In the context of radiation therapy a target within a human body generally has to be irradiated in order to treat a disease for example, in particular a tumor. In this process a radiation therapy apparatus applies a high radiation dose in a targeted manner in an irradiation region (isocenter) of the human body. During irradiation the problem frequency occurs that the irradiation region moves and/or is displaced. Thus a tumor in a stomach region for example moves during an respiratory process of a patient. On the other hand a tumor can grow or reduce in size in a time interval between radiation planning and the actual irradiation.
It has therefore been proposed to monitor a position of an irradiation target in a patient during irradiation by means of medical imaging. This allows a beam and/or beam guide for irradiation to be controlled or optionally irradiation to be terminated. It is also of significant interest to track a radiation focus in respect of the actual position of the irradiation region.
A combined radiation therapy apparatus and magnetic resonance apparatus is particularly advantageous. This features high soft part resolution compared with a computed tomography apparatus for example, so that an advantageous contrast can be shown in this region.
For efficient irradiation a radiation source of the radiation therapy apparatus is positioned as close as possible to a patient. To this end the radiation source is generally disposed at least partially within the magnetic resonance apparatus and in particular within a magnetic field of the magnetic resonance apparatus. However this arrangement has the disadvantage that an electron path of electrons of an electron beam of the radiation therapy apparatus is subject to interference from the magnetic field of the magnetic resonance apparatus.
WO 03/008986 A2 proposes a separation of gradient coils of the magnetic resonance apparatus and a tailored design of a main magnet, so that an almost magnetic-field-free space is produced outside the magnetic resonance apparatus. However this arrangement has the disadvantage that the apparatus is of large extension and only one angle of incidence is available for a radiation treatment. Also the separated gradient coils result in significant disadvantages in respect of the image quality of medical imaging. Also the radiation from the radiation therapy apparatus must penetrate a steel body of the magnet, resulting in a deterioration and/or degradation of the beam profile and beam intensity.
A combined magnetic resonance apparatus and radiation therapy apparatus, in which however an x-ray and/or gamma beam is generated for the purposes of irradiation outside the magnetic resonance apparatus and therefore outside the active region of a magnetic field, is also known from U.S. Pat. No. 6,198,957 B1. This means that the x-ray beam is generated a very long distance from the actual treatment region, so the apparatus is likewise of large extension, in particular with a variation of an angle of incidence. Also the long distance means that a high radiation dose has to be generated, to achieve the required penetration depth of radiation for the radiation treatment.
A guide for an electron beam along a main axis of the magnetic resonance apparatus is also known from DE 102008007245 A1. The electron beam is deflected through 90° to collide with a target. An electron beam and the target are disposed within a patient support of the magnetic resonance apparatus. However this means that the space available for the patient within the magnetic resonance apparatus is additionally limited by the radiation therapy apparatus.