WO2013107472A1

WO2013107472A1 - Radiotherapeutic apparatus

Info

Publication number: WO2013107472A1
Application number: PCT/EP2012/000248
Authority: WO
Inventors: Rui Chen; Kevin John Brown
Original assignee: Elekta Ab (Publ)
Priority date: 2012-01-20
Filing date: 2012-01-20
Publication date: 2013-07-25

Abstract

There is a need within the art of radiation therapy for improved systems and methods that enable intra-fraction motion detection with a high degree of accuracy and reliability so as to avoid or at least significantly reduce the risk of undesired damage to surrounding tissue. We therefore disclose a radiotherapy apparatus for treating a patient, incorporating an ionising treatment modality, an ionising investigative source for determining the current patient position so as to guide the ionising treatment modality, a control system for the ionising investigative source, arranged to initiate the commencement of an investigative scan on a periodic basis, and a non-ionising monitoring system that runs continuously with the ionising treatment modality and alerts the control system as to when there appears to have been movement of the patient. In this way, unnecessary ionising investigative scans can be avoided. This reduces the ionising dose that is delivered to the patient whilst still watching for movement and retaining the accuracy of an ionising investigative source such as an x-ray system, computed tomography (CT) system, cone- beam CT apparatus, and the like. The control system initiates an investigative scan after a preset period unless the monitoring system indicates no movement, or if the monitoring system indicates movement. The monitoring system can comprises an ultrasound scanning system, and/or an optical tracking system, and/or a proximity sensor such as an infra-red proximity sensor.

Description

Radiotherapeutic Apparatus

FIELD OF THE INVENTION

The present invention relates to radiotherapeutic apparatus. BACKGROUND ART

Radiotherapy is an established technique for the treatment of tumours and other disorders. It consists of the use of one or more beams of ionising radiation, directed at the tumour site, to harm the tumour and interrupt its growth processes. Such radiation is inherently apt for such use as it is able to pass through healthy tissue around the tumour, allowing the treatment to be carried out non-invasively. The obvious difficulty with this process is that the ionising radiation is also potentially harmful to the healthy tissue through which is passes, although it is less harmful to healthy cells than to tumour cells (the "therapeutic ratio").

This is alleviated by ensuring that the dose applied to healthy tissue is substantially lower than that applied to the tumour. This can be done by directing the beam towards the tumour from a number of different directions, all of which intersect with the tumour. Thus, individual regions of healthy tissue only receive a dose from the beam when in a minority of directions, whereas the tumour receives a dose from every beam direction. This can be achieved in practice by directing a large number of beams simultaneously towards the tumour site (i.e. multiple source radiotherapy) or by directing the beam from a movable source that is rotated or otherwise moved around the patient while maintaining its alignment with the tumour site (i.e. movable source radiotherapy).

CONFIRMATION COPV Multiple-source radiotherapy is often provided by a large number of fixed radioactive gamma-ray sources, focused by means of collimators, i.e. passages or channels for obtaining a beam of limited cross section, towards a defined target or treatment volume. Each of the sources provides a dose of gamma radiation which is insufficient to damage intervening tissue. However, tissue destruction occurs where the radiation beams from all radiation sources intersect or converge, causing the radiation to reach tissue-destructive levels. The point of convergence is hereinafter referred to as the "focus point". Such a radiation device is, for example, referred to and described in US 4,780,898 which shows the system sold under the name of Leksell Gamma Knife. Such devices are usually used for the head and (potentially) the upper neck and shoulder regions due to the need to fit the patient into a hemispherical aperture around which the sources are arrayed.

Movable-source radiotherapy is often provided via a linear accelerator (LINAC) which can be used to treat all regions of the body. It delivers a uniform dose of high-energy x-ray to the region of the patient's tumour. These x-rays can destroy the cancer cells while sparing the surrounding normal tissue. The LINAC is used to treat all body sites with cancer, and is thus used in external beam radiation therapy, for Stereotactic Radiosurgery and Stereotactic Body Radiotherapy. The linear accelerator uses microwave technology to accelerate electrons in a part of the accelerator called the "wave guide", then allows these electrons to collide with a heavy metal target. As a result of the collisions, high-energy x- rays are produced from the target. These high energy x-rays will be directed to the patient's tumour and shaped as they exit the machine to conform to the shape of the patient's tumour (or other shape as prescribed). The beam may be shaped either by blocks that are placed in the head of the machine or by a multileaf collimator that is incorporated into the head of the machine. The beam comes out of a part of the accelerator called a gantry, which rotates around the patient. The patient lies on a moveable treatment couch and lasers are used to make sure the patient is in the proper position. The treatment couch can move in many directions including up, down, right, left, in, out and rotationally. Radiation can be delivered to the tumour from any angle by rotating the gantry and moving the treatment couch. Stereotactic radiation surgery is a minimally invasive treatment that allows delivery of a large single dose of radiation to a specific intracranial target while sparing surrounding tissue. Unlike conventional fractionated radiation therapy, stereotactic radiation surgery does not rely on, or exploit, the therapeutic ratio. Its selective destruction depends primarily on sharply focused high-dose radiation and a steep dose gradient away from the defined target. The biological effect is irreparable cellular damage and delayed vascular occlusion within the high-dose target volume. Because a therapeutic ratio is not required, traditionally radiation resistant lesions can be treated. Because destructive doses are used, however, any normal structure included in the target volume is subject to damage.

In radiation therapy system such as in a LINAC or Leksell Gamma Knife-, the head of a patient is immobilized in a stereotactic instrument which defines the location of the treatment volume in the head. Further, the patient is secured in a patient positioning unit which moves the entire patient so as to position the treatment volume in coincidence with the focus point of the radiation unit of the radiation therapy system. Consequently, in radiation therapy systems, such as a LINAC system or a Leksell Gamma Knife® system, it is of a high importance that the positioning unit which moves the patient so as to position the treatment volume in coincidence with the focus point of the radiation unit of the system is accurate and reliable. That is, the positioning unit must be capable of positioning the treatment volume in coincidence with the focus point to a very high precision. This high precision must also be maintained over time.

It is of particular importance to ensure that the patient does not move during the delivery of the radiation therapy when conducting radiation surgery of tumors in proximity to sensitive tissue, such as in treatment of spinal tumors. Thus, when treating tumors of the spine, one must consider the different and sensitive tissue types around the spinal column including neural tissue, meningeal tissue, bone, and cartilage. For example, damage to the neural tissue caused by the radiation may lead to irreparable damages such as partial paralysis.

In the different fixation devices used today it is not possible to immobilize the patient to such an extent that motions of body parts of the patient is completely eliminated or prevented. For example, even where the patient is fixated using a face and shoulder mask there remains a possibility that a cervical vertebra may move as a result of a small motion of the head. If a spinal tumor in the cervical region is being treated, very small movements of a cervical vertebra may result in that the radiation is mainly or partly delivered to the surrounding tissue instead of to the tumor, which may result in severe damage to the surrounding tissue.

In light of this, there is a need within the art of radiation therapy for intra-fraction motion management (IFMM) systems and methods that enable detection and monitoring of very small motions of the patient and the treated body part with a high degree of accuracy and reliability during the therapy, for example, in connection with treatment of cervical spine cancer.

In the prior art, there exists a number of solutions for intra-fraction motion management (IFMM) based on, for example, X-ray imaging, optical imaging or invasive solutions. However, these prior art methods are associated with drawbacks. For example, optical imaging require extensive image processing which may lead to complex and expensive solutions. X-ray imaging also exposes the patient to radiation, which may be injurious. Invasive solutions may be uncomfortable for the patient and may also be injurious for the patient. Furthermore, the prior art systems may have problems withstanding the gamma radiation generated in, for example, a Perfexion system (a radiation therapy system provided by the applicant).

SUMMARY OF THE INVENTION

Thus, there is a need within the art of radiation therapy for improved systems and methods that enable intra-fraction motion detection with a high degree of accuracy and reliability so as to avoid or at least significantly reduce the risk of undesired damage to surrounding tissue.

The present invention therefore provides a radiotherapy apparatus for treating a patient, incorporating an ionising treatment modality, an ionising investigative source for determining the current patient position so as to guide the ionising treatment modality, a control system for the ionising investigative source, arranged to initiate the commencement of an investigative scan from time to time, and a non-ionising monitoring system that runs continuously with the ionising treatment modality and alerts the control system as to when there appears to have been movement of the patient.

In this way, unnecessary ionising investigative scans can be avoided. This reduces the ionising dose that is delivered to the patient whilst still watching for movement and retaining the accuracy of an ionising investigative source such as an x-ray system, computed tomography (CT) system, cone-beam CT apparatus, and the like.

The ionising treatment modality can comprise a linear accelerator. In a further alternative, it can comprise a plurality of gamma-ray sources each with an associated collimator, the collimators being arranged to direct the output of the individual sources to a common focal point.

A control system is preferably provided for the ionising treatment modality, which may be integrated with the control system for the ionising investigative source. The, each, or one of the control systems can be arranged to interrupt the ionising treatment modality during a scan of the patient with the ionising investigative source.

The control system(s) can, if desired, be arranged to initiate an investigative scan after a preset period unless the monitoring system indicates no movement. They are preferably arranged to initiate an investigative scan in the event that the monitoring system indicates movement.

The monitoring system can comprise an ultrasound scanning system, and/or an optical tracking system, and/or a proximity sensor such as an infra-red proximity sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which;

Figure 1 shows a side view of a linear accelerator based radiotherapy apparatus embodying the present invention;

Figure 2 shows a schematic view of the control systems for the apparatus of figure i;

Figure 3 shows a multiple-source radiotherapy apparatus embodying the present invention; and

Figure 4 shows the non-ionising sensor of figure 3 in more detail. DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows a linear accelerator-based radiotherapy apparatus supporting the present invention. A rotatable gantry 10 is provided on a wall 12 or other substantial structure within a clinic, and is rotatable around a horizontal axis 14. A linear accelerator arm 16 extends from the gantry 10 in a generally known manner, offset from the axis 14. Within the arm 16, a linear accelerator is provided together with the usual known support apparatus in order to produce a relativistic beam of electrons and deliver this to a treatment head 18. Within the treatment head 18, the electron beam is directed towards a suitable x- ray target in order to produce therapeutic x-rays. These emanate downwards along arrow 20, after being shaped by collimators 22. The beam direction 20 intersects with the horizontal axis 14 just above a patient table 24 which is supported on a controllable support 26. The support 26 allows the table 24 to be raised and lowered, tilted, rotated and translated toward and away from the gantry 10 so as to position a patient such that the region of interest within the patient is located substantially at the intersection of the horizontal axis 14 and the beam direction 20.

An imaging panel 28 is also provided on the rotatable gantry 10, diametrically opposite the treatment head 18 and supported thereby an arm 30. The flat panel sensor 28 detects the beam emitted by the treatment head 18 after attenuation by the patient, and can therefore provide an imaging function to the apparatus. This can be done in a number of ways, the simplest being for the flat panel to provide a portal image, i.e. an image formed of the therapeutic radiation after attenuation. However, portal images are generally somewhat lacking in contrast, and it may therefore be preferable to provide a radiation head 18 which is able to emit lower-energy x-rays of a diagnostic energy, typically in the kV range rather than the MV energy range. Alternatively, if such a head cannot be provided then a second lower-energy x-ray source can be provided on the gantry 10 in combination with a suitable flat panel detector, either in addition to or in replacement for the flat panel detector 28. Regardless of which option is taken, this can be used to create one or more static radiograms of the patient, or a number of such radiograms taking at different states of rotation of the gantry 10 which can then be processed by a suitable CT imaging system in order to produce a three-dimensional rendering of the patient. In current practice, a complete scan is made of the patient using diagnostic-energy (kV) radiation and the patient position is determined. The patient table 24 is then adjusted so as to place the patient in the correct position and the treatment is commenced. From time to time, such as every five minutes during the treatment, a further diagnostic image is taken using the therapeutic energy; the treatment may be temporarily suspended during this step, although some systems are able to continue the treatment uninterrupted. This can result in an additional dose to the healthy regions of the patient in cases where the therapeutic beam is used for a scan, as these are normally taken with a wide aperture so as to include the views of distinguishable areas of the patient they can be used to ascertain the patient's position. In addition, this may create a delay in treatment, as there are regular pauses during which the radiograms have to be taken and rendered via the CT imaging system.

According to the present invention, a pair of infra-red proximity sensors or optical cameras 30, 32 are supported on the patient table 24 by suitable stands 34, 36. These are held above the patient and with a view of the relevant part of the patient being treated, and are monitored regularly by a control system (not shown in figure 1). The signal from the sensors 30, 32 can be analysed to identify any change during treatment. Such a change in the image seen by the optical cameras or in any other proximity data detected by the infra red proximity sensors would indicate that the patient has moved. The absence of such a change can therefore be correlated with the absence of movement. Thus, where the sensors record no change whatsoever, it can be inferred that the patient is still in the same position and that the treatment does not need to be interrupted.

It may still be preferred to carry out an occasional check using a diagnostic x-ray system to ensure that the sensors 30, 32 are not in error, but it is to be expected that such checks need not be carried out as frequently as is necessary in the absence of any such sensor. Therefore, the appropriate control regime for the apparatus might be to carry out a scan using the diagnostic x-ray system in order to ascertain the starting position of the patient, adjust that starting position if necessary using the adjustable support 26 so that the patient on the patient table 24 is positioned correctly relative to the beam 20 and the axis rotation 14, commence treatment using the therapeutic beam whilst monitoring the patient using the sensors or cameras 30, 32 and to then interrupt the therapeutic treatment either when the sensors 30, 32 report movement of the patient or after a pre-set period has elapsed. The patient can then be re-scanned using the diagnostic x-ray beam, and their position corrected (if necessary) using the adjustable support 26. The therapeutic treatment can then be recommenced and the process repeated. It is to be expected that the predetermined period in this case will be significantly longer than the period adopted in existing contexts, such as 15 or 20 minutes as opposed to 5 minutes.

Thus, this approach has a number of distinct advantages, being that the total dose delivered to the patient is reduced and (in particular) the dose delivered to healthy regions to the patient is significantly reduced. In addition, however, the patient position can be corrected as soon as the patient moves. In existing systems, the patient may move only a few seconds into the treatment, or a few seconds after the previous diagnostic scan, which will not be picked up for a number of minutes during which the therapeutic beam will be delivered.

Figure 2 illustrates a proposed control system for the apparatus in figure 1, assuming that the diagnostic x-ray system and the therapeutic x-ray system are separately controlled. Thus, the controlled items are the radiation head 50 which is able to emit the therapeutic beam, the diagnostic x-ray system 52, and the infra red proximity sensors or optical sensors 54. A therapeutic controller 56 passes instructions to the radiation head 50 to ensure that a clinical prescription is delivered, subject to a pause signal 58 which is provided by the diagnostic controller 60. The diagnostic controller 60 receives data from the sensors 54 and from the diagnostic system 52. As and when the sensors 54 report movement of the patient, or after a predetermined period has expired, the diagnostic controller 60 sends a pause signal to the therapeutic controller 56 to interrupt the treatment, and sends a start signal 62 to the diagnostic x-ray system 52. Once data is received from the diagnostic system 52 including patient position data, this is used to control the patient table 64 in order to reposition the patient as necessary. Once that repositioning is complete, the pause signal 58 is ceased and the therapeutic controller 56 continues with the treatment prescription.

Figure 3 shows an application of the invention to a multiple-source radiotherapy device. This comprises a hemispherical treatment head 100 in which are set a large number of radioactive sources, each collimated to direct a relatively low-intensity beam towards a treatment point. At the treatment point, the combined intensity of all these beams is sufficient to have a therapeutic effect, whereas away from that treatment point only a small minority of the beams may intersect and thus the radiation intensity is correspondingly lower. In front of the treatment head 100 there is a diagnostic imaging ring 102 comprising an x-ray source and detector which can be rotated around the patient so as to perform a single slice or cone-beam CT. A patient support 104 is provided in front of the diagnostic ring 102, and allows a patient to be supported and translated into and out of the treatment head 100. Such multiple-source radiotherapy apparatus is usually used to treat the head region of a patient, thus simplifying the patient support 104 and allowing it to be shaped with a defined body area and a defined head and neck support 106. During use, the patient support 104 can be indexed into and out of the treatment head 100 withdrawing slightly as necessary in order to place the patient within the diagnostic ring 102. Once in the treatment room 102, a cone-beam CT scan can be taken, or a CT slice can be acquired followed by which the patient is indexed slightly by the patient support 104 to allow an adjacent slice to be taken if necessary.

Alternatively, the diagnostic ring 102 could be replaced by a gantry mounted to the structure 102 of fig 3 and rotatable around the patient in the same manner as the gantry of figure 1 to provide a diagnostic imaging function.

Figure 4 shows the head and neck support 106 in greater detail. This comprises a moulded head rest area 108 which is shaped to receive the human head and support it comfortably. The support 108 is of a suitable resinous or polymeric material that is transparent to the therapeutic radiation.

The head and neck support 106 assists in stabilising the position of the patient to some degree by providing a firm surface 108 which constrains the patient movement to a degree. However, this is generally insufficient for therapeutic purposes. Thus, a pair of ultrasound sensors 110, 112 are integrated within the head and neck support 106 and project through apertures 114, 116 on the surface 108. The ultrasound sensors 110, 112 can therefore contact the patient directly to provide good coupling. During treatment, the ultrasound sensors can be operated continuously as it does not deliver an ionising dose to the patient. The ultrasound system can be operated in "A-mode", which issues a "ping" signal to measure a distance to structures in front of the transducer; in this case providing the distance to the closest hard structure, e.g. the distance to the closest bone structure in front of the transducer. Alternatively, the system can use B-mode ultrasound, to provide an ultrasound image showing internal structures within the patient.I If the patient remains stationary, then the distance measure by A-mode ultrasound will remain stable, or the internal structures of a B-mode image will remain stationary within the field of view of the ultrasound detectors. Thus, the system can be controlled in the same manner as set out in figure 2, with the ultrasound detectors 110, 112 taking the place of the sensors 54. In this way, the invention allows the excess radiation dose and the time taken for radiotherapy treatment to be minimised whilst avoiding any unwanted movement of the patient and, indeed, providing earlier warning of any such movement. The above-described ultrasound system can also be used in a linac-based radiotherapy apparatus such as that shown in figure 1. The ultrasound sensors 110, 112 can be integrated into a support that is specific to a body region, or into the patient support, or provided as a separately positionable unit that can (in principle) be used during the treatment of any part of a patient. Likewise, the IR and optical sensors described in relation to figure 1 can be applied to a multiple-source radiotherapy device as described in relation to figure 3.

An alternative non-ionising monitoring system for use in both treatment modalities is an infra-red tracking system such as the Polaris Vicra system, details of which can be seen at http://www.ndiqital.com/medical/polarisfamily.php. This is an IR tracking system using IR cameras and IR emitters, typically two of each. The system tracks small IR reflectors that act as markers, and can track these in three dimensions with high accuracy.

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

Claims

Radiotherapy apparatus for treating a patient, incorporating

an ionising treatment modality,

an ionising investigative source for determining the current patient position so as to guide the ionising treatment modality,

a control system for the ionising investigative source, arranged to initiate the commencement of an investigative scan from time to time, and

a non-ionising monitoring system that runs continuously with the ionising treatment modality and alerts the control system as to when there appears to have been movement of the patient.

Radiotherapy apparatus according to claim 1 in which the ionising treatment modality comprises a linear accelerator.

Radiotherapy apparatus according to claim 1 in which the ionising treatment modality comprises a plurality of gamma-ray sources each with an associated collimator, the collimators being arranged to direct the output of the individual sources to a common focal point.

Radiotherapy apparatus according to any one of the preceding claims in which the ionising investigative source is an x-ray system.

Radiotherapy apparatus according to any one of the preceding claims in which the ionising investigative source interrupts the ionising treatment modality during a scan of the patient.

Radiotherapy apparatus according to any one of the preceding claims in which the control system is arranged to initiate an investigative scan after a preset period unless the monitoring system indicates no movement.

Radiotherapy apparatus according to any one of the preceding claims in which the control system is arranged to initiate an investigative scan in the event that the monitoring system indicates movement.

Radiotherapy apparatus according to any one of the preceding claims in which the monitoring system comprises an ultrasound scanning system.

9. Radiotherapy apparatus according to any one of the preceding claims in which the monitoring system comprises an optical tracking system.

10. Radiotherapy apparatus according to any one of the preceding claims in which the monitoring system comprises a proximity sensor.

11. Radiotherapy apparatus according to claim 10 in which the proximity sensor is an infra-red proximity sensor.