FIELD OF THE INVENTION

The invention relates to field of radiation treatment and more specifically to the use of magnetic resonance imaging for radiation treatment.

BACKGROUND OF THE INVENTION

Computed tomography (CT) images and magnetic resonance imaging (MRI) images are nowadays routinely utilized in the radiation therapy (RT) planning. In order to ensure safe and effective treatment, it is important that the same patient position and orientation is used in the treatment at linear accelerator (linac) table as was used during the imaging session prior to treatment planning. To improve patient positioning, for example, a flat tabletop can be used at MRI when imaging for RT purposes instead of the regular curved MRI imaging tabletop since also the linac treatment table is flat.

MRI uses specialized detecting coils to record the MRI signals. Due to coil geometry it may not be always possible to setup the patient so that it would be similar to what is used at the linac, or alternative coil solutions need to be used. For example, diagnostic brain imaging is done using a head coil, but for radiation therapy planning purposes another coil solution needs to be used to enable using the flat tabletop and head mask needed for head fixation. Not being able to use the head coil may mean a compromise in the image quality, especially respect to geometrical accuracy and image intensity homogeneity. This may be a major disadvantage in possible MRI-only brain applications where the therapy planning for brain radiation treatment would be done solely based on MRI images.

The use of MRI coils in combination with irradiation is for example described in US 2011/0050226A1. US 2011/0050226A1 describes an RF coil used for MR imaging that is designed so that it remains in place in the field of view of an X-Ray imaging system and comprises a support board on which copper conductive traces and copper printed capacitors are carried. The attenuation of the X-Rays caused by the copper traces is visible in the radiation image but this is compensated by arranging the non-conductive material of the support board such that the attenuation of substantially the whole of the RF coil located within the field of view is substantially constant throughout the field of view. SUMMARY OF THE INVENTION

It is an object of the invention to address the above mentioned issues related to image quality and patient positioning. This object is achieved by a mock-up antenna according to claim 1. The object is also achieved by a coil system according to claim 4.

By means of the invention, normal diagnostic radiofrequency (RF) coils can be used during imaging prior to radiation treatment for the purpose to be used for radiation treatment planning. The terms radiation treatment or radiation treatment delivery in this context designate the application of a first kind of radiation (or first radiation, or therapeutic radiation) to a (part or parts of) a patient's body for therapeutic purposes, e.g. the radiation produced by a linear accelerator or any other kind of radiation producing device, that is or may be used for therapeutic purposes in nuclear medicine. In some embodiments of the invention, the first kind of radiation may also be a radio frequency radiation.

The possibility of using standard diagnostic RF coils may improve the image quality of the resulting MRI images. It is considered very important in the field of radiation treatment that the position of the patient while being on the treatment table accurately matches the position he had when the planning images were acquired. This requirement is addressed by the invention by means of the mock-up coil having an inner surface configured to be positioned towards a patient during radiation treatment delivery in a way such that it affects the patient's position and / or orientation. In other words, the inner surface has a shape substantially similar to a shape of a working magnetic resonance antenna used during the acquisition of the planning MRI. Because both the working antenna and the mock up antenna have a similar outline for the inner surface both antennas will deform and / or orient the patient in a similar way and thereby patient positioning can be done sufficiently reproducible. The mock-up (and corresponding working antenna) may be positioned in direct contact with the patient. However, there may also be non-direct contact between the patient and the (mock-up) antenna for example thermoweldable material, like e.g. a pillow may be positioned between the patient and the (mock-up) antenna. In order to accurately (re)position the patient it is desirable to fixate the (mock-up) antenna in a certain position. Therefore, the (mock-up) antenna comprises connection means configured to allow a connection between the mock up antenna and a fixation means. The fixation means is in turn configured to fixate a position of the mock-up antenna during radiotherapy. The connection means could be any location on the (mock-up) antenna suitable for connecting a fixation means to. A fixation means is not necessarily a part of the (mock-up) antenna, but could also be part of for example the MRI system and / or patient support. The fixation means could for example be a pillow, a radiation treatment mask, an indexed table with holes and / or pins to connect to the (mock-up) antenna, screws, and / or straps. To the skilled person it will be obvious that many alternatives could be available.

According to embodiments of the invention, the fixation means are part of the (mock- up) antenna. This is advantageous, because it may limit the number of loose pieces required for setting up the patient.

According to further embodiments of the invention, the mock-up antenna may have an outline and / or appearance substantially similar to an outline and / or appearance of the (corresponding) working antenna used during the acquisition of the planning magnetic resonance image. This embodiment is advantageous, because it may make it easier for the user to see which mock-up antenna matches which working antenna. In this way positioning errors by using an incorrect mock-up antenna may be prevented. Alternatively or

additionally, the mock-up antenna could be labeled such that it is easily recognizable to which working antenna it corresponds. According to other embodiments of the invention the mock-up antenna is made substantially lighter and / or smaller than the corresponding working antenna.

As described above, according to another aspect, the invention is a coil system comprising both a working antenna and a (corresponding) mock-up antenna. The mock-up antenna comprises an inner surface configured to be positioned towards the patient during radiotherapy delivery, wherein the inner surface of the mock-up antenna has a shape substantially similar to a shape of the inner surface of the working MRI antenna. Within the coil system the mock-up antenna is the same as the mock-up antenna described above. In addition to this, the coil system also comprises a working antenna. It may be advantageous for a hospital to buy a combination of a working and mock-up antenna from the same vendor, because in this way it may be easier to guarantee the similarity in shape of the inner surface. Similarly to the mock-up coil, also in the coil system the mock-up coil could comprise fixation means. The same or similar fixation means could be used in the working antenna.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 diagrammatically shows a mock-up antenna and a working antenna according to embodiments of the invention. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 diagrammatically shows a mock-up antenna 100 and a working antenna 150 according to embodiments of the invention. Prior to radiation treatment planning, the patient 125 is positioned in the MRI to acquire images that can be used for delineating a treatment target. In a fully MRI based workflow, MRI images may be acquired that can be used to create a radiation attenuation map. For these purposes the patient is positioned on top of a working antenna 150. In figure 1, only the anterior part of the antenna is shown, as in this case, this is the part of the antenna that affects patient position and orientation. In figure 1, a working 150 and mock-up antenna 100 are shown. It can be seen in figure 1 that the working antenna and the mock-up antenna have a very similar appearance. In this figure, the only difference is that the working antenna 150 comprises a functioning antenna structure configured to transmit and / or receive RF signals to / from the patient. The mock-up antenna is substantially transparent to radiation, especially to the first kind of radiation, in order to limit the effect of the mock-up antenna on the dose delivered to the patient. Substantial radio transparency can be achieved by materials like carbon fibre, glass fibre, low-density plastics, and rigid or semi-rigid foams. The reproducibility of patient positioning may be further improved by positioning the patient on top of a thermoweldable pillow 120 that has been customized to this specific patient. In addition to this, a wedge 130 may be used. The MRI images acquired by means of the working antenna will serve as an input for creating a radiation treatment plan.

In most common clinical practise radiation treatment is not performed within an MRI scanner, but cone beam CT is used for positioning instead. In order to be able to reproduce the patient position and orientation of the MRI acquisition during treatment, the mock-up antenna 100 is used. The mock-up antenna comprises an inner surface configured to be positioned towards the patient 125 in a way such that is affects a position and / or orientation of the patient during radiation treatment. The inner surface has a shape substantially similar to a shape of a working magnetic resonance antenna used during an acquisition of the planning magnetic resonance image. As the inner surface is limited to the part of the mock-up antenna that is configured to affect patient position and / or shape, the inner surface in figure 1 is limited to the area between points 115a and 115b. In the mock-up antenna the same patient specific pillow 120 is used. The mock-up antenna further comprises connection means 160 configured to allow a connection between the mock up antenna and a fixation means 170. The fixation means are configured to fixate a position of the mock-up antenna during radiotherapy. In this embodiment the fixation means 170 are connected to the patient table in order to fixate the mock-up coil to the patient table 180.

Whilst the invention has been illustrated and described in detail in the drawings and foregoing description, such illustrations and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.