eddy-current magnetic fields

Area of Science:

• Medical Physics
• Biomedical Engineering
• Radiation Oncology

Background:

• TomoTherapy systems require real-time tumor tracking for precise radiation delivery.
• Eddy-current magnetic fields in TomoTherapy systems can degrade the accuracy of electromagnetic tracking systems.
• Accurate tracking is essential to minimize off-target radiation exposure.

Purpose of the Study:

• To investigate the feasibility of using magnetic field gradients for improved localization accuracy in TomoTherapy.
• To design a tracking system that accounts for eddy fields generated within the TomoTherapy bore.
• To determine the potential of magnetic tracking for real-time tumor localization during radiotherapy.

Main Methods:

• Electromagnetic models simulated magnetic fields and eddy currents within a conducting cylinder.
• A least-squares fit using the dipole equation calculated source position from simulated sensor data.
• An iterative method estimated magnetic fields at sensor centers, accounting for spatial gradients using paired uniaxial sensors in a gradiometer array.

Main Results:

• Experimental magnetic fields were 1%-10% lower than model calculations.
• A 5x5 gradiometer array achieved 2-4 times greater localization accuracy than a planar sensor array.
• Gradiometer arrays demonstrated localization accuracy within 1.3 mm over 20 cm, compared to 5 mm for single arrays.

Conclusions:

• The gradiometer method shows significant potential for accurate magnetic tracking in TomoTherapy.
• Further research with realistic sensor models and extensive numerical studies is recommended.
• Prototype development requires a thorough estimation of magnetic tracking accuracy within the TomoTherapy system.