Linac-MRI Shielding via Ferromagnetic and RF Absorbing Materials
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Solution Overview
Problem
Current solutions for combining linear accelerators and magnetic resonance imaging (MRI) systems face challenges in shielding the MRI from the linac's magnetic field and RF radiation, leading to beam degradation and interference, which results in compromised radiotherapy quality and patient access issues.
Innovation Solution
The implementation of a novel shielding method using ferromagnetic materials and RF-absorbing materials to isolate the linac from the MRI's magnetic field and RF radiation, allowing the beam to pass through while minimizing attenuation and interference, using gantry and MRI bore-mounted shims for magnetic field correction and RF shielding layers that absorb or reflect radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the linac is placed near the MRI isocenter for optimal radiotherapy treatment, then the radiotherapy quality is improved, but the MRI system experiences magnetic field interference and RF radiation interference
Solution Approach 1:
A magnetic shield is introduced as an intermediary component between the linac and the MRI system. The shield is positioned to block the magnetic field from the linac's electron gun and accelerating structures from reaching the MRI's sensitive magnetic field components, thereby eliminating magnetic field interference while allowing the linac to remain in its optimal position for radiotherapy treatment
Solution Approach 2:
An RF shield is introduced as an intermediary barrier between the linac's high-power RF source and the MRI's RF receiver coils. The RF shield blocks RF radiation from the linac from reaching the MRI system, preventing RF interference while maintaining the linac's optimal position for delivering radiotherapy beams
2Object-affected harmful factors
If shielding materials are placed between the linac and MRI system, then interference is reduced, but the radiotherapy beam experiences attenuation and degradation
Solution Approach 1:
The shielding system is designed with local quality differentiation: the magnetic shield and RF shield are positioned specifically around the electron gun and accelerating structures where interference occurs, rather than placing shielding material in the beam path. This localized approach provides interference protection while maintaining beam quality through the treatment area
Solution Approach 2:
Instead of placing shielding material in the beam path (one-dimensional approach), the shields are positioned in three-dimensional space around the interfering components. The magnetic shield surrounds the electron gun and accelerating structures, while the RF shield encloses the RF source, creating protective zones that eliminate interference without blocking the radiotherapy beam
3Object-affected harmful factors
If traditional shielding approaches are used, then interference is blocked, but patient access is compromised due to positioning constraints
Solution Approach 1:
The shielding system is designed to be dynamic and adaptable rather than fixed. The magnetic shield and RF shield can be positioned and adjusted to accommodate different treatment configurations and patient positions, allowing the linac to move freely to optimal treatment positions while maintaining interference protection. This dynamic design preserves full patient access and treatment flexibility
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables simultaneous operation of linac and MRI systems without degrading the radiotherapy beam, reducing beam attenuation, and minimizing RF interference, thus improving the quality of radiotherapy and patient access.
Implementation Method 1
The implementation of a novel shielding method using ferromagnetic materials and RF-absorbing materials to isolate the linac from the MRI's magnetic field
Implementation Method 2
RF shielding layers that absorb or reflect radiation
Implementation Method 3
using gantry and MRI bore-mounted shims for magnetic field correction
Data Source
AI summary
A radiation therapy system comprises a magnetic resonance imaging (MRI) system combined with an irradiation system, which can include one or more linear accelerators (linacs) that can emit respective radiation beams suitable for radiation therapy. The MRI system includes a split magnet system, comprising first and second main magnets separated by gap. A gantry is positioned in the gap between the main MRI magnets and supports the linac(s) of the irradiation system. The gantry is rotatable independently of the MRI system and can angularly reposition the linac(s). Shielding can also be provided in the form of magnetic and/or RF shielding. Magnetic shielding can be provided for shielding the linac(s) from the magnetic field generated by the MM magnets. RF shielding can be provided for shielding the MRI system from RF radiation from the linac.