The present application claims the benefit of, and priority to, a Chinese patent application No. 202110184691.5, entitled “MULTI-LEAF COLLIMATOR FOR RADIOTHERAPY APPARATUS AND RADIOTHERAPY APPARATUS USING THE SAME”, filed on Feb. 10, 2021, the disclosure of which is hereby expressly incorporated by reference herein in its entirety.
The present disclosure relates to a field of radiotherapy equipment, and in particular, to a multi-leaf collimator, and a radiotherapy apparatus with a corresponding collimator.
The multi-leaf collimator (MLC) is an important component of contemporary radiotherapy machines. It is installed directly under the head of the radiotherapy machine and is used for limiting the irradiation range of the radiation beam, thus forming an irregular radiation field suitable for various target area shapes, so as to realize conformal radiotherapy. In the irradiation process, the position of the leaves of a multi-leaf collimator can be adjusted, so that the radiation intensity distribution of the irradiation range may be adjusted to perform an intensity modulated radiotherapy. Compared with conventional radiotherapy, conformal radiotherapy and intensity-modulated radiotherapy can better achieve the purpose of radiotherapy, i.e. killing tumors as much as possible while protecting the surrounding normal tissues.
The collimator leaf is a basic unit of a multi-leaf collimator, which is made of a heavy metal material (e.g., tungsten alloy) with a long strip shape. The length of a leaf is determined by the largest radiation field which needs to be formed; the width is ranged from several millimeters to several centimeters, and the narrower the width, the more suitable the formed radiation field may be for the target area; the thickness is at least five half value layers of the used metal material, so that the radiation of the leaf shielding area is attenuated below 5% of original intensity. Each leaf is driven by an independent motor, and a plurality of leaves is arranged adjacently and tightly to form a leaf set.
For the design of the multi-leaf collimator and the leaves thereof, researchers have provided a plurality of different improved solutions from different aspects, and some solutions have been applied in manufacturing and use. One option is to design the arrangement mode of the leaves, ranging from conventional single-layer to double-layer or even three-layer arrangement. Another improved design is to optimize the width and the shape of leaf end projected on the isocenter plane, through modifying the conventional equal-width leaf and the straight end surface, and obtaining the optimum leaf width and end shape through the optimization method.
There are two issues that needs to be taken into special consideration with respect to the cross-sectional shape of the leaf end in a plane perpendicular to the isocenter plane and parallel to the movement direction of the leaf. When a pair of leaves are in an open state, the leaf end is in a transition area between the area where the radiation is blocked from the leaves and the open irradiation area, so the end design has an influence on the dosage of the transition area, i.e. the penumbra. A focusing design is preferably used to make the penumbra as small as possible and minimize the change thereof along with different positions of the leaf. In a case where the cross-sectional shape of the leaf end is a linear segment, in order to achieve a focusing effect, the leaf must move along a circular arc trajectory centered on the radiation source; if the leaf moves along a linear trajectory in a direction vertical to the central axis of the radiation beam, the leaf needs to rotate itself by a small angle after it reaches the designated position, to make the straight end surface tangent to the radiation beam.
Another issue related to the leaf end design is that there is always a slit when opposite leaves are closed, leading to the problem of collision and leakage radiation. If the slit is too small, the leaves are likely to collide; if the slit is too large, it will leak too much radiation and cause side effects during irradiation. For example, the minimum projection width of the leaf slit on the isocenter plane of the Varian system is 0.05 cm, while the minimum projection width of the leaf slit on the isocenter plane of the Elekta system is 0.5 cm. For the non-focused end surface, a wider gradual change area of dose is formed below the leaf end when the opposite leaves are closed. The leakage radiation caused by the leaf slit and the gradual change area of dose below the leaf end not only causes normal tissue to be subjected to unnecessary irradiation, but also increase the difficulty for modeling and dose calculation of the accelerator, which may increase the dose calculation error.
In order to overcome the defects in the prior art, the present disclosure proposes improving the multi-leaf collimator through modifying the end design of the leaf of the multi-leaf collimator. In particular, regarding the problem that the opposite leaves of an existing collimator cannot be completely closed and a slit exists between the leaves, the present disclosure proposes an apparatus to allow the opposite leaves be embedded with each other through designing the end of leaves of the multi-leaf collimator, thus improving the working performance of the multi-leaf collimator.
According to an exemplary embodiment, there is provided a multi-leaf collimator for a radiotherapy apparatus, comprising a plurality of pairs of leaves, leaves of each pair being disposed oppositely from each other. Each pair of leaves comprises a first leaf and a second leaf which are configured to move oppositely relative to each other. In a first plane perpendicular to an isocenter plane of the radiotherapy apparatus and parallel to a direction of leaf movement, the first leaf and the second leaf are capable of moving to a closed position, where end surfaces of the first leaf and the second leaf are embedded with each other at the closed position.
In one embodiment, the end surface of the first or second leaf is configured as a fold line contour composed of a plurality of recesses and a plurality of protrusions.
In one embodiment, the plurality of recesses and the plurality of protrusions of the end surface are alternately distributed.
In one embodiment, contour lines of the plurality of protrusions of the end surface of the first or second leaf are formed as an arc segment.
In one embodiment, projections of the plurality of recesses and the plurality of protrusions of the end surface in a second plane perpendicular to the isocenter plane and the direction of leaf movement are disposed longitudinally and alternately along a direction of a connection line connecting a radiation source and a center of the multi-leaf collimator.
In one embodiment, the projections of the plurality of recesses and the plurality of protrusions of the end surface in a second plane perpendicular to the isocenter plane and the direction of leaf movement are disposed in a lattice-like arrangement.
In one embodiment, an end portion of the first leaf and/or the second leaf has a first thickness in a direction of a connection line connecting a radiation source and a center of the multi-leaf collimator, a main portion other than end portion of the first leaf and/or the second leaf has a second thickness, and the first thickness is greater than the second thickness.
In one embodiment, the first thickness of the first leaf and/or the second leaf decreases to the second thickness along a length direction from the end surface to the main portion of the first leaf and/or the second leaf.
In one embodiment, an embedment depth between the end surface of the first leaf and the second leaf at the closed position can be calculated according to the distance from an embedment position to the center line of the pair of leaves. Preferably, in a case where the end surface of the first leaf and end surface of the second leaf are arc-shaped, the embedment depth between the end surfaces of the first leaf and the second leaf at the center line of the pair of leaves is twice larger than an a contour height of an arc segment of the end surface of the first leaf or the second leaf. The embedment depth may decrease towards both the top and bottom edges of the leaf, and the embedment depth at the edges is greater than zero.
According to an exemplary embodiment, provided is a radiotherapy apparatus, comprising: a multi-leaf collimator comprising a plurality of pairs of leaves, leaves of each pair being disposed oppositely from each other and comprising a first leaf and a second leaf configured to move oppositely relative to each other, wherein, in a first plane perpendicular to an isocenter plane of the radiotherapy apparatus and parallel to a direction of leaf movement, the first leaf and the second leaf are capable of moving to a closed position, and end surfaces of the first leaf and the second leaf are embedded with each other at the closed position; and a controller, which is configured to control an embedment degree of the end surfaces of the first leaf and the second leaf at the closed position, so that the first leaf and the second leaf do not collide at the closed position.
The beneficial effect of the present disclosure is that at the closed position, the opposite first leaf and the second leaf are embedded with each other in the direction of leaf movement, so that the slit between the ends of the pair of leaves occurring when the leaves are closed for the conventional collimator no longer exists. Therefore, the shielding capability against the radiation beams can be enhanced, and the leakage radiation and the dose gradual change area are reduced. Meanwhile, the degree of embedment between the leaves can be adjusted so that there will be no collision when the leaves are closed. Compared to a conventional collimator, the range of leaf adjustment is increased, and operation is easier. The problems of the collision, the leakage radiation and the dose gradual change area of the opposite leaves during the use of the multi-leaf collimator has been solved in the present disclosure, so the collimator improves conformal intensity adjustment effect, and the difficulty of modeling and planning optimization of the collimator is also reduced.
Through a more detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings, the above and other objectives, features and advantages of the embodiments of the present disclosure will become more apparent. The drawings are included to provide a further understanding of the embodiments of the present disclosure, and are incorporated in and constitute a part of the specification to explain the present disclosure, but are not intended to serve as a definition of the limits of the present disclosure. In the drawings, the same reference numeral usually represents an identical component. It should be understood that the dimensions and sizes of the components shown in the drawings are not necessarily drawn to scale, and they may be different from those used in the embodiments for implementation shown herein. Furthermore, some embodiments may combine any suitable combination of features from two or more drawings.
The exemplary embodiments according to the present disclosure will be described hereinafter in detail with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure, and it should be understood that the present disclosure is not limited by the exemplary embodiments described herein.
In one embodiment, as shown in
In the example embodiment shown in
The number of the protrusions and the recesses at the end of each leaf can be more than 2, for example, more than 4. Preferably, the number of protrusions at the end of each leaf is the same as the number of recesses. In the end design shown in
It can be seen from
When the opposite leaves are closed, the protrusions and the recesses of the leaf 1 and the leaf 2 can be respectively embedded with each other. However, in a case where the leaves are opened, the recesses at the leaf end make the thickness of the leaf that attenuation radiation thinner, resulting in an increase of the amount of radiation penetration. Therefore, in one embodiment, the thickness h1 of the leaf end portion 13 in the direction of the connection line connecting the radiation source and the center of the collimator (i.e. the short axis direction of the leaf) may be set to be greater than the thickness h2 of the leaf main body 12. For example, h1 may be approximately twice the h2 to ensure that the thickness of the leaf that attenuate radiation at the leaf end is substantially the same as the thickness of the leaf main body (e.g. about 6-10 cm) if the end portion 13 and the main body 12 are prepared with the same material (e.g. tungsten alloy). Also, as shown in
The depth of the recess of the end portion in
y=d−2(R−√{square root over (R2−(l/2−x)2)})
In a case where y derived according to the above formula is less than 0, it indicates that the embedment depth of the opposite leaves is relatively small, and there is no overlap between the end surfaces of the leaves when the leaves are closed, so the recess does not need to be set. In a case where the two circular arc end surfaces of the opposite leaves are exactly completely embedded, the embedment depth d should be equal to 2h, and it can be calculated that the recess depth at the center of the leaf (i.e. the extension length of the protrusion at the center of the leaf) is 2h, and the recess depth at the top/bottom edge of the leaf is 0. In consideration of keeping the radiation attenuation effect of the leaf as uniform as possible when the opposite leaves are closed, the embedment depth should be 2h or slightly larger than 2h. In one embodiment, the embedment depth 2h may be 1.5 cm to 4 cm, so as to ensure the shielding capacity of the opposite leaves against radiation beam when the opposite leaves are closed.
y=d−2(R−√{square root over (R2−(l/2−x)2)})
In a case where the two circular arc end surfaces of the opposite leaves are exactly completely embedded, the embedment depth d should be equal to 2h+c, wherein c is the length of the straight segment at the top edge, and this straight segment is connected to the arc segment. It can be calculated that the recess depth at the center of the leaf (i.e. the extension length of the protrusion at the center of the leaf) is 2h+c, and the recess depth at the edge of the leaf is c. In other words, the embedment depth between the opposite leaves at the center line of the leaves is twice larger than the contour height of the arc segment of the leaf end surface, which decreases to c towards the both edges of the leaf. In one embodiment, the length c of the above-mentioned straight segment may be 0.5-1.5 cm, and the embedment depth 2h+c may be 1.5 cm to 4 cm, so as to ensure that the opposite leaves maintain the shielding capacity against radiation beams within a larger adjustment range when they are closed.
Another embodiment of the present disclosure provides a radiotherapy apparatus, comprising a multi-leaf collimator of the type described above, and a controller, which may be configured to control the embedment degree of the end surfaces of the opposite first leaf and the second leaf at the closed position, so that the first leaf and the second leaf do not collide at the closed position. For example, the embedment depth between the opposite leaves may be controlled, e.g. by adjusting the size of the recess and the protrusion, and the range of leaf movement, in order to ensure that there will be no collision when the leaves are closed. By configuring the leaf end design as described above, the movement of the collimator leaf can be controlled within a large tolerance range without a direct contact between the first leaf and the second leaf, so as to ensure that the problems of the leakage radiation of the radiation and the dose gradual change area will not occur.
The basic principles of the present disclosure have been described above in connection with specific embodiments. However, it needs to be noted that merits, advantages, effects, and the like mentioned in the present disclosure are merely exemplary and not restrictive, and the merits, advantages, effects, and the like are not considered to be requisite in embodiments of the present disclosure. In addition, the specific details of the above application are only for the purpose of illustration and ease of understanding, and are not for a limiting purpose. The above details do not limit the present disclosure must be implemented with the above specific details.
In the present disclosure, words such as “including”, “comprising”, “having”, and the like are open-ended words, referring to “including but not limited to”, and may be used therewith interchangeably. The word “or” and “and” used herein refer to a word “and/or”, and may be used therewith interchangeably unless the context indicates otherwise clearly. The word “such as” used herein refers to a phrase “such as but not limited to”, and may be used therewith interchangeably.
The above is only the preferred arrangement mode of the present disclosure and is not intended to limit the present disclosure. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present disclosure shall be included in the scope of the present disclosure.
Number | Date | Country | Kind |
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CN 202110184691.5 | Feb 2021 | CN | national |