JP2514025B2 - Multi-leaf collimator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a structure of a collimator for limiting an irradiation field of a radiation irradiation apparatus, particularly a medical apparatus.

[Prior Art and Its Problems] A radiation irradiator uses a collimator that limits the spread of a radiation beam so as to exactly cover the size of an object or site to be irradiated. Especially in medical devices, the shape of the organ or affected area to be irradiated is often complicated, and it is required not to irradiate the organs other than the affected area with particularly high radiation sensitivity as much as possible. To be done.

Usually, a collimator has two pairs of jews composed of blocks made of two opposing rectangular shields, which are arranged vertically with respect to the radiation source. The collimator having such a structure can change the size of the irradiation field, but its shape is limited to a rectangle.

On the other hand, in order to obtain a more flexible irradiation field,
A multi-leaf collimator is used. FIG. 14 is a conceptual diagram showing a jaw portion of a multi-leaf collimator. A plurality of leaves 10 made of radiation shielding material that are in close contact with each other,
It can be moved individually in parallel to the XX 'coordinate axis of the Cartesian coordinate system shown. The leaf group configured in this way is YY ′
Two groups are arranged on the left and right sides of the coordinate axis to form a jaw. The radiation source is on a ZZ 'coordinate axis (not shown) that passes through the intersection of the XX' coordinate axis and the YY 'coordinate axis and is perpendicular to the respective coordinate axes. Therefore, the beam axis of this radiation irradiation device is ZZ ′.
Overlaps the coordinate axes. X for each leaf as described above
An arbitrary irradiation field 1 can be formed by moving it along the X'coordinate axis and arranging it appropriately. A normal Jau, consisting of a block made of two rectangular shields, is often placed on the source side of the multileaf Jau's described here. However, since this is not directly related to the present invention, detailed description will be omitted.

15 and 16 are conceptual diagrams showing the shape and arrangement of the jaw portion of a multi-leaf collimator according to the prior art. The figure (a) is a side view, the figure (b) is a front view, and the figure (c) is a bottom view. S indicates the position of the radiation source. In addition, the leaf group is shown only on the right side of the YY 'coordinate axis to avoid complexity.

In FIG. 15, each leaf is rectangular in shape when viewed from the front and bottom, and trapezoidal when viewed from the side.
For the sake of convenience, the surface seen from the front of the leaf will be called the side surface, and the surface seen from the side will be called the end surface.

The sides of the two leaves facing each other are in close contact or face each other with a gap as small as possible, so that the radiation leaking from the gap is minimized. And each leaf can move parallel to the XX 'coordinate axis as indicated by arrow 4. It can take any suitable position, as shown at 10 '. In this way, the desired irradiation field 1 as shown in FIG. 14 can be formed.

It is highly desirable that the side surface and the end surface forming the irradiation field of each leaf be parallel to the direction of the radiation that is grazingly incident on each surface. 2,2 'in Fig. 15 (b)
The radiation indicated by 2 reaches the object to be illuminated without being attenuated by the leaf 10 '. On the other hand, the leaf 2'has been sufficiently attenuated by the leaf 10 'and hardly reaches the object to be irradiated. However, the radiation incident midway between 2 and 2 ', leaves
The degree of attenuation by 10 'varies from place to place, and therefore the intensity of the radiation transmitted through the leaf 10' varies from 2 to 2 '.
The weaker it gets toward This means that the radiation intensity continuously diminishes near the edge of the irradiation field, that is, a penumbra is formed. Of course, the penumbra also occurs due to the size of the radiation source, but the penumbra further increases due to the above. Further, in the case of the same figure, the radiation incident on the end face of the leaf 10 'may be scattered by the leaf and change its direction, and may go into the irradiation field. This shows the possibility of changing the radiation intensity in the irradiation field.

In order to minimize such an inconvenience, as described above, both the end surface and the side surface of the leaf must be parallel to the direction of the radiation that is grazingly incident on the surface. A surface in such a state will be expressed as the surface just looking into the radiation source S.

In the example shown in FIG. 15, the side surface of each leaf can be made so as to just look into the radiation source S, which is also indicated in the figure. However, in order to make the leaf move linearly parallel to the XX 'coordinate axis, it is not possible to make the end face exactly in the line of sight of the source, and normally when the leaf is fully closed the radiation leakage is minimized. In order to
Alternatively, it is made at a right angle to the bottom surface as shown in the figure for convenience of work.

FIG. 16 shows an example of another conventional multi-collimator that solves the above-mentioned drawbacks, in which the leaf 10 moves so as to rotate about a rotation axis 3 parallel to the YY 'coordinate axis. If the rotation axis is positioned so as to include the radiation source S, the leaf end face can always be exactly in line with the radiation source S. On the other hand, if it is attempted to just look into the radiation source S on the side surface of the leaf as in the example of FIG. 15, it should be noted that the leaves on the outer side of each leaf are placed so as to overlap with the leaves on the inner side. is there. For this reason, if any leaf is to be moved, i.e. to be rotated around the axis of rotation 3, the leaf immediately adjacent to it must be pushed up, thus making it impossible to move the individual leaves freely. is there. That is, in the collimator of the type shown in FIG. 16, it is necessary that the side surface of each leaf is perpendicular to the circuit axis 3 and the movement of each leaf does not push other leaves. Therefore, in order to move each leaf freely, it is not possible to have the side of the leaf exactly in line with the source.

As described above, the multi-leaf collimator according to the related art is excellent in freely forming the shape of the irradiation field, while leaving the drawback that the penumbra of the irradiation field edge is deteriorated on either the side surface or the end surface of the leaf. ing.

Fig. 17 shows the concept of an associative multi-leaf collimator that does not have such defects and does not deteriorate the penumbra on any surface. In this meditative collimator, every leaf
Reference numeral 10 constitutes a part of a spherical shell centered on the radiation source S, and therefore, the side surfaces and end faces of all the leaves have the radiation source S just in sight. In other words, it is facing the center of the spherical shell. Each leaf slides in a specific direction in the spherical shell and holds the shape of the irradiation field. So, figuratively speaking, its shape resembles a hole dug vertically into the earth's crust with all its edges. If such a collimator is provided, the penumbra is not deteriorated at any edge portion, and it is possible to minimize scattered radiation generated from the edge of the collimator and disturbing the radiation distribution in the radiation field.

According to the above metaphor, the shape of the leaf of such a collimator should become thinner as it approaches the North and South Pole, as indicated by the meridian drawn on the globe. And these leaves must be arranged close to or close to each other to prevent radiation leakage. It is clear that such reefs cannot move freely north and south along the crust. Therefore, this imaginative multi-leaf collimator cannot move the leaf and cannot be put to practical use.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems of the prior art, and to overcome the difficulty of the edge of the irradiation field as well as the above-mentioned multi-leaf collimator, it is possible to freely form the shape of the irradiation field. To provide a collimator.

[Outline of Invention]

In the multi-leaf collimator of the present invention, each leaf has the same axis of rotation or, generally, a straight line positioned in parallel and in the vicinity of the axis of rotation as a central axis, and has a radiation source or generally located on the axis of rotation. Has a shape that is substantially contained in the space sandwiched by the side surfaces of two cones whose vertices are turns near the radiation source on the central axis. By characterizing each leaf in this manner, unwanted radiation leaking from the interleaf gaps can be minimized and degradation such as penumbra, etc. at the field margin can be eliminated.

〔Example〕

 The present invention will be described in detail below with reference to examples.

FIG. 1 is a conceptual diagram showing the shape and arrangement of the jaw portion of the multi-leaf collimator of the first embodiment. YY ′ in the figure
The other leaf group, which is arranged facing the left side with respect to the coordinate axis, is omitted.

As shown in FIG. 2 (a) or (b), both side surfaces of each leaf 10 have a slight apex angle with the radiation source S as the apex and the rotation axis 3 passing through the radiation source S as the central axis. It is configured so as to match a part of the side surfaces 8a, 8b of two different cones. Further, it is convenient to construct the upper and lower surfaces of the leaf 10 so as to coincide with the side surfaces 9a and 9b of the two cylindrical bodies whose central axes are the above-mentioned rotation axes, as shown in FIG. 2 (b). .
(However, this is not a necessary condition.) When the leaf 10 having such a shape and arrangement is moved so as to rotate about the rotation axis 3, its both side surfaces are always the side surfaces of the two cones. Even if there is a second leaf of the same construction which is in contact with this leaf 10 and overlaps 8a and 8b, it does not become stuck by colliding with it. Moreover, if one of the side surfaces of the cone forming the side surface of the second leaf is shared with that of the first leaf, the opposite side surfaces of both leaves can be in close contact with each other, and Undesired leaks can be minimized.

In this way, the side surface of the leaf 10 is the source S
It is obvious that the leaf can be just projected, and if the end face of the leaf is configured to just see the radiation source at an arbitrary position of the leaf, the movement of the leaf is a rotation around the radiation source S. If you think about it, no matter where the leaf is,
It is clear that the end face just looks into the source S. Therefore, the multi-leaf collimator composed of such leaves can freely move the leaf to set the irradiation field arbitrarily, and the deterioration of penumbra etc. on the edge of the irradiation field is caused on both the side surface and the end surface of the leaf. Will be resolved. Furthermore, when the collimator is fully closed, the respective leaf end faces coincide with the end faces of the pair of leaves which are arranged facing to the left with respect to the YY 'coordinate axis, which is not shown in FIG. 1, and the radiation there is undesired. Leakage can be minimized.

The shape of one of the above leaves is shown in FIG. The same figure (a) is a side view, (b) is a front view, (c) is a bottom view. As described above, the curved surface forming the side surface of the leaf 10 has a half-vertical angle with the rotation axis 3 as the central axis and the radiation source S as the apex.
It is the side of the 90 ° -cone. As shown in FIG. 1 (a), the value of becomes larger as the leaf is farther from the ZZ 'axis, that is, the beam axis 5 of the radiation.

The angle that the maximum irradiation field makes with the radiation source S is usually about 20 °. Each of the leaves arranged to face each other occupies about half of the maximum irradiation field. Therefore, Fig. 3 (b)
The value of the angle θ shown in should be about 10 ° originally, but it is necessary to connect it with the mechanism that holds the leaf outside the maximum irradiation field and moves and fixes it. Doubled, that is, selected at 20 ° to 30 °.

The two facing sides of two adjacent leaves do not interfere with each other even if they are geometrically brought into close contact with each other. However, if the two surfaces are not actually in contact with each other, the power required to move the leaf is large. Therefore, it is preferable to dispose a space so that both surfaces do not contact with each other. This gap should be chosen so that the radiation that escapes from it does not exceed the allowable dose. According to Japanese Industrial Standard Z4705-1985 "Electronic Medical Accelerator", the absorbed dose at the rated treatment distance in the area shielded by the X-ray variable diaphragm device is the utilization line measured at the rated treatment distance on the beam axis. It is stipulated not to exceed 2% of the absorbed dose by the cone.

As a result of calculation assuming general numerical values such as related dimensions, leakage occurs when the gap between leaves is 0.4 mm X
The value of the line was 0.014 times the used line cone. Compared to the above specifications, the above value of 0.4 mm is considered as a measure of the permissible interleaf gap. This value is the second
Is effectively used in the embodiment of.

On the other hand, the first embodiment described above is ideal, and the interleaf gap can be geometrically reduced to zero. Therefore, the side surface of the cone having the rotation axis 3 as the center line and the radiation source S as the apex is referred to as an ideal space for the sake of convenience, and the space surrounded by the two ideal curved surfaces.

FIG. 4 is a sectional view showing a specific example of the above-mentioned multi-leaf collimator mounted on the irradiation head of the medical electronic accelerator. This multi-leaf collimator shows the form used for X-rays.

The electrons accelerated by the electron accelerator are converted into X-rays by a target (not shown) located at the position indicated by S, the first collimator 20, the transmission type ionization chamber 21 which is a dose monitor, the irradiation. After passing through the field indicating mirror 22, the upper movable collimator 23 and the multi-leaf collimator 10 are entered, the irradiation field is determined by these, and an irradiation target (not shown) is irradiated.

Hereinafter, the part of the multi-leaf collimator will be described in detail. Leaf 10 is a support bracket fixed to the irradiation head
The lower part is supported by the roller 12 attached to 11,
The upper part is supported by rails (not shown). The leaves are movable with respect to these supports so as to rotate about an axis of rotation 3 passing through a source S not shown. On the other hand, the side surface of the leaf of the slip is made so as to just look into the radiation source S. The leaf 10 is connected to the motor 15 and a pulley 16 mounted on its shaft by means of steel or micro chains 14. The steel or micro chain 14 is held by the idler 13 as appropriate. Thus, by rotating the motor 15 to the left or right, the leaf 10 moves to the support, to the right or left, to rotate about the axis of rotation 3.

Since all the leaves are mounted as described above, by rotating the respective motors appropriately, the leaves can be moved to the desired position to form the field.

In X-ray collimators, the leaves are often made of tungsten. Although it is possible to finish the tungsten leaf surface into a curved surface, the tendency that the leaf surface becomes expensive is inevitable because the side surfaces of each leaf are all different curved surfaces. It is possible to divide the leaves into several groups and form all the sides of the leaves in the same group to the same shape, which is one way to reduce the production cost even slightly, but reduce the price below. A second embodiment according to another method aimed at will be described.

FIG. 5 shows the structure of the leaf and the leaf frame in the second embodiment. FIG. 5 (a) is a front view, (b) is a bottom view,
(C) is a sectional view. The leaf frame 17 is made of, for example, steel having high mechanical strength and excellent workability, and its side surface is finished to have an ideal curved surface like the leaf side surface of the first embodiment.
However, this is not a requirement, and in general
Any shape may be used as long as the leaf frame 17 is included in the ideal space. The leaf 10 is attached and fixed to the leaf frame 17 by a screw (not shown) or any other suitable method. frame
The holes 18 formed in the holes 17 may be fitted with a plate made of a shielding material such as lead, if necessary, or may not be drilled if not necessary. The protrusion on the upper portion of the leaf frame 17 shown in FIG. 5 (c) is a support that is fitted into a rail (not shown) described with reference to FIG. 4 to support the leaf frame and guide it along the rail. The lower end of the frame is a surface supported by the roller 12 shown in FIG.

FIG. 6 shows the shape of the leaf in the second embodiment, (a) of which is a front view, (b) is a side view and (c) is a bottom view. The angle θ indicating the length of the leaf may in principle be sufficient to cover half the maximum irradiation field. Normally, each leaf is designed to be able to move about 3 ° beyond the beam axis, so the value of θ is about 15 °.

The feature of this embodiment is on the side surface of the leaf, which is finished to be flat. And both side surfaces thereof are included in both side surfaces of the leaf frame 17, that is, not to protrude into the ideal space, and are finished to a thickness such that the leaf side surfaces can be as close as possible to the corresponding ideal curved surface. . Specifically, when this leaf 10 is attached to the leaf frame 17,
Two lines of intersection, that is, an edge formed between the side surface of the leaf closer to the beam axis and both end surfaces of the leaf are aligned with the side surface of the leaf frame 17. That is, both edges are included in the ideal curved surface. On the other hand, an imaginary straight line drawn up and down, that is, toward the radiation source at the center of the side opposite to the above, that is, far from the beam axis, is made to coincide with the side of the leaf frame on the same side. The thickness of the leaf 10 must therefore be chosen so that the above can be achieved. The leaf group thus configured inevitably causes a gap between adjacent leaves. Obviously, this gap increases with the length of the leaf.
Also, if the leaf thickness is thicker than the above, the leaves cannot move out of the ideal space, and if it is thin, the interleaf gap becomes unnecessarily large.

FIG. 7 is a perspective view exaggerated for easy understanding of the relationship between the leaf 10 and the leaf frame 17 described above. The chain line 6 is a straight line drawn vertically in the center of the side surface of the leaf.

Now, the maximum irradiation field at a position 1000 mm away from the source S
360 × 360 mm ² , converted to the same position, each leaf can move 50 mm beyond the beam axis. The bottom edge of the leaf is assumed to be 500 mm away from the radiation source. Under this condition, the gap between adjacent leaves in the second embodiment is 0.57 mm at the outermost leaf. The size of this gap becomes smaller toward the inner leaf, and even if the inner leaf sides face each other across the beam axis, the ideal curved surface becomes the side of a cone with a half-vertical angle of 90 °, that is, the plane, so the gap is zero. become. Therefore, the above-mentioned gap obtained by averaging all fields of view is 0.
The value is close to 1/2 of 57 mm. As described in the first embodiment, the guideline for the allowable value of the interleaf gap is 0.4 mm. Therefore, the interleaf gap according to the second embodiment described above can be sufficiently tolerated.

Further, FIG. 8 is a conceptual diagram showing another method of arranging leaves. Unlike the case of FIG. 1, all the leaves are arranged at equal intervals with the radiation source S, that is, the lower end or the upper end of the leaves are aligned with a spherical surface centered on the radiation source S. When arranged in this way, the leaves according to the second embodiment may not only have flat side surfaces, but also all the leaves may have the same shape. This indicates that the leaf according to the second embodiment can be economically produced.

FIG. 9 shows still another third embodiment. In this embodiment, the leaf 10 in the second embodiment is used.
Is divided into two small leaves 10 ″. That is, in the second embodiment, the value of θ in FIG. 6 is selected to be 13 °. In the third embodiment, this value is selected to be 6.5 ° and the small leaf 10 is selected. ″ Is made and two small leaves 10 ″ are attached to the leaf frame 17 of the embodiment of FIG. 2. The advantage of splitting the leaf in this way is to bring the side of the leaf closer to the ideal curved surface. This means that the gap between the leaves is made small, and the radiation leaking from the gap can be reduced to a minimum.If the third embodiment is designed under the same conditions as the second embodiment, the maximum The inter-leaf gap on the outer side is 0.14 mm, which is a significant effect as compared with 0.57 mm of the second embodiment.

In such a configuration, the sides of the two small leaves 10 ″ are arranged at a slight angle with respect to each other, and this angle is larger for the leaves that are more outward from the beam axis. 3 is an enlarged view showing a preferred shape of the end face of the small leaf in the example. As shown, both end faces of the small leaf 10 ″ are finished as a cylindrical surface having a central axis in the height direction. Further, one of both end faces is finished to be convex and the other end is made to be concave, and their radii are formed to be equal. With such a shape, the two small leaves 10 ″ can be arranged so that their end faces are in close contact with each other, and the two small leaves 10 ″ are arranged so that each side surface has an arbitrary angle. it can. Therefore, all the small leaves in this embodiment can have the same shape and can be economically produced.

In the second and third embodiments described above, the production can be improved by flattening the side surface of the leaf or the small leaf, while the interleaf gap is slightly increased. As described above, the gap is practically acceptable, but it is preferable that as little radiation as possible leaks from the gap.

FIG. 10 is a view showing a shape of a leaf or a small leaf according to the fourth embodiment which solves the above problem, and FIG. 11 shows that the leaves are combined to make the interleaf gap substantially zero. It is the expanded sectional view shown. According to this embodiment, a groove 19 is formed on the side surface of the leaf or the small leaf, and the groove on each side surface of the two facing leaves is exactly one groove without the other groove, that is, the convex portion is fitted. The leaves are prevented from rotating around the rotating shaft 3 and colliding with each other. Under such conditions, the edge of the groove is geometrically or ideally a leaf side surface attached to the rotary shaft 3 at a regular position, and a cylindrical side surface having the rotary shaft 3 as a central axis. It is a line of intersection with, or part of an ellipse. Similarly, it is appropriate that the bottom surface of the groove 19 is a part of a plane perpendicular to the rotation axis 3. As shown in Fig. 11, the groove and the convex portion are nested in each other, and the interleaf gap is bent, and the radiation passing therethrough is scattered at the bent portion and then passes through the gap. Or it will penetrate through the substance of the leaf and the leakage will be greatly reduced. In other words, it is practically close to the gap reaching zero.

A case where the fourth embodiment is applied to the second embodiment will be specifically described. In the second example, the gap between the leaves, that is, the deviation of the leaf side surface from the ideal curved surface was 0.57 mm at the maximum. Therefore, the thickness of the leaf is set equal to the thickness of the leaf frame, that is, the thickness of the ideal space, and the depth of the deepest part of the groove is set to 0.6 mm. As a method of attaching the leaf to the leaf frame, either the leaf end portion or the central portion may be aligned with the side surface of the leaf frame. The leaf frame and the leaf thus produced shall be assembled with a gap of 0.1 mm as in the first embodiment. In the collimator assembled in this way, most of the grooves and protrusions on the facing leaf sides are nested,
Radiation leakage through the gap is significantly smaller.

In the multi-leaf collimator made in this way, it is clear that a part of the leaf protrudes slightly from the ideal space. However, the portion on the side surface of the adjacent leaf where the protruding portions face each other is a groove, and the substantial portions of the leaves do not collide with each other, which is substantially equivalent to the leaves being inside the ideal space.

On the other hand, it is feared that the unevenness on the side surface of the leaf may affect the penumbra of the edge of the irradiation field. However, since the penumbra caused by the size of the radiation source S is usually 5 to 6 mm and the unevenness is as small as 0.6 mm, deterioration of the penumbra due to the unevenness can be ignored, if any. it can.

In the above description, the edges of the groove are elliptical, but can be approximated to a circle by slightly increasing the width of the groove. Further, when the length of the leaf is short, it is possible to approximate the shape of the groove to a straight line. Further, although it has been described that the bottom surface of the groove and the both sides of the leaf are not parallel to each other, it is of course possible to make them parallel by slightly increasing the depth of the groove.

The fourth embodiment described above can be applied not only to the second and third embodiments, but also to the first embodiment. In this case, it is possible to expect an effect that a large inter-leaf gap does not cause a problem even if assembly accuracy is deteriorated.

FIG. 12 is a conceptual diagram showing the leaf array of the fifth embodiment, which is another method having the same effect as that of the fourth embodiment. The feature of this embodiment is that the cones showing the ideal curved surface of each leaf have the vertices as the vertices in all the embodiments described above, but the vertices are slightly displaced from the radiation source S. There is.

FIG. 13 is a conceptual diagram for explaining the effect of the fifth embodiment to make the interleaf gap substantially zero. The leaf applied to this embodiment is similar to that described in the first to third embodiments, except for the following one point. In other words, the cone forming the ideal curved surface described above always has the radiation source S as its apex. However, the ideal curved surface in this embodiment has one or two specific points, which are different from each other in the vicinity of the radiation source S, but generally have more points as vertices.

In the arrangement of leaves described so far, which becomes the present invention,
All the interleaf gaps allow the radiation source S exactly. Therefore, all the radiation emitted from the radiation source S and incident on the interleaf gap can pass straight through the interleaf gap in parallel with the interleaf gap. In the fourth embodiment, the radiation is prevented from passing by bending the interleaf gap, but in the fifth embodiment, the radiation is slightly inclined from the traveling direction in the interleaf gap. Therefore, it blocks the passage of radiation. That is, as shown in FIG. 13, the vertices of the ideal curved surface of the two adjacent leaves 10 are selected at the point 7 on the rotation axis 3. The gap between the point 7 and the radiation source S is selected by the following consideration. That is, the radiation 2 emitted from the radiation source S, which is incident by grabbing the upper end 7 ′ of the inner leaf side face, passes through the inter-leaf gap and squeezes the lower end 7 of the outer leaf side face of the ideal curved surface. Vertex 7 is selected. In other words, the side of the leaf is slightly tilted so that it does not look into the source.

By doing so, all the radiation incident on the interleaf gap will collide with the leaf side surface,
Therefore, the radiation passing through the interleaf gap is reduced.
It is obvious that the larger the inclination of the side surface of the leaf, that is, the further the point 7 is from the radiation source S, the less the leakage radiation is,
On the other hand, in the irradiation field line, the angle of radiation incident on the side surface of the leaf also becomes large, and the degree of deterioration such as penumbra cannot be ignored. Therefore, the method of selecting the vertex 7 described above is practically appropriate.

This embodiment shown in FIG. 12 or FIG.
When applied under the conditions shown in the third embodiment, if the maximum irradiation field is covered with 12 leaves per leaf group,
When the leaf gap is selected to be 2 mm, the gap between the radiation source S and the point 7 may be 1.9 mm or slightly larger.

In FIG. 12, vertices 7 and 7 ′ are selected as objects on the left and right of the ZZ ′ coordinate axis, that is, the beam axis. This is intended to make the radiation properties on the left and right of the beam axis symmetrical, for example, the contribution of scattered radiation from the side of the leaf, and is an effective selection although it is not an indispensable condition.

It is clear that the vertex 7 is reasonably included in the rotation axis 3 in consideration of the condition for allowing the leaf to move freely. However, in practice, the gap between the radiation source S and the apex 7 may be small, so that it may be located, for example, on the ZZ 'coordinate axis or more generally anywhere. 1 or 2
It is also clear that it is not necessary to stick to each individual.

Generally speaking, this means that the apex of the ideal curved surface may be anywhere near the radiation source S, and the central axis of the ideal curved surface may not coincide with the rotation axis 3. In particular, it is necessary to keep in mind that the interleaf gap must be increased if the central axis of the ideal curved surface does not coincide with the rotation axis 3, and such a thing is carried out unless there is some other reason. do not have to.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide a multi-leaf collimator capable of setting an arbitrary irradiation field while minimizing the deterioration of penumbra and the like at the edge of the irradiation field.
Its clinical effect is great because it does not increase the unwanted radiation leaking between the leaves.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the shape and arrangement of a jaw portion of a multi-leaf collimator showing a first embodiment of the present invention, FIG. 2 is a diagram explaining the concept of the leaf of FIG. 1, and FIG. FIG. 4 is an explanatory view of one leaf in the figure, FIG. 4 is a cross-sectional view showing a specific example of a multi-leaf collimator attached to an irradiation head of a medical electronic accelerator, and FIG. 5 is a leaf of a second embodiment of the present invention. And an explanatory view showing the structure of a leaf frame, FIG. 6 is a three-sided view showing the shape of the leaf shown in FIG. 5, and FIG. 7 is a partial perspective view showing the relationship between the leaf and the leaf frame shown in FIG. FIG. 8 is a conceptual diagram showing a leaf arrangement method, FIG. 9 is a partially enlarged view of a leaf showing a third embodiment of the present invention, and FIG. 10 is a leaf shape of a fourth embodiment of the present invention. FIG. 11 is an enlarged cross-sectional view of the interleaf gap, and FIG. 12 is the leaf shape and arrangement of the fifth embodiment of the present invention. Conceptual diagram, FIG. 13 is a conceptual diagram for explaining the effect of the substantially zero interleaf gaps of Figure 12 showing,
FIG. 14 is a conceptual diagram showing the jaw portion of a multileaf collimator, FIG. 15 is a conceptual diagram showing the shape and arrangement of the jaw portion of a conventional multileaf collimator, and FIG. 16 is a jaw portion of another conventional multileaf collimator. FIG. 17 is a conceptual diagram showing the shape and arrangement of the above, and FIG. 17 is a conceptual diagram of an associative multileaf collimator. 1 ... Irradiation field, S ... Radiation source, 10 ... Leaf.

Claims (5)

(57) [Claims] 1. A multi-leaf collimator having a plurality of leaves obtained by rotating about a rotation axis and forming an irradiation field of an arbitrary shape by the leaves rotated at appropriate positions. , The rotation axis passes at least in the vicinity of the radiation source, and the respective leaves are formed on the side surfaces of two cones having different vertex angles at least in the vicinity of the radiation source and having the rotation axis as the central axis and different half apex angles. A multi-leaf collimator characterized by having a shape that is substantially contained in the sandwiched space. 2. The multi-leaf collimator according to claim 1, wherein the rotation axis passes through a radiation source position, and the apex coincides with the radiation source position. 3. The multi-leaf according to claim 1, wherein both sides of the leaf are formed flat and are attached to a leaf frame having a shape included in the space. Collimator. 4. The respective leaves have grooves on both side surfaces, and the grooves are arranged so as to be nested with the convex portions on the opposite side surfaces of the adjacent leaves. The multi-leaf collimator according to item 2. 5. The multi-leaf collimator according to claim 1, wherein the apex occupies a position different from a radiation source position.