Radiation therapy with protons and carbon ion beams has been shown to be effective. In addition it has been shown to result in less damage to tissue than conventional gamma radiation therapy.
However, radiation planning for determining the magnitude and position of a dose to be administered is based on MRI imaging or CT imaging, which may have taken place at a considerable time period before the therapy takes place. In the intervening period, the position of the tissue to be irradiated may have moved, or changed shape. This may result in the irradiation of healthy tissue and/or missing diseased tissue, which may lead to a remission.
In ion beam therapy, the patient is in general irradiated with a beam offered in a transverse direction 110 in transversal plane ZX, as schematically illustrated in FIG. 6.
It is desirable for the beam of charged particles to be applied to a patient at the same time as MRI imaging is taking place, since the position and shape of the intended target may then be accurately known in its current position.
The majority of present MRI scanners are not suitable for this because the beam would be obstructed by the cryostat. In addition, even in ‘open’ scanners such as those employing C- or H-shaped magnets, the magnetic field of the scanner will be perpendicular to the transverse direction 110 of the charged particle beam. This will deflect the beam from the intended direction.
FIGS. 7A and 7B illustrate two examples of prior art MRI equipment, with the magnetic field B illustrated in terms of lines of magnetic flux. FIG. 7A shows a patient undergoing MRI imaging in a conventional solenoidal magnet arrangement. As illustrated, if it were possible to apply a beam of charged particles to the patient in the transverse direction 110 during MRI imaging, the beam would be perpendicular to the magnetic field B produced by the MRI equipment, and so the beam would be deflected from its intended target by the magnetic field B. In such a conventional solenoidal magnet arrangement, it is not possible to access the patient due to the presence of the solenoid surrounding the region of interest of the patient. FIG. 7B shows a patient undergoing MRI imaging in a conventional open C-shaped magnet arrangement. The patient is more accessible in such a magnet arrangement. However, as illustrated, if it were possible to apply a beam of charged particles to the patient in the transverse direction 110 during MRI scanning, the beam would be perpendicular to the magnetic field B produced by the MRI equipment, and so the beam would be deflected from its intended target by the magnetic field B.
WO02/065149 describes a coil arrangement for MRI systems, in which a transverse main magnetic field is generated. The coil arrangements described in that document produce a relatively large structure. Some of the described arrangements are difficult to manufacture. Certain embodiments of the present invention provide alternative arrangements for MRI systems, in which a transverse main magnetic field is generated, which are smaller overall structures and which employ coil arrangements which are simpler to manufacture.
US 2004/0199068 describes a system where MRI imaging is used to track the position of a target volume of a patient, and to gate the provision of a particle beam to a treatment volume, so that the particle beam is activated only when the treatment volume coincides with the target volume of the patient.
U.S. Pat. No. 6,198,957 describes a combined MRI imaging and particle beam treatment apparatus. The magnetic field of the MRI system is turned off while the particle beam treatment is applied.
According to the present invention, MRI imaging at the same time as particle radiation therapy is enabled by providing an MRI system which operates with a magnetic field in a transverse direction 110 parallel to the intended direction of application of the beam of charged particles, minimising the interference of the magnetic field with the charged particle beam while allowing access to the patient.
The present invention also provides methods for operating such equipment to perform particle radiation therapy at the same time as MRI imaging.
The present invention accordingly provides apparatus and methods as set out in the appended claims.