PATIENT POSITIONING AND MOVING SYSTEM FOR

RADIOTHERAPY

DESCRIPTION

The present invention relates to a system for positioning and moving a patient for radiotherapy, and in particular a system for positioning and moving a movable first platform relative to a fixed second platform.

Ideal radiotherapy requires the treatment dose to be concentrated only and exclusively within the volume of the pathology; this result currently remains an objective still not completely achieved, but towards which all the different treatment techniques tend. In this respect, to achieve the ideal objective would signify the provision of a treatment station able to determine, foresee and then nullify all those movements of the pathology (for example those due to breathing) which are beyond its capacity to adapt the cross-section of the treatment beam to the shape of the volume to be treated. Radiosurgery using linear accelerators represents one of the currently most important solutions, with the result that this type' of unit is widespread within radiotherapy departments. The classic configuration of a radiotherapy treatment unit includes the presence of an accelerator and a bed for positioning the patient; the accelerator is able to generate a beam of particles and to concentrate them at a point known as the

isocentre in addition to rotating about a horizontal axis while continuing to maintain the emission focus at the same point, known as the isocentre. In addition to this movement the bed on which the patient is positioned can be suitably positioned and orientated to prevent exposure of healthy tissues to too high radiation doses. Evolution from a radiotherapy treatment to a radiosurgery treatment requires the capacity to identify with great precision the position of the pathology to be treated, such as to enable the administered dose to be increased while concentrating it only on that part of the tissues which is to undergo the radiotherapy treatment, so preventing other tissues from being damaged by the treatment rays. To achieve this, well visible external markers are applied to the patient, including in image diagnostics, to be able to record the position prior to treatment.

From a general viewpoint the movements of the pathology can be grouped into two categories, namely random and systematic. The random movement category comprises all those movements which occur unpredictably with time and present an arbitrary extent and direction of movement. In contrast, the systematic movement category comprises all those movements for which the movement relationship can be reasonably determined, hence enabling their extent to be predicted beforehand. Systematic movements can

be generally divided into cyclic and transient. Cyclic movements are certainly the most important (for instance those associated with breathing or heartbeats) in that they induce in organs and in the pathologies associated with them important movements which cannot be ignored during radiosurgery treatment.

Of all the considerable systematic movements, breathing plays by far the most important role during treatment in that certain very widespread tumoral pathologies (of the lung, liver,, pancreas) can undergo movements even of a number of centimetres during breathing. The annulment of these movements involves the following critical steps: measurement of the instantaneous position of the tumour, calculation of its future movements, application of a control algorithm which minimizes deviations from the real position compatible with the delay times of the device and with the use of the least possible dynamic state. Finally an adequate robotized structure able to achieve the required movements is necessary. An object of the present invention is to provide a robotized positioning and movement system for a movable first platform relative to a fixed second platform which is precise, stable and of simple construction. It must also be able to compensate the movements of the patient, via suitable observation of markers positioned on the patient

close to the treatment region, by suitably modifying the position and relative orientation of the two platforms.

According to the present invention, these and further objects are attained in accordance with the accompanying independent claims.

Further characteristics of the invention are described in the dependent claims.

The characteristics and advantages of the present invention will be apparent from the following detailed description of one embodiment thereof, illustrated by way of non-limiting example in the accompanying drawings, in which:

Figure 1 is a schematic view from above showing a system for positioning and moving a movable first platform relative to a fixed second platform;

Figure 2 is a schematic side view of a system for positioning and moving a movable first platform relative to a fixed second platform;

Figure 3 is a schematic front view of a system for positioning and moving a movable first platform relative to a fixed second platform;

Figure 4 shows schematically a radiotherapy system according to the present invention;

Figure 5 is a block diagram showing the control of a radiotherapy system according to the present invention.

The system for positioning and moving a movable first platform relative to a fixed second platform, in accordance with the present invention, is a lineapode system and is of parallel linkage type. With reference to the accompanying figures, the system comprises a fixed platform 10 fixed to a reference floor or to another interface device, and a movable platform 1 1 on which the bed is positioned, or the treatment platform. The two platforms 10 and 1 1 are connected together by legs of fixed length.

A leg 12 is connected to the fixed platform 10 by a universal joint U6 connected to a carriage C6 which can move along the direction T6, and is connected to the movable platform 1 1 by a ball joint S6. The carriage C6 is fixed to the fixed platform 10 substantially in the vicinity of an angle between a longitudinal side (long) 18 and a transverse side (short) 21 . The ball joint S6 is fixed to the movable platform 1 1 substantially in the vicinity of a longitudinal central axis 22 of the movable platform 11 at a distance of about % of the side 18 from the side 21 . The leg 12 is inclined by about 45°. The direction T6 is substantially diagonal and inclined by about 45° to the axis 22. The leg 22 is fixed symmetrically likewise.

The leg 13 is connected to the fixed platform 10 by a universal joint U5 connected to a carriage C5 which can move along the direction T5, and is connected to the movable platform 1 1 by a ball joint S5. The carriage C5 is fixed to the fixed platform 10 substantially in the vicinity of an angle between the longitudinal side (long) 20 and the transverse side (short) 21 . The ball joint S5 is fixed to the movable platform 1 1 substantially in the vicinity of a longitudinal central axis 22 of the movable platform 1 1 at a distance of about % of the side 18 from the side 21 . The leg 13 is inclined by about 45°. The direction T5 is substantially diagonal and inclined by about 45° to the axis 22. A leg 14 is connected to the fixed platform 10 by a universal joint U1 connected to a carriage C1 which can move along the direction T1 , and is connected to the movable platform 1 1 by a ball joint S6. The carriage C1 is fixed to the fixed platform 10 substantially in the vicinity of the longitudinal side 18, substantially on a central transverse axis 23 of the movable platform 1 1 . The ball joint S1 is fixed to the movable platform 11 substantially in the vicinity of the side 18, substantially at a distance of ³ A of the side 18 from the side 21 .

The leg 14 is inclined by about 45°. The direction T1 is substantially parallel to the side 18. The leg 15 is fixed symmetrically likewise. The leg 15 is connected to the fixed platform 10 by a universal joint U4 connected to a carriage C4 which can move along the direction T4, and is connected to the movable platform 1 1 by a ball joint S4. The carriage C4 is fixed to the fixed platform 10 substantially in the vicinity of the longitudinal side 20, substantially on a central transverse axis 23.

The ball joint S4 is fixed to the movable platform 1 1 substantially in the vicinity of the side 20, substantially at a distance of ³ A of the side 20 from the side 21 . The leg 15 is inclined by about 45°. The direction T4 is substantially parallel to the side 20.

A leg 16 is connected to the fixed platform 10 by a universal joint U2 connected to a carriage C2 which can move along the direction T2, and is connected to the movable platform 1 1 by a ball joint S2. The carriage C2 is fixed to the fixed platform 10 substantially in the vicinity of the side 19 at a distance of 1/3 of the side 19 from the side 18. The ball joint S2 is fixed to the movable platform 1 1 substantially in the vicinity of the side 18 close to the ball joint S1 . The leg 16 is inclined by about 45°. The direction T2 is

substantially diagonal and inclined by about 45° to the axis 22.

The leg 17 is fixed symmetrically likewise.

The leg 17 is connected to the fixed platform 10 by a universal joint U3 connected to a carriage C3 which can move along the direction T3, and is connected to the movable platform 1 1 by a ball joint S3. The carriage C3 is fixed to the fixed platform 10 substantially in the vicinity of the side 19 at a distance of 1/3 of the side 19 from the side 20. The ball joint S3 is fixed to the movable platform 1 1 substantially in the vicinity of the side 20 close to the ball joint S4. The leg 17 is inclined by about 45°. The direction T3 is substantially diagonal and inclined by about 45° to the axis 22.

The carriages C1 -C6 comprise a container resting on the fixed platform 10 and containing the carriage drive motors and the associated sensors. Each leg has one end connected to one of the two platforms by a ball joint; the other end can describe a predetermined rectilinear (or curved) trajectory which is fixed relative to the remaining platform. The movement of each movable end along said trajectory enables complete control of the position and orientation of the movable platform and consequently of the bed.

In particular, the other end is connected to one of the two platforms by a ball joint or a universal joint plus a carriage.

The device falls within the category of complete positioners by being provided with all the six degrees of freedom necessary for controlling the position and orientation of the patient.

The linear degrees of freedom have ample movements in that each individual excursion can reach 80 mm; this involves angular displacements enabling the patient to be orientated by as much as 4° both clockwise and anticlockwise about all three main axes of the system in any bed position. This characteristic should be noted in that the products of the known art attain orientation angles which are usually less and within a narrow region of the working volume, typically coinciding with the central point of the working volume described by the three translations. The typical market for the described solution is as a retrofit for existing accelerators, for which it is particularly important that the device can be easily integrated into existing devices.

The first characteristic of this bed is the small vertical dimension, enabling it to be used on practically all existing accelerators; in detail, the vertical working volume of the device is between 260 and 340 mm of height. It should

also be noted that a "dead" operative mode exists in which the bed has a thickness of only 200 mm. This particular configuration, which involves a very inclined position of the six legs, does not enable the system to be used as a positioner but is particularly useful in that it avoids having to remove the device from the accelerator to implement standard treatments. This rest position is ensured by the presence of several mechanical locking devices on which the bed, without the patient loaded, is lowered by the motors. On restoring the standard operative mode the device opens to a height of 260 mm, again without the patient loaded, at which it commences its activity as an active positioner. This particular solution presents a further distinctive element compared with other commercially available solutions, which is the facility to position all the actuator elements on a single platform fixed relative to the treatment platform, i.e. the base of the robotized bed. In addition to the said facility for reducing the vertical dimension, this choice enables the dynamic performance to be increased, with consequent improvement in compensating the pathology shift, because of the reduction in the moving masses. All the main masses, i.e. motors, reduction gears, screws and control slides are in fact in a static position; this enables movements to be

made under low inertia to the benefit of the system dynamics, with consequent compensation for the shifting pathology, for equal installed power. In effect, in this solution the only parts in a non- equipotential plane are the six support legs.

The movement system effects static movement compensation at the commencement of treatment, followed by dynamic compensation during treatment. Compensation takes place by nullifying the shifts in the pathology, by imposing equal and opposite movements on the patient.

The compensation movement to be imposed on the patient can be determined in many different ways. The most simple method is to determine the motion relationship of the treatment region by a suitable statistically compiled table of coordinates, by utilizing the information originating from the optical tracking system prior to the treatment. During treatment the optical tracking system is used as a verification system for controlling the correctness of the compensation, however its signal does not directly enter the control loop as feedback, but only to halt the system in the case of poor compensation of the relative movement. Using this method only repeatable movements (breathing) can be compensated and the patient is "obliged" to repeat the

same breathing pattern during the entire treatment, for which various techniques are possible.

At a higher complexity level the movements to be imposed on the patient can be determined directly on the basis of the data originating from the optical tracking system or from another system for measuring the position of the tumoral mass (for example a brightness intensifier). By suitable algorithms and predictions, the control system determines the position, velocity and acceleration of the positioning system, for the purpose of nullifying the relative movements between the treatment beam and the region to be treated.

The invention uses a movement control technique which is of distinctly higher effectiveness than the two stated previously, in that provides for the system for measuring the position of the pathology to be used directly as the second control feedback loop.

The first loop is the closed loop between the operations and sensors which allows traditional control of the position and velocity of the robotized bed in order to follow the programmed trajectories.

The second loop is the closed loop between the control and the external optical tracking system, which enables displacements from the planned trajectories, e.g. due to

the breathing of the patient, to be compensated in real time.

The advantages of the technique used enable the tracking error to be corrected directly within the cartesian working volume with consequent drastic reduction in the importance of any system positioning inaccuracies due to machining tolerances and/or mechanical slack. They also ensure reliability of operation as in practice the invention comprises two control loops, one at internal level and one at external level.

With reference to Figures 4 and 5, the platform 10 is positioned on a base 40, on the base 1 1 a bed 41 being positioned on which a patient 42 is rested. The patient 42 is provided with markers 43 and is imaged by a video system 44. An accelerator 45 emits a treatment beam 46 onto the patient 42.

The system comprises a control system 50 with two control loops. The first control loop 51 receives data from the sensors 53 associated with the carriages C1 -C6 and feeds them to the control system 50.

A second control loop 52 receives data from the video system 44 and feeds them to the control system 50. The control system 50 provides the commands for the actuators of the carriages C1 -C6.

In the description, reference has been made to a fixed platform 10 fixed to a reference floor, and to a movable platform 1 1 on which the bed is fixed, or treatment platform. The invention is also applicable to the case in which the fixed platform 10 is fixed to a ceiling and the movable platform 1 1 supports the accelerator 45.

The system conceived in this manner is susceptible to numerous modifications and variants, all falling within the scope of the inventive concept; moreover all details can be replaced by technically equivalent elements.