JP2009261690A - Magnetic guide device and radiotherapy apparatus - Google Patents

Abstract

An object of the present invention is to detect a magnetized pattern of a magnetized medium with a magnetic sensor at a distance.
A flat soft magnetic layer containing soft magnetic particles and a flat nonmagnetic layer containing no soft magnetic particles are alternately laminated, and an exposed cross section of the laminated film is formed on a mounting surface to a magnetic sensor and a contact surface with a leaf. The magnetic guide 90 is created by cutting and processing into a suitable shape. The magnetic guide 90 is disposed between the magnetic tape 46 and the magnetic sensor 48. For the magnetic guide 90, a material composed of a columnar soft magnetic region and a non-magnetic region can also be used.
[Selection] Figure 10

Description

  The present invention relates to a technique for drawing out a magnetic field pattern generated by a magnetized medium such as a magnetic tape or a magnetic sheet to a position that can be detected by a magnetic sensor, and a radiotherapy apparatus.

  In a radiotherapy apparatus, a “multi-leaf collimator” (hereinafter abbreviated as MLC) is used to adjust a radiation irradiation region. The linear motion type MLC that moves the leaf in a straight line has a drawback that a penumbra is generated at the edge portion of the leaf. In the arc-shaped leaf, teeth are carved on the lower side surface for leaf movement and connected to a motor via a power transmission mechanism (see, for example, Patent Document 1).

  Since MLC moves each leaf independently and adjusts the radiation irradiation area with high accuracy, it is necessary to measure each leaf position independently in real time and with high accuracy (several tens of μm). In addition, since very strong radiation is irradiated, it is necessary to use a position measurement technique with excellent radiation resistance.

  Thus, for example, position measurement means such as an encoder or a potentiometer is provided in any of a plurality of transmission gears used in the power transmission mechanism, and the position of the leaf is measured by detecting the rotation of the transmission gear.

JP 2007-195652 A

  However, when the power transmission mechanism is constituted by a plurality of transmission gears, backlash occurs in each of the plurality of gears. According to the method of measuring the leaf position based on the rotation of any one of the plurality of transmission gears, an error corresponding to backlash occurs between the measured leaf position and the actual position. Therefore, an attempt is made to detect magnetic pattern information by sticking a magnetic tape magnetized at equal intervals to the concave end surface portion of each arc-shaped leaf as shown in FIG. Then, since the shape of the magnetic sensor is generally flat, a gap is inevitably generated, so that there is a problem that it cannot be detected with sufficient sensitivity.

  The present invention has been made in order to solve the above-described problems caused by the prior art, and the radiation treatment apparatus capable of accurately measuring the position of the leaf and the radiation treatment apparatus accurately measuring the position of the leaf. It is an object of the present invention to provide a magnetic guide device that can be used.

  In order to solve the above-described problems and achieve the object, the present invention according to claim 1 is configured such that flat soft magnetic layers containing soft magnetic particles and flat nonmagnetic layers containing no soft magnetic particles are alternately laminated, A magnetic guide device that draws a magnetic field pattern generated by a magnetization medium to a lamination exposure section opposite to the lamination exposure section when the lamination exposure section is brought into contact with the magnetization medium.

  According to a second aspect of the present invention, there is provided a plurality of straight columnar magnetic regions including soft magnetic particles, the central axes of which are all oriented in a certain direction and arranged two-dimensionally at equal intervals, and the columnar magnetic regions. The magnetic field pattern generated by the magnetized medium when the central axis cross section of the columnar magnetic region is brought into contact with the magnetized medium is formed of a nonmagnetic region that fills the gap. It is a magnetic guide device characterized by being drawn out in a cross section of the shaft.

  According to a sixth aspect of the present invention, there is provided a multi-leaf collimator for adjusting an irradiation region of radiation, a magnetizing medium attached to an upper end portion of each arc-shaped leaf constituting the multi-leaf collimator, and the magnetizing A magnetic sensor that detects a magnetic field pattern generated by the medium, and a magnetic guide device that is arranged between the magnetic medium and the magnetic sensor and extracts the magnetic field pattern generated by the magnetic medium so that the magnetic sensor can detect the magnetic sensor; The magnetic guide device is configured such that a flat soft magnetic layer containing soft magnetic particles and a flat nonmagnetic layer containing no soft magnetic particles are alternately laminated, and when the laminated exposed cross section is brought into contact with the magnetization medium, A radiotherapy apparatus characterized in that a magnetic field pattern generated by a magnetized medium is drawn to a layered exposed cross section opposite to the layered exposed cross section so that the magnetic sensor can detect the magnetic field pattern.

  According to a seventh aspect of the present invention, there is provided a multi-leaf collimator for adjusting a radiation irradiation region, a magnetizing medium attached to an upper end of each arc-shaped leaf constituting the multi-leaf collimator, and the magnetizing A magnetic sensor that detects a magnetic field pattern generated by the medium, and a magnetic guide device that is arranged between the magnetic medium and the magnetic sensor and extracts the magnetic field pattern generated by the magnetic medium so that the magnetic sensor can detect the magnetic sensor; The magnetic guide device includes a plurality of straight columnar magnetic regions including soft magnetic particles, all of which have a central axis directed in a certain direction and two-dimensionally arranged at equal intervals, and a non-magnetic material that fills a gap between the columnar magnetic regions. When the central axis cross section of the columnar magnetic region is brought into contact with the magnetized medium, the magnetic field pattern generated by the magnetized medium is opposite to the central axis cross section. Is radiation therapy apparatus characterized by pull the center axis cross-section the magnetic sensor is detectable.

  According to the first or second aspect of the present invention, the magnetic field sensor at a position away from the magnetic field pattern generated by the magnetized medium can be detected.

  According to this invention of Claim 6 or 7, a magnetic sensor can be arrange | positioned away from the magnetization medium.

  Exemplary embodiments of a magnetic guide device and a radiotherapy device according to the present invention will be described below in detail with reference to the accompanying drawings.

  First, the configuration of the radiotherapy apparatus according to the present embodiment will be described. FIG. 1 is a schematic diagram illustrating a configuration of a radiotherapy apparatus according to the present embodiment. The radiation therapy apparatus 1 is an apparatus for treating an affected area of a subject. The affected part is treated by generating radiation and exposing it to the affected part of the subject.

  The radiotherapy apparatus 1 includes a treatment table 2 on which a subject is placed, a rotating frame 3 that exposes radiation, and a rotating support table 4 that rotatably supports the rotating frame 3.

  The treatment table 2 is provided with a top plate 2a that can be moved in the body axis direction of the subject (in the direction of arrow A in FIG. 1), and can move up and down (in the direction of arrow B in FIG. 1). is there. The treatment table 2 can be rotated (arrow C in FIG. 1) in which the surface of the top plate 2a maintains a parallel relationship with the installation surface of the radiation treatment apparatus 1.

  The rotation support base 4 is fixed to the apparatus installation surface, and supports the rotation base 3 via a rotation shaft 4a. The rotation support 4 rotates the rotation frame 4a so that the rotation frame 3 can rotate in the direction of the axis (arrow D in FIG. 1).

  The rotary mount 3 has a three-dimensional shape with a substantially L-shaped cross section. Of the substantially L-shaped solid shape, one arm 3a is supported by the rotation support base 4, and the other one arm 3b is provided with the irradiation head 5. The irradiation head 5 is disposed to face the treatment table 2.

  The irradiation head 5 is provided with a radiation source S and exposes the radiation to the subject. The radiation source S is composed of an electron accelerator, a counter electron beam target, and the like, and generates radiation by accelerating electrons with the electron accelerator and colliding with the counter electron beam target. The generated radiation is X-rays, γ-rays, etc. In addition to this, there is a method of irradiating the surface of the patient directly without causing the accelerated electrons to collide with the target.

  In this radiotherapy apparatus 1, the subject is placed on the top 2 a, and the affected part irradiated with radiation is the axis of the rotation shaft 4 a (dotted line in the figure) and the axis of the irradiation head 5 (also dashed line in the figure). ) Is moved in the body axis direction, vertically moved and rotated, and rotated around the axis of the rotating gantry 3 so as to be located at the isocenter that intersects.

  When the affected area is located at the isocenter, the irradiation field F or the like is adjusted to irradiate the affected area with radiation from the radiation source. The irradiation field F is a region where radiation is irradiated, and is formed according to the shape of the affected part. The irradiation head 5 is provided with an original diaphragm device (multi-leaf collimator) 6, and an irradiation field F is formed by the original diaphragm device 6.

  FIG. 2 is a principle diagram viewed from the side surface showing the positional relationship between the original diaphragm device 6 and the radiation source. As shown in FIG. 2, the original aperture device 6 is installed on an exposure axis of radiation irradiated from the radiation source S. The original diaphragm device 6 includes a multi-leaf portion, and each leaf includes plate-like leaves 101A and 101B that are opposed to each other with an axis in the radiation exposure direction. The leaves 101A and 101B have a tapered cross section, and an upper end surface of the leaf 101A and 101B has an arch shape with a short circumference.

  The leaves 101A and 101B are positioned within the radiation emission range to narrow the radiation range, thereby forming an irradiation field F that matches the shape of the affected part and preventing unnecessary irradiation to tissues other than the affected part. The multi-leaf portion is composed of a pair of leaves 101A and 101B, and has a structure in which a plurality of pairs are juxtaposed so that the side surfaces thereof are in contact with each other or close to each other.

  The pair of leaves 101 </ b> A and 101 </ b> B moves independently or away along the same circular arc trajectory centered on the radiation source S. As a result of the approaching or moving away of each pair of leaves 101A and 101B, the multi-leaf portion as a whole forms a suitable field F. In FIG. 3, the schematic diagram of the power transmission system for driving each leaf in the conventional original body squeezing apparatus 6 is shown. As shown in the figure, the rotation of the motor 31 is transmitted to the leaf 37 via the worm gear 32, the worm wheel 33, the idler gear 34, the shaft 35, and the drive gear 36.

  Next, a leaf position measuring method by the radiation therapy apparatus 1 according to the present embodiment will be described. In general, optical semiconductors that detect light are more likely to cause problems such as malfunction due to photoelectric effects and Compton scattering caused by exposure to radiation, deterioration of semiconductor parts, and clouding of plastic lenses. As a result, it may be disadvantageous such that it cannot be used.

  Therefore, the radiotherapy apparatus 1 according to the present embodiment uses a “magnetic sensor” that is unlikely to cause malfunction or deterioration even when radiation is directly or indirectly applied. That is, in the radiotherapy apparatus 1 according to the present embodiment, a “magnetized magnetic tape” and a “magnetic sensor” that can detect the magnetic pattern with high sensitivity are used to measure the leaf position.

  FIG. 4 is a side view for explaining the leaf position measuring method by the radiation therapy apparatus 1 according to the present embodiment. In FIG. 4, accelerated electrons are bent in a direction by a bending magnet 42 as shown by an electron beam 41, collide with a target 43, and emit radiation 44. The arc-shaped leaf 37 of the multi-leaf collimator that controls the irradiation field of the radiation 44 has teeth on the lower surface and is connected to a motor via a power transmission mechanism 45 formed of a gear.

  In this way, the lower end face of the leaf 37 is “toothed” so as to be engaged with the drive gear, and the plurality of leaves 37 are separated from each other by a gap of several tens of μm so that radiation does not leak as much as possible. It is structured to slide. Therefore, in the radiotherapy apparatus 1 according to the present embodiment, the magnetic tape 46 magnetized at a constant pitch is attached to the upper end surface of each leaf 37, and the magnetic sensor 48 is attached to the frame 47 that guides the movement of the leaf 37. . The position of each leaf 37 can be measured with high accuracy by counting the number of voltage pulses output by the magnetic sensor 48 as the leaf 37 moves.

  As the magnetic sensor 48, a GMR sensor (= giant magnetoresistive sensor) with high sensitivity is desirable, but an interdigital AMR sensor (= different direction magnetoresistive sensor) may be used. Fig. 5-1 shows an external perspective view of the GMR sensor. Normally, the GMR sensor 51 is formed on a flat glass substrate and operates to detect a magnetic pattern generated by the magnetic tape 52. FIG. 5-2 shows an external view of the magnetic tape 52, FIG. 5-3 shows an enlarged top view of the GMR sensor 51, and FIG. 5-4 shows an enlarged bottom view of the GMR sensor 51.

  FIG. 6 shows a typical combination usage example of the GMR sensor 61 and the magnetic tape 62. In FIG. 6, a magnetized magnetic tape 62 is attached to a flat object 63, and a GMR sensor 61 slides on it to detect a pulse signal.

  On the other hand, in the radiotherapy apparatus 1 according to the present embodiment, as shown in FIG. 7, since the upper side surface of the leaf 37 is concave, a distance is generated between the magnetic sensor 48 and the magnetic tape 46. Thus, the use gap shown in the characteristic diagram of the typical magnetic sensor (GMR sensor) in FIG. 8 is exceeded. In FIG. 8, the gap indicates the distance between the surface of the magnetic sensor 48 (protective film surface) and the surface of the magnetic tape 46 (protective film surface), and the use gap indicates the allowable distance.

  Therefore, in the radiotherapy apparatus 1 according to the present embodiment, a composite material component (hereinafter referred to as “magnetic guide”) in which soft magnetic layers 81 and nonmagnetic layers 82 are alternately stacked as shown in FIG. And the magnetic tape 46.

  FIG. 10 is a view showing a magnetic guide 90 disposed between the magnetic sensor 48 and the magnetic tape 46. In order to facilitate understanding of the structure, the magnetic guide 90 is exaggerated. FIG. 10 also shows an enlarged view of a part of the contact surface between the magnetic guide 90 and the magnetic tape 46. The magnetic guide 90 pulls out the magnetic field pattern generated by the magnetic tape 46 to the magnetic sensor 48 and enables the magnetic sensor 48 to detect the magnetic field pattern. The magnetic guide 90 pulls out the magnetic field pattern generated by the magnetic tape 46 to the magnetic sensor 48, so that the magnetic sensor 48 can be arranged away from the magnetic tape 46.

  As shown in FIG. 10, the surface on which the magnetic guide 90 contacts the magnetic tape 46 is a convex surface corresponding to the upper concave side surface of the leaf 37, and the surface on which the magnetic guide 90 contacts the magnetic sensor 48 is a flat surface. The magnetic guide 90 is attached to the magnetic sensor 48.

Next, extraction of the magnetic field pattern generated by the magnetic tape 46 to the magnetic sensor 48 by the magnetic guide 90 will be described. It is known that a law similar to that of an electric circuit is established for a magnetic circuit. That is, if the magnetomotive force of the magnet is F, the total magnetic flux is Φt, and the magnetoresistance (= reluctance) of the circuit is R, the mutual relationship is expressed by the equation (1).
Φt = F / R (1)

This magnetic resistance R is expressed as in equation (2), where μ is the magnetic permeability, L is the magnetic path length of the circuit, and A is the cross-sectional area of the magnetic path. However, the magnetic permeability of vacuum is μ = 4π × 10 ⁻⁷ [H / m].
R = L / (μ · A) (2)

Whatever the positional relationship between the magnetic tape 46 and the magnetic sensor 48, the magnetization pitch of the magnetic tape 46 is set as shown in FIG. When λ and the stacking pitch of the magnetic guide 90 are λ ′, λ and λ ′ are required to satisfy the relationship of the expression (3). Here, when the thickness of the soft magnetic layer 81 is t1 and the thickness of the nonmagnetic layer 82 is t2, the stacking pitch λ ′ corresponds to the sum of t1 and t2.
λ / 2 = n · λ ′ (3)
(However, λ ′ = t1 + t2, n is a natural number of 1 or more)

Further, the material is selected so that the magnetic permeability of the nonmagnetic layer is μ and the magnetic permeability of the soft magnetic layer is μ ′, and the relationship of the formula (4) is satisfied.
μ << μ '(4)

  At this time, the magnetic field lines 83 coming out of the magnetic tape 46 are likely to pass through a layer having a large magnetic permeability, and therefore reach the magnetic guide end surface on the side not in contact with the magnetic tape 46 as shown in FIG. Will come back. Since the magnetic sensor 48 is sufficient if it has a frequency response at several kHz, the soft magnetic material constituting the soft magnetic layer 81 can have a magnetic permeability of several thousand, and the nonmagnetic layer has a relative magnetic permeability of about 1. For example, when the magnetization pitch of the magnetic tape 46 is 100 μm, it is possible to draw the magnetization pattern up to a distance of about several mm.

  FIG. 10 shows the case of n = 1 (λ / 2 = λ ′), but the case of n = 2 (λ / 2 = 2λ ′) and n = 3 (λ / 2 = 3λ ′). The cases are shown in FIGS. 12 and 13, respectively.

  An example of a method for manufacturing the magnetic guide 90 is shown in FIG. Soft magnetic particle powder having a diameter sufficiently smaller than the magnetization pitch of the magnetic tape 46 is sufficiently mixed with a radiation-resistant resin such as PEEK or polyimide, and processed into a soft magnetic sheet having a uniform thickness. The same radiation resistant resin is processed into a nonmagnetic sheet having the same thickness.

  Then, as shown in FIG. 14, the necessary number of soft magnetic sheets 91 and nonmagnetic sheets 92 are alternately stacked, and are gradually rolled by a roller 93 while being heated. When the lamination pitch reaches the desired distance λ ′, the rolling is stopped, and the magnetic guide 90 can be formed by cutting and processing into a shape that fits the magnetic sensor 48 and the leaf 37.

  As described above, in this embodiment, the flat soft magnetic layers 81 containing soft magnetic particles and the flat nonmagnetic layers 82 containing no soft magnetic particles are alternately stacked, and the exposed cross section of the stacked layers is applied to the magnetic sensor 48. The magnetic guide 90 is formed by cutting and processing into a shape suitable for the attachment surface and the contact surface with the leaf 37. Then, by arranging the magnetic guide 90 between the magnetic tape 46 and the magnetic sensor 48, a gap generated between the magnetic tape 46 and the magnetic sensor 48 due to the concave upper surface of the leaf 37. This can prevent a decrease in detection sensitivity of the magnetic field pattern. Further, direct contact between the magnetic sensor 48 and the magnetic tape 46 can be eliminated, and wear and damage of the magnetic sensor 48 itself can be prevented.

  In the above embodiment, the magnetic guide 90 is formed by alternately laminating the soft magnetic layers 81 and the nonmagnetic layers 82. However, the magnetic guide 90 is formed using a material having a columnar soft magnetic region. You can also

  FIG. 15 is a diagram showing a material composed of columnar soft magnetic regions 96 and non-magnetic regions 97. FIG. 15 also shows lines of magnetic force 83 that draw the magnetic field pattern generated by the magnetic tape to the opposite central axis cross section when the cross section of the central axis 98 of the soft magnetic region 96 is brought into contact with the magnetic tape.

In FIG. 15, the columns of the soft magnetic region are linear and are almost parallel. The cross-sectional shape of the column may be any shape, but the relationship between the pitch λ ″ between the central axes of the columns and the magnetization pitch λ of the magnetic tape is created so as to satisfy Equation (5). Here, when the outer diameter of the soft magnetic region column is t1 ′ and the distance between adjacent soft magnetic region columns (= thickness of the nonmagnetic region) is t2 ′, the stacking pitch λ ″ is t1 ′ and t2 ′. Equivalent to the sum.
λ / 2 = n ′ · λ ″ (5)
(Where λ ″ = t1 ′ + t2 ′, n ′ is a natural number of 1 or more)

  The magnetic guide 90 using the material shown in FIG. 15 can be produced as follows, for example. First, a block of radiation resistant resin is prepared, and an excimer laser or the like is used to regularly open through holes so as to have a desired shape. Then, the processed resin block is immersed in a solution in which a soft magnetic material is dissolved, and this through-hole is formed under a low temperature (24 ° C. to 100 ° C.) condition by a technique known as “ferrite plating”. Plating soft magnetic material. The magnetic guide 90 can be created by cutting and processing the resin block thus formed into a desired finished shape.

  In the present embodiment, the case where the position of each leaf 37 of the multi-leaf collimator is measured using the magnetic sensor 48 and the magnetic guide 90 in the radiotherapy apparatus 1 is described, but the present invention is not limited to this. In addition, the present invention can be similarly applied to the case where the magnetized pattern of the magnetized medium is measured using the magnetic sensor 48 and the magnetic guide 90 from a distant position.

  As described above, the present invention is useful when a magnetic sensor is used to detect a magnetized pattern of a magnetized medium from a position separated by position measurement or the like, and in particular, position measurement in an environment where radiation is used. Suitable for

It is a schematic diagram which shows the structure of the radiotherapy apparatus concerning a present Example. It is the principle figure seen from the side surface showing the positional relationship of an original body aperture device and a radiation source. It is a schematic diagram of the power transmission system for driving a leaf. It is a side view for demonstrating the leaf position measuring method by the radiotherapy apparatus concerning a present Example. It is an external appearance perspective view of a GMR sensor. It is an external view of a magnetic tape. It is an upper surface enlarged view of a GMR sensor. It is a bottom enlarged view of a GMR sensor. It is a figure which shows the typical combination usage example of a magnetic sheet and a magnetic tape. It is a figure which shows the gap which arises between a magnetic sensor and a magnetic tape. It is a characteristic view of a magnetic sensor. It is a figure which shows the composite material component by which the soft-magnetic layer and the nonmagnetic layer were laminated | stacked alternately. It is a figure which shows the magnetic guide arrange | positioned between a magnetic sensor and a magnetic tape. It is a figure which shows the magnetic force line which passes a magnetic guide. It is a figure which shows the magnetic guide of n = 2. It is a figure which shows the magnetic guide of n = 3. It is a figure which shows an example of the manufacturing method of a magnetic guide. It is a figure which shows the other material used for magnetic guide manufacture.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation therapy apparatus 2 Treatment table 2a Top plate 3 Rotation mount 3a One arm 3b One arm 4 Rotation support 4a Rotating shaft 5 Irradiation head 6 Original body aperture device 31 Motor 32 Warm gear 33 Warm wheel 34 Idler gear 35 Shaft 36 Drive gear 37, 101A , 101B Leaf 41 Electron beam 42 Bending magnet 43 Target 44 Radiation 45 Power transmission mechanism 46, 52, 62 Magnetic tape 47 Frame 48 Magnetic sensor 51, 61 GMR sensor 63 Object 81 Soft magnetic layer 82 Nonmagnetic layer 83 Magnetic field line 90 Magnetic Guide 91 Soft magnetic sheet 92 Nonmagnetic sheet 93 Roller 96 Columnar soft magnetic region 97 Nonmagnetic material region 98 Center axis of columnar soft magnetic region

Claims (7)

Flat soft magnetic layers containing soft magnetic particles and flat nonmagnetic layers containing no soft magnetic particles are alternately laminated,
A magnetic guide device that pulls out a magnetic field pattern generated by a magnetized medium to a layered exposed section opposite to the layered exposed section when the layered exposed section is brought into contact with the magnetized medium. Consists of a plurality of straight columnar magnetic regions that are soft magnetic particles, all center axes are oriented in a certain direction and are not in contact with each other and are arranged at equal intervals in two dimensions, and nonmagnetic regions that fill the gaps between the columnar magnetic regions And
When the central axis cross section of the columnar magnetic region is brought into contact with the magnetized medium, a magnetic field pattern generated by the magnetized medium is drawn out to the central axis cross section opposite to the central axis cross section. Magnetic guide device. The magnetized medium is magnetized at a constant magnetizing pitch,
3. The magnetic guide device according to claim 1, wherein a natural number multiple of a repetition pitch of the magnetic part and the non-magnetic part is equal to half of the magnetization pitch of the magnetized medium. The magnetic part is composed of a member obtained by uniformly diffusing soft magnetic particles having a maximum diameter smaller than the magnetization pitch into a radiation-resistant resin and solidifying,
The magnetic guide device according to claim 3, wherein the nonmagnetic portion is made of a radiation resistant resin.   5. The magnetic guide device according to claim 1, wherein a contact surface with the magnetized medium is convex and a surface opposite to the contact surface is a flat surface. A multi-leaf collimator that adjusts the radiation area;
A magnetized medium attached to the upper end of each arc-shaped leaf constituting the multi-leaf collimator;
A magnetic sensor for detecting a magnetic field pattern generated by the magnetized medium;
A magnetic guide device that is arranged between the magnetized medium and the magnetic sensor and extracts a magnetic field pattern generated by the magnetized medium so that the magnetic sensor can detect the magnetic pattern;
The magnetic guide device includes:
Flat soft magnetic layers containing soft magnetic particles and flat nonmagnetic layers containing no soft magnetic particles are alternately laminated,
When the laminated exposed cross section is brought into contact with the magnetized medium, a magnetic field pattern generated by the magnetized medium is drawn to the laminated exposed cross section opposite to the laminated exposed cross section so that the magnetic sensor can detect the magnetic field pattern. Radiation therapy device. A multi-leaf collimator that adjusts the radiation area;
A magnetized medium attached to the upper end of each arc-shaped leaf constituting the multi-leaf collimator;
A magnetic sensor for detecting a magnetic field pattern generated by the magnetized medium;
A magnetic guide device that is arranged between the magnetized medium and the magnetic sensor and extracts a magnetic field pattern generated by the magnetized medium so that the magnetic sensor can detect the magnetic pattern;
The magnetic guide device includes:
It is composed of a plurality of straight columnar magnetic regions that include soft magnetic particles and all center axes are oriented in a certain direction and are equally spaced two-dimensionally and a nonmagnetic region that fills a gap between the columnar magnetic regions,
When the central axis cross section of the columnar magnetic region is brought into contact with the magnetized medium, the magnetic sensor generates a magnetic field pattern generated by the magnetized medium on the cross section of the central axis opposite to the central axis cross section. It is possible to detect radiation therapy apparatus.

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