Today at the Annual Meeting of the American Association of Physicists in Medicine in Anaheim, California, researchers from the University of Alberta will present a new system for radiation oncology that combines linear accelerator and an MRI machine. The hybrid device allows live viewing of tumor tissue and precise radiation targeting of moving organs, like lungs, prostate, and maybe even the heart. The biggest problem is that the magnet is a permanent type and provides nowhere near the resolution of modern 3 Tesla superconducting ones.
More details from MIT Technology Review:
Until now, it hasn’t been possible to use MRI to guide radiotherapy. This is because MRI machines and the linear accelerators that supply high-energy x-rays for radiotherapy interfere with each other. MRI uses a strong magnet and pulses of radio-frequency waves to excite and read a signal from protons in the water molecules inside soft tissues in the body. Medical linear accelerators also use radio-frequency pulses, in their case in order to accelerate electrons through a waveguide toward a metal target. When the electrons hit the target, high-energy x-rays come out the other side; these x-rays are then aimed at tumor tissue. If these two machines are in the same room, the magnetic field from the MRI interferes with the waveguide, preventing the electrons from being accelerated, and the radio-frequency pulses from the linear accelerator interfere with the imager’s magnetic field, degrading picture quality.
To combine the technologies, the Alberta researchers had to reengineer both components. “The whole machine is designed differently,” says Fallone. Special shielding is employed. And instead of using a high-strength magnetic field generated by superconducting-wire coils, as in clinical MRI, the machine uses a weak permanent magnet. The weak magnet interferes much less with the accelerator and is smaller and less expensive to operate. This December, Fallone’s group published the results of imaging studies that showed it was possible to generate MRI images while running the linear accelerator without interference.