Abstract:
A radiotherapy apparatus comprising a radiation source configured to radiate a radiation ray, a multi leaf collimator, including a plurality of leaves, configured to limit a radiation range of the radiation ray and a drive unit configured to move at least one of the leaves with an ultrasonic wave.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-10393 filed on Jan. 19, 2004, the entire contents of which are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates generally to a radiotherapy apparatus which treats a diseased part, such at a tumor by using a radiation ray, and relates to its multi-leaf collimator limiting a range of the radiation ray. 
   BACKGROUND 
   A multi-leaf collimator of a radiotherapy apparatus includes groups of leaves, a main material of which is heavy metal, such as tungsten, and the leaves in each group are closely adjacent. Pairs of the groups of leaves are positioned in a radiation direction of a radiation ray. The groups of each pair move in close and opposite directions, mutually. A drive unit which moves each leaf in a conventional radiotherapy apparatus includes drive gears which contacts cogs formed in edges of leaves and are connected to a motor via shafts. The drive unit is described in Japanese Patent Disclosure (Kokai) No. 2002-253686, page 3 and FIG. 12, for example. Since it is required to move each leaf in the close and opposite directions according to a range of the radiation ray, namely a diseased part to be treated, a driving mechanism is provided with respect to each leaf 
   A conventional multi-leaf collimator includes the groups, each of which has about 40 adjacent leaves with a thickness of about 3 mm. Although it is theoretically possible to approximate the radiation range to the medical treatment range by reducing thickness of the leaves and increasing number of leaves, it is actually difficult to reduce the thickness of the leaves due to the drive gears which move the leaves and the shafts which connects the drive gears and the motor. Moreover, it is also a problem that the drive unit increases in size and in weight. 
   Furthermore, backlash could occur in such a gear mechanism, and accuracy of move control of the leaf is reduced. Therefore, when the radiation range is set, positions of the leaves are shifted, it is difficult to accurately set the radiation range, and it could be a problem that the radiation ray is radiated to a normal part of a patient. The above mentioned Japanese Patent Disclosure (Kokai) No. 2002-253686 discloses a gear mechanism which avoids the backlash, however the gear mechanism increases in size. 
   SUMMARY 
   One object of the present invention is to ameliorate the above-mentioned problems. 
   According to one aspect of the present invention, there is provided a radiotherapy apparatus comprising a radiation source configured to radiate a radiation ray, a multi leaf collimator, including a plurality of leaves, configured to limit a radiation range of the radiation ray and a drive unit configured to move at least one of the leaves with an ultrasonic wave. According to another aspect of the present invention, there is provided a radiotherapy apparatus comprising a radiation source configured to radiate a radiation ray, a multi leaf collimator, including a plurality of leaves, configured to limit a radiation range of the radiation ray and means for moving at least one of the leaves with an ultrasonic wave. According to another aspect of the present invention, there is provided a method for controlling a radiotherapy apparatus comprising radiating a radiation ray, limiting a radiation range of the radiation ray with a plurality of leaves and moving at least one of the leaves with an ultrasonic wave. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the detailed description when considered in connection with the accompanying drawings. In the drawings: 
       FIG. 1  is a perspective view of a radiotherapy apparatus; 
       FIG. 2  is a side view of a collimator of the radiotherapy apparatus; 
       FIG. 3  is a side view perpendicular to  FIG. 2 ; 
       FIG. 4  is an illustration of pair of groups of the leaves in  FIG. 2  and  FIG. 3 ; 
       FIG. 5  is an illustration for explaining a radiation range formed by a collimator; 
       FIG. 6  is an illustration for explaining a main part of a drive unit for movement of leaves in the collimator; 
       FIG. 7  is an enlarged view of the drive unit in  FIG. 6 ; 
       FIG. 8  is an illustration for explaining a principle of an operation of the drive unit; and 
       FIG. 9  is an illustration for explaining an operation of the embodiment in comparison with conventional collimator. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   An embodiment of a radiotherapy apparatus is explained in detail with reference to  FIGS. 1 to 9 . 
   The radiotherapy apparatus is mainly explained with reference to  FIG. 1  which is a perspective view. 
   The radiotherapy apparatus includes a radiation unit  10  which radiates a radiation ray from a radiation source to a patient, and a bed unit  20  on which the patient P is laid and a position of the radiation range is set. 
   The radiation unit  10  includes a fixed gantry  11  which is fixed on a floor, a rotation gantry  12  which rotates and is supported by the fixed gantry  11 , a radiation head  13  which is positioned on a top part of the rotation gantry  12 , and a collimator  14  is included in the radiation head  13 . The rotation gantry  12  can be rotated through about 360 degrees around a horizontal rotation center axis H of the fixed gantry  11 , and the collimator  14  can be also rotated around radiation axis I. An intersection of the rotation center axis H and the radiation axis I is called as an isocentre IC. The rotation gantry  12  stops when a fixed radiation method is performed or rotates when several radiation methods, such as a rotation radiation method, a pendulum radiation method, or an intermittent radiation method is performed. 
   The bed unit  20  is positioned on the floor and rotates within a predetermined angle range in a G-arrow direction along a circular arc around the isocentre IC. A top plate  22  on which the patient is laid is supported by an upper mechanism  21  of the bed unit  20 . The upper mechanism  21  moves the top plate  22  in a forward and backward direction shown as Arrow e and in a right and left direction shown as Arrow f. 
   The upper mechanism  21  is supported by a lift mechanism  23 . The lift mechanism  23  includes a link mechanism, for example, when the link mechanism goes up and down in a direction shown as Arrow d, the upper mechanism  21  and the top plate  22  move in the up and down direction in a predetermined range. The lift mechanism  23  is supported by a lower mechanism  24 . The lower mechanism  24  includes a rotation mechanism which rotates the lift mechanism  23  in a direction shown as Arrow F centering on a center at a distance L from the isocentre IC. That is, the upper mechanism  21  and the top plate  22  with the lift mechanism  23  can move in the direction shown as Arrow F in a predetermined range. 
   A positioning of the patient P to be treated and a setting of the radiation range of the collimator  14  are performed a staff D, such as a doctor. 
   When the radiation treatment is performed, it is desired that the radiation ray is radiated only to a diseased part, such as a tumor and that a normal tissue is not damaged. Therefore, in order to reduce the radiation ray radiated to the normal part, the collimator  14  which limits the radiation range is provided in the radiation head  13  as the collimator  14  can rotate around the radiation axis I. 
   The collimator  14  is shown in  FIGS. 2 to 4 , and is explained in detail.  FIGS. 2 and 3  are illustrations for explaining a first pair of the leaves and a second pair of groups of leaves and are perpendicular, mutually.  FIG. 4  is a flat view indicating the second pair of leaves. 
   The collimator  14  includes the first pair  140  of leaves mainly made of heavy metal, such as tungsten, and the second pair  141  of leaves, and the first and second pairs are arranged along a radiation direction of the radiation ray radiated from a radiation source S. As shown in  FIGS. 2 and 3 , the pairs  140  and  141  are divided into two groups  140 A and  140 B, and  141 A and  141 B, respectively. 
   The first leaves  140 A and  140 B which are close to the radiation source S work as a single component, and move in a direction shown as Arrow X along an arc-shaped plane centering on the radiation source S. Each group is moved closer and farther, mutually, by first drive units I  42 A and  1   42 B which transfer mechanical powers to the leaves from the motor via the gear mechanisms. 
   The second groups  141 A and  141 B of leaves which is far from the radiation source S, as shown in  FIG. 3 , mutually move closer and farther, in a direction shown as Arrow Y which is along an arc-shaped plane centering on the radiation source S and which is perpendicular to the direction of the movement of the first leaves  140 A and  140 B. The second groups  141 A and  141 B of leaves, as shown in  FIG. 2  and  FIG. 4 , includes a plurality of leaves  141 A 1  to  141 An and  141 B 1  to  141 Bn, and the leaves  141 A 1  to  141 An and  141 B 1  to  141 Bn are adjacent, respectively. The leaves  141 A 1  to  141 An and  141 B 1  to  141 Bn are mainly made of heavy metal. 
   The leaves  141 A 1  to l 4 lAn and  141 B 1  to l 4 lBn of the second groups  141 A and  141 B are moved in the arc-shaped plane by second drive units. The second drive units include stators STA 1  to STAn and STB 1  to STBn which are attached to edges of the leaves, signal lines LA 1  to LAn and LB 1  to LBn connected with the stators and a high-voltage generation units GA 1  to GAn and GB 1  to GBn which supply high-voltage to the stators via the signal lines. In this embodiment, an operation of the second drive units and  113 B 1  to  113 Bn which move the leaves  141 A 1  to  141 An and  141 B 1  to  141 Bn of the second groups  141 A and  141 B is different from an operation of the first drive units  142 A and  142 B which move the first leaves  140 A and  140 B. Switch circuits which are connected to the second drive units select the leaf to be moved among the second groups of leaves. 
   By a combination of the close and far movement of the first leaves  140 A and  140 B in the X direction and the close and far movement of the second groups of leaves  141 A and  141 B in the Y direction, an irregular radiation range U which is approximated to a diseased part T can be created, as shown in  FIG. 5 . 
   The second drive units which move the leaves  141 A 1  to  141 An and  141 B 1  to  141 Bn of the second groups  141 A and  141 B. 
     FIG. 6  shows an illustration for explaining the second drive units which move the leaves  141 A 1  and  141 B 1 . The edges of the leaves  141 A 1  and  141 B 1  strongly contact the stators STA 1  and STB 1  with contact pressure. The stators STA 1  and STB 1  include metal materials M, elastic bodies EL and piezoelectric transducers CE. The piezoelectric transducer CE is known as an ultrasonic transducer, such as piezoelectric ceramic, which generates ultrasound according to received high frequency electric signal. The piezoelectric transducers CE are connected to the high-voltage generation units GA 1  and GB 1  via the signal lines LA 1  and LB 1 , and high frequency electric signals are supplied to the piezoelectric transducers. 
   With reference to  FIG. 7 , the leaf  141  and the drive unit  143  are explained. The second drive units and the leaves  141 A 1  to  141 An and  141 B 1  to  141 Bn are the same as or similar to the following drive unit  143  and the leaf  141 . 
   The stator ST which strongly contacts the edge of the leaf  141  with the contact pressure is first explained. 
   The stator ST, as a single unit, includes a piezoelectric transducer CE, a metal material M and an elastic body EL positioned therebetween, and a surface of the metal material M directly contacts the edge of the leaf  141 . Furthermore, a plurality of comb-shaped grooves t are created on a contact side of the metal material to the leaf  141 , and the groove extends in a direction perpendicular to a width direction of the leaf  141 . Each piezoelectric transducer includes an electrode, and the high frequency electric signal is supplied from the high-voltage generation unit G to the electrode via the signal line L. 
   An operation of the drive unit is explained with reference to  FIG. 8 . In  FIG. 8 , the same reference numbers are attached as illustrated in  FIG. 7 . 
   When the predetermined high frequency voltage of the high frequency signal is supplied from the high-voltage generation unit G to the piezoelectric transducer CE, an ultrasonic vibration is generated in the piezoelectric transducer CE. This generated ultrasonic vibration proceeds in one direction continuously, bending a metal material M of the stator ST. That is, as if a wave of a sea wimples in one direction, the ultrasonic vibration generated in the piezoelectric transducer CE bends the stator ST. 
   Therefore, a plane, which contacts the stator ST, of the leaf  141  includes a portion where a head of the wave contacts and another portion where the head does not contact. On the head (peak) of the wave which contacts the plane of the leaf  141 , elliptic movement occurs on the contacting point, a track of the elliptic movement is drawn in an opposite direction to a movement direction of the wave proceeding on the stator ST, and a long axis of the elliptic movement is different from the movement direction of the wave. Therefore, in response to influence of the elliptic movement, the leaf  141  moves in an opposite direction to the movement direction of the wave proceeding on the stator ST. 
   Therefore, when the stator ST is fixed, the leaf  141  is movable and the wave occurs on the stator ST in a right direction, the elliptic movement occurs in a left direction on each peak which contacts the leaf  141 . In response to the elliptic movement, the leaf  141  moves in the left direction to the stator ST. On the other hand, when the wave proceeds in the left direction on the stator ST, the leaf  141  moves in the right direction. Thus, by controlling the high frequency signal supplied to the piezoelectric transducer CE of the stator ST, it is possible to move the leaf  141  in an arbitrary direction. 
   The plurality of comb-shaped grooves t are provided on a side, which contacts the leaf  141 , of the metal material M of the stator ST, in order to enlarge amplitude of the elliptic movement and reduce friction 
   The present invention may be not limited to the above embodiments, and various modifications may be made without departing from the spirit or scope of the general inventive concept. For example, although it is explained in the above embodiment that the outside surface of the leaf  141  contacts the stator ST, an inside surface of the leaf  141  may contact the stator ST to move the leaf  141 . 
   As explained above, according to the embodiment, the following various effects, which does not limit the present invention, are considered, for example. 
   In a first effect, when the leaf is moved directly by the stator which mainly includes the piezoelectric transducer, a driving mechanism can be simplified and miniaturized. Therefore, it is possible to reduce the thickness of each leaf and increase the number of leaves, and the irradiation range of radiation can be approximated to the medical treatment range more. 
   In a case where the collimator  14  is the same size, radiation ranges, about the second groups of leaves  141 A and  141 B, formed by conventional small number of thick leaves and by large number of thin leaves in the embodiment are illustrated in  FIGS. 9A and 9B , respectively. In  FIG. 9A  showing the conventional small number of thick leaves, large gaps (unnecessary radiation range) occur even when the radiation range is approximated to a shape of diseased part F as much as possible. In  FIG. 9B  showing the large number of thin leaves in the embodiment, since the radiation range is approximated to the shape of the diseased part F more, the unnecessary radiation range can be reduced. 
   In a second effect, since a gear mechanism is not used to move the leaves, the backlash does not occur, and an error of a stop position of the leaves can be reduced, and setting accuracy of the radiation range can be improved. 
   In a third effect, since speed is controllable in stepless, high accurate speed control and position control are possible, and the stop position accuracy of the leaves is improved. Moreover, since operation noise is reduced, it is suitable as a medical apparatus. 
   In a forth effect, since the leaf and the metal material of the stator are contacted in high contact pressure, even after the supply of the high frequency voltage to the piezoelectric transducer is stopped, namely power supply is stopped, a brake function which maintains holding power continues. Once the position of the leaf fixed, the position is maintained and interference between adjacent leaves is reduced, and therefore the setting accuracy of the radiation range is improved. In addition, the metal material M may be placed on farther positions from the isocentre than a maximum radiation range when the leaves  141 A 1  and  141 A 2  are positioned in furthermost positions. In this case, the metal materials do not block the radiation ray.