WO2002013907A1 - Radiotherapy simulation apparatus - Google Patents

Abstract

A radiotherapy simulator comprises a radiation source, a planar digital detector, a patient support table to lie between the accelerator and the imager, and a processing means adapted to interpret the output of the imager to produce a simulated treatment outcome. The accelerator can include an aligned visible light course to assist in patient mark up. The imager is preferable of amorphous silicon. Such imagers are available as flat panel items. It is further preferred that the accelerator and the imager are mounted on opposing arms of a C-shaped support. This provides a simple form of alignment which can be rotated around the patient easily. The imager arm is preferably retractable to allow easy access.

Description

RADIOTHERAPY SIMULATION APPARATUS

The present invention relates to a radiotherapy apparatus.

In the use of radiotherapy to treat cancer and other ailments, a powerful beam of the appropriate radiation is directed at the area of the patient which is affected. This beam is apt to kill living cells in its path, hence its use against cancerous cells, and therefore it is highly desirable to ensure that the beam is correctly aimed. Failure to do so may result in the unnecessary destruction of healthy cells of the patient.

Several methods are used to check that the alignment of the beam is correct. One such method is a simulator, a low energy source combined with a visible light source. An image can be prepared which corresponds to the therapeutic dose subsequently applied on the full scale accelerator. The visible light source allows the patient to be marked up for subsequent alignment. This form of simulation is suitable for simple treatment plans but is unable to simulate modern complex plans.

Another method is the use of a so-called "portal image". This is an image produced by placing a photographic plate or electronic imaging plate beneath the patient during a brief period of irradiation. The beam is attenuated by the patient's internal organs and structures, leaving an image in the plate. This can then be checked either before complete treatment or after a dose, to ensure that the aim was correct. Portal images are however extremely difficult to interpret as the energy of the beam which is necessary to have a useful therapeutic effect is very much greater than that used for medical imaging. At these higher energies there is smaller ratio in the relative attenuation between bony and tissue structure, which results in portal images with poor contrast. Structures within the patient are difficult to discern.

Another more recent approach is the use of CT simulation. A CT (computerised tomography) scanner is used to scan the patient. From the CT dataset, a digitally reconstructed radiograph (DRR) can be constructed that will be a prediction of the portal image that would be created. The DRR can be set up to enhance the contrast obtained and accordingly avoids the difficulties inherent in the portal image. However, dedicated CT scanners have an aperture limitation which means they cannot simulate the full range of the therapeutic accelerator. Simpler CT scanners based around a simulator can in theory simulate the full therapeutic range, but require a full rotation of the gantry to acquire each CT slice. The available speed of rotation of a simulator gantry means that it is only practical to obtain about 5 slices within a reasonable time. This is sufficient to cater for simple treatment plans but is inadequate for modern 3D treatment planning or Intensity Modulated Radiation Therapy (IMRT) treatment. In addition, CT scanners do not cast an image on the patient which can be used to mark up for later realignment.

Accordingly, there remains a need to provide a practical simulator which can accurately simulate complex treatment plans.

The present invention therefore provides a radiotherapy simulator comprising a radiation source, a planar digital detector, a patient support table to lie between the accelerator and the imager, and a processing means adapted to interpret the output of the imager to produce a simulated treatment outcome. The accelerator can include an aligned visible light course to assist in patient mark-up.

The imager is preferable of amorphous silicon. Such imagers are available as flat panel items.

It is further preferred that the accelerator and the imager are mounted on opposing arms of a C-shaped support. This provides a simple form of alignment which can be rotated around the patient easily. The imager arm is preferably retractable to allow easy access.

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figure, which shows a schematic view of the system.

As shown in Figure 1 , patient 1 0 is supported on patient table 1 2 . Above the patient is disposed a radiation source 14 capable of producing low energy radiation such as is normally used in simulation. Beneath the patient table 12 lies a planar digital detector 1 6 on a suitable support arrangement 1 8. The detector 1 6 is positioned so as to lie in the path of a beam of radiation 20 that has been omitted by the source 14 and has passed through the patient 10. The output of the detector 1 6 is fed to a computing apparatus 22.

The radiation source 14 and detector 1 6 are mounted on the ends of a rotatable C-arm and can therefore be rotated in a corelated fashion around the patient, as shown in dotted lines. The two dimensional nature of the planar detector 1 6 means that a single rotational scan of the detector and the source will enable multiple slices to be reconstructed via cone beam CT methods. Cone beam reconstruction inherently has the same resolution in all directions and is therefore suited for generation of digitally reconstructed radiographs using the computing apparatus 22. However, the need for a DRR will in many cases be eliminated as the required image will be available directly from the detector, either as a by-product of the rotational scan or as a deliberate imaging action.

The reconstruction process for generation of DRR is complex and therefore dedicated hardware within the computing apparatus is likely to be beneficial in order to reduce the reconstruction time into a period which is effectively on-line. However, it is also possible to generate the image off-line for subsequent use in planning.

A source of optical light can be incorporated within radiation source 14 in order to provide one or more (preferably two or more) reference points for marking up the patient.

Accordingly, the present invention provides a simulator which is able to produce a data set suitable for use in preparation of DRR's and treatment and planning which does not require extended CT scan times. Meanwhile, as opposed to existing scanners, the simulator is sufficiently similar to a treatment apparatus as to provide a reliable simulation process.

It will of course be appreciated that many variations can be made to the above described embodiment without departing from the scope of the present invention.

Claims

1 . A radiotherapy simulator comprising a radiation source and a planar digital detector together forming a cone beam CT arrangement, a patient support table lying between the accelerator and the imager, and a processing means adapted to interpret the output of the imager as a cone beam CT image to produce a simulated treatment outcome.

2. A simulator according to claim 1 including an aligned visible light source.

3. A simulator according to claim 1 or claim 2 in which the imager is of amorphous silicon.

4. A simulator according to any preceding claim in which the accelerator and the imager are mounted on opposing arms of a C-shaped support.

5. A simulator according to claim 4 in which the imager arm is retractable.

6. A simulator substantially as described herein with reference to and/or as illustrated in the accompanying figure.