JP2011120810A - Particle beam irradiation apparatus - Google Patents

Abstract

A particle beam irradiation apparatus capable of ensuring a desired dose distribution flatness over the entire region in the depth direction of an affected area without increasing the scanning range and irradiation time of the particle beam.
A particle beam irradiation apparatus includes a beam scanning unit, a scatterer that expands the beam width of a particle beam to a predetermined beam width, and an in-vivo range of the particle beam in a beam traveling direction of an affected part. A beam range expansion device that disperses and expands according to the depth, a compensation filter that matches the innermost range of the particle beam to the outer shape of the affected area, and an outer periphery of the affected area in a plane orthogonal to the beam traveling direction. A collimator that shields beam irradiation outside the shape, and a flatness monitor that measures the flatness of the dose distribution in a plane orthogonal to the beam traveling direction. Each component is a compensation filter from the side closer to the affected area. , Collimator, beam range expansion device, flatness monitor, scatterer, beam scanning unit.
[Selection] Figure 6

Description

  The present invention relates to a particle beam irradiation apparatus that irradiates an affected area with a heavy particle beam such as carbon or a proton beam, and performs cancer treatment.

  In today's Japan, cancer is the most common cause of death, with more than 300,000 people dying each year. Under such circumstances, a particle beam therapy using a carbon beam or a proton beam, which has excellent features such as a high therapeutic effect and few side effects, has attracted attention. In this therapy, cancer cells can be killed while reducing the effect on normal cells by irradiating the cancer cells with a particle beam emitted from an accelerator.

  In this treatment method, the particle beam irradiation method currently used in Japan is a method called a wobbler method (see Non-Patent Documents 1-3 and the like). This wobbler method uses a scatterer to expand the beam size (spot diameter of the beam) of the particle beam, and the expanded particle beam is an area slightly wider than the target (affected area) by an electromagnet (called a wobbler electromagnet). A flat dose distribution is formed by scanning over the entire area. The wobbler method is roughly classified into a normal wobbler method (single circle wobbler method) and a spiral wobbler method depending on the particle beam scanning method. Usually, the wobbler method is a method of scanning the particle beam along a single circle, and the spiral wobbler method is a method of scanning the particle beam in a spiral shape.

  In the wobbler method, after the dose distribution is expanded beyond the size of the affected area, the irradiation area is limited by a brass or iron collimator called a multi-leaf collimator, and irradiation is performed in accordance with the shape of the affected area. Further, a beam range expansion device called a ridge filter is provided in the beam traveling direction (beam axis direction). The width of energy in the beam axis direction is expanded to the width of the affected part in the beam axis direction by the ridge filter. Thereafter, the beam stop position is matched with the shape of the affected part (outer shape) at a deep position by a compensation filter made of polyethylene called a bolus.

Irradiation System for HIMAC, Masami TORIKOSHI et al., Journal of Radiation Research, Vol. 48 (2007), Suppl. A, May 19, 2007. Commissioning of conformal irradiation system for heavy-ion radiotherapy using a layer-stacking method, Tatsuaki Kanai et al., Medical Physics 33 (8), August 2006. Optimization of Spiral-Wobbler System for Heavy-Ion Radiotherapy, Masataka KOMORI et al., Japanese Journal of Applied Physics Vol. 43, No. 9A, 2004, pp. 6463-6467.

  In the wobbler method, it is necessary to adjust the beam size (the beam spot diameter) and the beam scanning range with respect to the affected area size in the beam cross-sectional direction in order to ensure the flatness of the dose distribution in the affected area. In the case of the wobbler method, the beam scanning range can be expressed by a wobbler radius. The wobbler radius is usually the radius of the circle in the case of the wobbler method and the maximum radius of the spiral in the case of the spiral wobbler method.

  If the beam size at the affected position is always constant, the beam scanning range can be adjusted relatively easily on the premise of the beam size. However, in reality, the beam size varies depending on the position in the depth direction of the affected area due to the influence of the ridge filter.

  The ridge filter is a device that changes the path length through which the particle beam passes and changes the attenuation characteristic for the particle beam within a predetermined width. In the ridge filter, the component of the particle beam that has passed through the short path length region has a low attenuation, so it reaches the deep part of the affected area, and the component of the particle beam beam that has passed through the long path length region has a large attenuation. Stays shallow in the affected area.

  The component of the particle beam that reaches the deep position of the affected part is not scattered so much by the ridge filter because the passage path length of the ridge filter is short, and the beam size does not change so much. On the other hand, the particle beam component at a shallow position of the affected area has a long passage path length of the ridge filter, and is greatly influenced by scattering by the ridge filter, so that the beam size is enlarged. In other words, the beam size differs between the deep position and the shallow position of the affected area due to the influence of the ridge filter. For this reason, the conditions for ensuring the flatness of the dose distribution between the deep position and the shallow position of the affected area are different, and it is necessary to ensure the flatness of the dose distribution over the entire affected area (usually within ± 2.5%). It becomes difficult.

  In order to solve this problem, the conditions are usually adjusted so that the flatness of the dose distribution can be secured at a shallow position of the affected part. Since the beam size is large at a shallow position of the affected area, a larger range is scanned with a beam in order to ensure flatness.

  Scanning a large area with respect to the size of the affected area reduces the ratio of the amount of beam irradiated to the affected area (beam utilization efficiency), and increases the irradiation time. Further, the output current value required for the power source (wobbler power source) that excites the wobbler electromagnet for scanning the particle beam increases, resulting in an increase in cost.

  The present invention has been made in view of the above circumstances, and ensures a desired dose distribution flatness over the entire region in the depth direction of the affected area without expanding the scanning range and irradiation time of the particle beam. An object of the present invention is to provide a particle beam irradiation apparatus capable of performing

  In order to solve the above problems, a particle beam irradiation apparatus according to the present invention includes a beam scanning unit that scans a particle beam in a direction orthogonal to the beam traveling direction, and sets the beam width of the particle beam to a predetermined beam width. A scatterer that expands, a beam range expanding device that disperses and expands the range of the particle beam in the body in accordance with the size of the affected part in the beam traveling direction, and the particle beam in which the range of the body is dispersed and expanded A compensation filter that matches the innermost range of the beam to the outer contour of the affected part, a collimator that shields beam irradiation to the outside of the outer peripheral shape of the affected part in a plane orthogonal to the beam traveling direction, and A flatness monitor that measures the flatness of the dose distribution in a plane orthogonal to the beam traveling direction, and each of the components from the side closer to the affected area, the compensation filter, the collimator, Serial beam Fei as expansion device, the flatness monitor, the scatterer, the beam scanning unit, is arranged in the order of, it is characterized.

  According to the particle beam irradiation apparatus according to the present invention, a desired dose distribution flatness can be ensured over the entire region in the depth direction of the affected area without expanding the scanning range and irradiation time of the particle beam. .

The figure which shows the structure of the conventional particle beam irradiation apparatus, and arrangement | positioning of each component at the time of particle beam beam irradiation. The figure which shows the structure of the conventional particle beam irradiation apparatus, and arrangement | positioning of each component at the time of position alignment of an affected part. The figure which shows an example of the beam scanning pattern of a spiral wobbler method. The figure which shows typically the relationship between the component of the particle beam which passes a ridge filter, and a passage path. The figure explaining the conventional problem that the shape of dose distribution differs greatly by the influence of a ridge filter in the deepest position and the shallowest position of an affected part. The figure which shows the structure of the particle beam irradiation apparatus which concerns on one Embodiment of this invention, and arrangement | positioning of each component at the time of particle beam irradiation. The figure which shows the structure of the particle beam irradiation apparatus which concerns on one Embodiment of this invention, and arrangement | positioning of each component at the time of position alignment of an affected part. The 1st figure explaining the effect acquired by the structure of the particle beam irradiation apparatus which concerns on one Embodiment of this invention, and arrangement | positioning of each component. The 2nd figure explaining the effect acquired by the structure of the particle beam irradiation apparatus which concerns on one Embodiment of this invention, and arrangement | positioning of each component.

  Embodiments of a particle beam irradiation apparatus according to the present invention will be described with reference to the accompanying drawings.

(1) Conventional Particle Beam Irradiation Apparatus and Beam Irradiation Method FIG. 1 is a diagram showing a configuration of a conventional particle beam irradiation apparatus 100 as a comparative example to the particle beam irradiation apparatus 1 according to the present embodiment.

  The particle beam irradiation apparatus 100 includes a positive dosimeter 2, a sub-dose meter 3, an X wobbler electromagnet 4, a Y wobbler electromagnet 5, a scatterer 6, a neutron shutter 7, a ridge filter (beam range expanding device) 8, a range shifter. (Beam range adjustment device) 9, flatness monitor 10, beam position monitor 11, X-ray tube 12, X-ray drive mechanism 13, four-leaf collimator 14, multi-leaf collimator 15, bolus (compensation filter) 16, flat A panel detector (FPD) 17 and the like are provided.

  A particle beam generated by a particle beam generator (not shown) including an accelerator such as a cyclotron passes through the positive dosimeter 2.

  The positive dosimeter 2 is for measuring the irradiation dose. The detection unit of the positive dosimeter 2 includes an ionization chamber that collects charges generated by the ionizing action of the particle beam in the casing with parallel electrodes, and a secondary electron emitted from a secondary electron emission film disposed in the casing. An SEM device that measures electrons is used. A sub-dose meter 3 having the same configuration as that of the positive dosimeter 2 is disposed on the downstream side of the positive dosimeter 2 and is used as a backup for the positive dosimeter 2. For example, if the dose values detected by the positive dosimeter 2 and the sub-dose meter 3 are different, an interlock signal is issued as an abnormality has occurred, and the irradiation of the particle beam is stopped.

  The X and Y wobbler electromagnets 4 and 5 scan the particle beam incident on the wobbler electromagnets 4 and 5 in a two-dimensional manner (X direction and Y direction) in a plane perpendicular to the beam traveling direction (beam axis direction). . The X and Y wobbler electromagnets 4 and 5 constitute a beam scanning unit. The scanning position (X, Y) of the particle beam is set by controlling the output current of a wobbler power source (not shown) connected to each of the wobbler electromagnets 4 and 5.

  The scatterer 6 is for expanding the beam to an appropriate beam size (beam spot diameter) at the target (affected part 50) position, and is made of a heavy metal film such as lead or tantalum.

  The neutron shutter 7 is embedded in a wall 63 that separates the treatment room 60 and the front room 61 (the room where the X and Y wobbler electromagnets 4, 5 and the like are disposed), and when necessary (when treatment is performed). In other cases, the beam is blocked by closing the shutter to ensure the safety of patients and medical staff in the treatment room 60.

  The ridge filter (beam range expanding device) 8 disperses and expands the in-vivo range of the particle beam according to the size of the affected part 50 in the beam axis direction. A monoenergetic particle beam has a very sharp peak dose in the body depth direction. This peak dose is called the Bragg peak. The ridge filter 8 is for dispersing and enlarging the Bragg peak so as to correspond to the size (length) of the affected part 50 in the beam axis direction. The ridge filter 8 is configured by arranging a plurality of aluminum bar pieces (bars). These rod pieces have an isosceles triangle shape, and the beam stop position, that is, the range within the body changes depending on the path length when the particle beam passes through the rod pieces. A common ridge filter 8 is used for the wobbler method and the spiral wobbler method. However, a ridge filter for a method called a layered product irradiation method, which will be described later, uses a rod-shaped ridge filter with a short height in order to expand the beam range in accordance with the slice interval.

  The range shifter (in-vivo range adjustment device) 9 adjusts the position (Z) in the beam axis direction in the affected part 50 in the body. When the in-vivo range is expanded by the ridge filter 8, the deepest position (the deepest in-vivo range) of the affected part 50 is adjusted by the range shifter 9. The range shifter 9 is composed of an acrylic plate having a plurality of thicknesses, and the beam energy passing through the range shifter 9, that is, the range of the body is adjusted by combining these acrylic plates. Although the adjustment of the in-vivo range can also be performed on the side of the particle beam generator such as a cyclotron, the fine adjustment is simpler using the range shifter 9, and therefore the range shifter is exclusively used.

  The wobbler method described above is a method of irradiating the entire affected area 50 at one time. On the other hand, the layered body irradiation method divides the affected area 50 into a plurality of slices in the beam axis direction, and sequentially irradiates the beam for each slice. It is a method to do. In the case of the layered product irradiation method, irradiation is performed while changing the insertion thickness of the acrylic plate of the range shifter step by step in accordance with the position of the slice.

  The flatness monitor 10 is a monitor for confirming whether or not the irradiation beam forms a flat dose distribution. During irradiation with the particle beam (during treatment), the particle beam is arranged on the path of the particle beam as shown in FIG.

  On the other hand, the beam position monitor 11 is a monitor for confirming that the beam position is correct under the condition that no current is supplied to the wobbler electromagnets 4 and 5 before the treatment is started.

  Further, the X-ray tube 12 generates X-rays, and whether or not the affected part 50 of the patient can be installed at the correct position by acquiring a fluoroscopic image of the patient by the FPD 17 installed facing the back side of the patient. Confirm.

  The flatness monitor 10, the beam position monitor 11, and the X-ray tube 12 are attached to the same drive mechanism (X-ray tube drive mechanism 13), and depending on each of the time of beam irradiation, beam position confirmation, and fluoroscopic image shooting. Used to change the arrangement.

  The four-spring collimator 14 and the multi-leaf collimator 15 (which may be referred to simply as a collimator together) shield the beam irradiation to the outside of the outer peripheral shape of the affected area 50 on a plane orthogonal to the beam traveling method. It is.

  The multi-leaf collimator 15 is a combination of a large number of brass or iron leaves having a thickness of about 3 mm, and can be opened and closed in accordance with the shape of the affected part by adjusting the position of each leaf with an electric or air cylinder. .

  The four-spring collimator 14 is a collimator for suppressing the leakage of the beam from the gap between the leaves of the multileaf collimator 15.

  In the case of the layered product irradiation method, the multileaf collimator 15 and the four-spring collimator 14 are irradiated while changing the position for each slice.

  The bolus (compensation filter) 16 is formed by rolling the inside of a polyethylene block in accordance with the shape of the affected part. The bolus 16 matches the beam stop position (the deepest in-vivo range) with the outer shape of the back side of the affected area 50.

  Irradiation of the particle beam is performed using each of the components described above. Below, the procedure of the spiral wobbler method among the wobbler irradiation methods will be outlined.

  First, a patient is placed on a treatment table (not shown), and the treatment table is moved so that the center of the affected part 50 of the patient is at the center of the beam axis (isocenter 51).

  Subsequently, as shown in FIG. 2, the X-ray tube 12 is disposed on the beam axis using the X-ray tube driving mechanism 13, and the FPD 17 is disposed at a position where the X-ray tube 12 faces the patient. Then, an X-ray fluoroscopic image around the affected area is acquired using the X-ray tube 12 and the FPD 17 and the X-ray fluoroscopic image is compared with a reference image acquired in advance. If the position of the affected part 50 in the X-ray fluoroscopic image matches the position of the affected part 50 in the reference image, the positioning ends. On the other hand, if there is a shift in position, the treatment table is moved by the shift amount (shift correction). Each time the treatment table is moved, an X-ray fluoroscopic image is acquired and compared with a reference image, and deviation correction is performed until the position of the affected area 50 matches.

  When the positioning of the patient is completed, the beam energy emitted from the accelerator is selected in accordance with the deepest position (the deepest body range) of the affected part. Since it is necessary to set the current values of a large number of electromagnets forming the accelerator with respect to the beam energy, it is usually selected from several set values. Fine adjustment of the deepest body range (adjustment of about 0.5 mm) is performed by adjusting the insertion thickness of the range shifter 9 which is a beam range adjustment device.

  In parallel, one ridge filter 8 is selected from several types of ridge filters in order to expand the in-vivo range in the depth direction corresponding to the maximum value of the length of the affected part 50 in the beam axis direction.

  A bolus (compensation filter) 16 manufactured based on the shape of the affected part is attached to the downstream side of the multi-leaf collimator 15 on the beam. Thereafter, the opening shape of the multileaf collimator 15 is set in accordance with the beam cross-sectional shape of the affected part 50.

  Further, the thickness of the scatterer 6 and the maximum radius of the range in which the beam is scanned by the wobbler method (this maximum radius is referred to as the wobbler radius) are set so as to sufficiently cover the beam cross-sectional shape of the affected area 50. The scanning of the beam is performed according to a predetermined output current waveform of a wobbler power supply (X, Y) (not shown), and the coefficient associated with the maximum radius for scanning the beam and the beam energy is changed to a predetermined output current waveform. By accumulating, it applies to each affected part 50 beam cross-sectional size.

In the spiral wobbler method, the trajectory drawn by the beam scanned by the wobbler electromagnet is expressed by the following (Expression 1) to (Expression 3) (Non-patent Document 3).

  Here, F is a horizontal component and a vertical component of the beam trajectory, T is an operation cycle in the radial direction, ω is each frequency of rotation, and n is an integer. A is a wobbler radius, R is an irradiation field diameter (radius), and σ is a beam size.

  FIG. 3 is a diagram showing the concept of beam scanning by the spiral wobbler method. As the helical wobbler trajectory, a modified trajectory of (Equation 1)-(Equation 3) can also be used. However, the present invention is also applicable to this case, and the same effect can be obtained. Is omitted.

  Next, the thickness of the scatterer 6 is set. The thickness of the scatterer is set so that the standard deviation σ ≧ 2.5 cm at the deepest position of the affected area. When the beam size is σ <2.5 cm, the flatness of the formed dose distribution is lowered. In other words, the difference between the dose at the peak of the particle beam and the dose at the position between the beams increases, and the dose distribution is more than acceptable. On the other hand, when the beam size is larger than 2.5 cm, the standard that the flatness is within ± 2.5% can be secured, but as the beam size increases, the range in which the flatness can be secured with respect to the same beam trajectory decreases. Become.

  When the setting for each component as described above is completed, the particle beam of the set energy is emitted from the accelerator, and the affected area 50 is irradiated.

  After the patient is positioned, the flatness monitor 10 is moved on the beam axis to monitor the flatness of the distribution formed by the beam irradiated to the affected area during irradiation. If there is an abnormality in flatness, an interlock signal is output. The accelerator stops the beam emission when it receives the interlock signal.

  The dose irradiated to the affected area 50 is measured by the positive dosimeter 2, and when reaching a preset dose, the emission of the particle beam is stopped and the irradiation is completed.

  The spiral wobbler method irradiated with such an apparatus configuration / procedure has the following problems.

  FIG. 4 illustrates the beam component that passes through the ridge filter 8. The ridge filter 8 mixes a component from a component that hardly passes through the bar 80 of the ridge filter 8 as shown by the path A to a component that passes through all the bars 80 of the ridge filter 8 as shown by the path B. The range of the body is dispersed and expanded. The component passing through the path A is the beam component that has the least loss and reaches the deepest position of the affected part 50. On the other hand, the component passing through path B is the beam component that has the greatest loss and reaches the shallowest position of the affected area 50.

  Although the particle beam is scattered while passing through the bar 80 of the ridge filter 8, the path B is most affected by scattering because the distance through the bar 80 is the longest, and this component (the beam at the shallowest position of the affected part 50). The beam size of the (component) will spread the most. On the other hand, the path A is the least affected by scattering because the distance through the bar is the shortest, and the spread of the beam size of this component (the beam component at the deepest position of the affected area 50) is the smallest.

  Therefore, as shown in FIG. 5, the dose distribution at the deepest position of the affected area and the dose distribution at the shallowest position show different distribution shapes. As can be seen from FIG. 5, the dose distribution at the deepest position is almost flat in the central part, but the dose distribution at the shallowest position has few flat areas in the central part and has a gentle slope toward both ends. Shows a decreasing trend. That is, the flatness at the shallowest position of the affected part 50 is lower than the flatness at the deepest position.

  In order to ensure a predetermined flatness from a shallow position to a deep position of the affected area 50, the dose distribution with the lower flatness, that is, the flatness of the dose distribution at the shallowest position satisfies a predetermined standard. The wobbler radius A must be determined from (Expression 1) to (Expression 3).

  For this reason, it is necessary to form an irradiation field distribution with a large wobbler radius. In order to obtain a large wobbler radius, it is necessary to increase the output current value of the wobbler power supply, which increases the power supply cost.

  Further, as can be seen from FIG. 5, since the wobbler radius, that is, the range in which the beam is scanned is larger than the affected area, the ratio of the particle beam irradiated to the affected area (beam utilization efficiency) becomes small. As a result, the irradiation time is prolonged.

  On the other hand, as described above, the layered product irradiation method divides the affected part into a plurality of regions (slices) in the depth direction, and adjusts the shape of the multileaf collimator for each slice to simulate three-dimensionally. This is a method of performing irradiation. The irradiation apparatus and its configuration by the lamination original body irradiation method are the same as those in FIG. 1, but the ridge filter is changed to that for the lamination original body irradiation method. This is because, in the layered product irradiation method, the beam is enlarged in the beam axis direction by the slice width.

  The procedure of irradiation in the layered product irradiation method is as follows. Here, it is assumed that the beam is expanded by a spiral wobbler method.

  The procedure from the positioning of the patient until the setting of each component is completed is generally the same as described above. However, the ridge filter 8 is selected for irradiating the layered original, and the range shifter 9 is set so that the beam stops at the deepest slice. The multileaf collimator 15 is set in accordance with the shape of the deepest slice.

  When the setting of each component is completed, a beam of the set energy is emitted from the accelerator, and the deepest slice of the affected part is irradiated. At this time, the dose irradiated to the deepest slice is measured by the positive dosimeter 2, and when reaching a preset dose, the emission of the beam is stopped and the slice is switched.

  In slice switching, the range shifter 9 is set so as to correspond to the position of the next slice, and the opening shape of the multileaf collimator 15 is changed in accordance with the shape of the next slice. After these are completed, the beam emission is started again, and under the monitoring of the positive dosimeter 2, irradiation of a predetermined dose is performed on the corresponding slice. Sequentially, this procedure is performed over the entire region of the affected part 50 in the length direction.

  There are the following problems similar to the problems described above even in the layered body irradiation performed by such a procedure.

  When irradiating the shallowest position of the affected area 50, the insertion thickness of the range shifter 9 is increased. On the other hand, when the deepest position of the affected part 50 is irradiated, the insertion thickness of the range shifter 9 is small. For this reason, the beam size at the shallowest position of the affected area is larger than the beam size at the deepest position of the affected area 50. Therefore, similarly to the above-described problem, the flatness at the shallowest position of the affected area 50 is lower than the flatness at the deepest position, and a predetermined flatness is ensured from a shallow position to a deep position of the affected area 50. Therefore, the wobbler radius A must be determined from (Expression 1) to (Expression 3) so that the flatness of the dose distribution at the shallowest position satisfies a predetermined standard.

  For this reason, like the above-mentioned problem, it is necessary to form an irradiation field distribution with a large wobbler radius, and the power supply cost increases as the output current value of the wobbler power supply increases. In addition, the beam utilization efficiency is small and the irradiation time is long.

(2) Particle beam irradiation apparatus and beam irradiation method according to this embodiment FIG. 6 is a diagram showing a configuration of the particle beam irradiation apparatus 1 according to the embodiment of the present invention. The types and numbers of the components shown in FIG. 6 are the same as those of the conventional particle beam irradiation apparatus 100 (FIG. 1), and the corresponding components are denoted by the same reference numerals.

  The first difference between the particle beam irradiation apparatus 1 according to the present embodiment and the conventional particle beam irradiation apparatus 100 is the arrangement order of each component.

  In the conventional particle beam irradiation apparatus 100, each component during particle beam irradiation is a bolus (compensation) from the side closer to the affected part 50 as shown in FIG. 1 (or FIG. 2 of Non-Patent Document 1). Filter 16, collimator (multileaf collimator 15, 4 spring collimator 14), flatness monitor 10, range shifter (beam range adjusting device) 9, ridge filter (beam range expanding device) 8, scatterer 6, beam scanning They are arranged in the order of parts.

  On the other hand, in the particle beam irradiation apparatus 1 according to the present embodiment, as shown in FIG. 6, a bolus (compensation filter) 16, a collimator (a multileaf collimator 15, a four-spring collimator) are arranged from the side closer to the affected part 50. 14), a ridge filter (beam range expanding device) 8, a range shifter (beam range adjusting device) 9, a flatness monitor 10, a scatterer 6, and a beam scanning unit are arranged in this order. The ridge filter 8 is disposed as close to the collimator as possible.

  The main point of the arrangement of the particle beam irradiation apparatus 1 is that the ridge filter 8 is as close to the affected area 50 as possible so that the distance between the ridge filter 8 and the affected area 50 is as small as possible.

  The bolus (compensation filter) 16 and the collimator (multi-leaf collimator 15, four-spring collimator 14) are arranged to re-approach the affected area 50 because it is necessary to accurately match the irradiation range of the particle beam with the shape of the affected area 50. However, the ridge filter 8 is disposed next to the collimator, and the ridge filter 8 is brought close to the collimator so that the distance between the ridge filter 8 and the affected part 50 is minimized.

  Further, in the conventional particle beam irradiation apparatus 100, the range shifter 9 is disposed at a position closer to the affected part 50 than the ridge filter 8, but in the particle beam irradiation apparatus 1 according to the present embodiment, this order is reversed. Thus, the ridge filter 8 is disposed closer to the affected area 50 than the range shifter 9.

  A second difference between the particle beam irradiation apparatus 1 according to the present embodiment and the conventional particle beam irradiation apparatus 100 is the positions of the X-ray tube 12 and the FPD 17 when the affected part 50 is positioned.

  In the conventional particle beam irradiation apparatus 100, as shown in FIG. 2, the X-ray tube 12 is disposed between the range shifter 9 and the collimator, and the FPD 17 is located behind the patient 50 as viewed from the irradiation source of the particle beam. Arranged on the side. In contrast, in the particle beam irradiation apparatus 1 according to the present embodiment, the positional relationship is reversed, the X-ray tube 12 is disposed on the back side of the patient, and the FPD 17 is disposed between the patient 50 and the collimator. It is said. As a result, in the particle beam irradiation apparatus 1 according to the present embodiment, the distance between the X-ray tube 12 and the FPD 17 around the patient 50 can be made closer than that of the conventional particle beam irradiation apparatus 100.

  A procedure for performing particle beam irradiation (wobbler method) using the particle beam irradiation apparatus 1 according to the present embodiment will be described below.

  First, a patient is placed on a treatment table (not shown), and the treatment table is moved so that the center of the affected part 50 of the patient is at the center of the beam axis (isocenter 51).

Subsequently, the bolus (compensation filter) 16 and the FPD 17 are moved using a drive mechanism (not shown), and the FPD 17 is arranged on the beam axis behind the multi-leaf collimator 15 (see FIG. 7). Then, an X-ray fluoroscopic image around the affected area 50 is acquired using the X-ray tube 12 and the FPD 17, and the fluoroscopic image is compared with a reference image acquired in advance. If the position of the affected part 50 in the acquired fluoroscopic image matches the position of the affected part 50 in the reference image, the positioning ends. On the other hand, if there is a deviation in the position of the affected part 50, the treatment table is moved (deviation correction) by the deviation. Each time the treatment table is moved, an X-ray fluoroscopic image is obtained, compared with the reference image, and corrected for deviation until the positions match. When positioning is completed in this way, the FPD 17 is attached to the multi-leaf collimator using the drive mechanism. The bolus (compensation filter) 16 is moved to a position on the beam axis behind the multi-leaf collimator 16 instead (see FIG. 6).

  The setting procedure for each component and the procedure from the start of irradiation of the particle beam to the end of irradiation are the same as those for the conventional particle beam irradiation apparatus 100 described above, and a description thereof will be omitted.

  In the particle beam irradiation apparatus 1 according to the present embodiment, the ridge filter 8 is as close as possible to the affected area 50 so that the distance between the ridge filter 8 and the affected area 50 is as small as possible.

  On the other hand, as described above, the particle beam is scattered while passing through the ridge filter 8, the beam component at the shallowest position of the affected area 50 has the largest beam size, and the beam size of the beam component at the deepest position of the affected area 50. The spread of is the smallest. More specifically, a beam component that passes through a region having a long passage path (a beam component that irradiates a shallow position of the affected area 50) in the bar 80 of the ridge filter 8 is subjected to large scattering to widen the beam width. Since the beam component passing through the short region (the beam component that irradiates a deep position of the affected area 50) is not significantly scattered, the spread of the beam width is also small.

  FIG. 8 schematically shows the relationship between the beam width spread by the ridge filter 8 and the beam size (beam spot diameter) at the position of the affected area 50.

  In the conventional particle beam irradiation apparatus 100, as shown in FIG. 8A, since the distance from the ridge filter 8 to the affected part 50 is large, it is greatly affected by the difference in the spread of the beam width, and the shallowest part of the affected part 50 is affected. The difference between the beam size at the position and the beam size at the deepest position is greatly different.

  On the other hand, in the particle beam irradiation apparatus 1 according to the present embodiment, as shown in FIG. 8B, the distance from the ridge filter 8 to the affected part 50 is small, so that the influence of the difference in the spread of the beam width is affected. The beam size at the shallowest position of the affected area 50 is almost the same as the beam size at the deepest position.

  As a result, in the particle beam irradiation apparatus 1 according to the present embodiment, as shown in FIG. 9, the dose distribution at the deepest position and the dose distribution at the shallowest position of the affected area show substantially the same distribution shape. become. In addition, the flatness of the dose distribution at the deepest position and the dose distribution at the shallowest position can be ensured over the entire region of the affected area 50.

  Therefore, the required wobbler radius is smaller than the wobbler radius (see FIG. 5) required in the conventional particle beam irradiation apparatus 100, and the output current value of the wobbler power source for providing the wobbler radius is also reduced. The power supply cost can be reduced.

  Further, since the difference between the affected area and the wobbler radius, that is, the range in which the beam is scanned is reduced, the ratio of the particle beam irradiated to the affected area (beam utilization efficiency) is also reduced, and the irradiation time can be shortened. .

  On the other hand, in the stacked original body irradiation method, the slice position is adjusted by adjusting the insertion thickness of the range shifter 9, but the degree of beam scattering differs depending on the insertion thickness of the range shifter 9, and the slice at a shallow position of the affected part is irradiated. Compared with the case of irradiating a slice at a deep position of the affected area, the beam width becomes larger. However, in the particle beam irradiation apparatus 1 according to the present embodiment, the position of the range shifter 9 is also located closer to the affected area 50 than the conventional particle beam irradiation apparatus 100. Therefore, the same effect as that obtained by arranging the ridge filter 8 close to the affected area 50 can be obtained by arranging the range shifter 9 close to the affected area 50.

  Both the ridge filter 8 and the range shifter 9 scatter the beam and work to increase the beam size at the affected area. However, since the range shifter 9 is made of an organic material such as acrylic, the scattering effect is not so great. On the other hand, the ridge filter 8 is made of a metal such as aluminum, and the scattering effect is larger than that of the range shifter 9. Therefore, if the ridge filter 8 is arranged at a position near the affected area 50 and the range shifter 9 is arranged upstream of the beam, the ridge filter 8 having a large scattering effect can be brought closer to the affected area 50, and the shallowest area of the affected area 50. The difference in beam size between the position and the deepest position can be further reduced.

  Furthermore, in the particle beam irradiation apparatus 1 according to the present embodiment, as shown in FIG. 7, when aligning the affected part 50, the FPD 17 is arranged near the multi-leaf collimator 15 and on the downstream side of the beam so as to sandwich the patient. Thus, the X-ray tube 12 is arranged on the opposite side of the FPD 17. By arranging the FPD 17 and the X-ray tube 12 in this way, the distance between the FPD 17 and the X-ray tube 12 can be shortened as compared with the conventional arrangement. For this reason, the X-ray dose received by the FPD 17 increases, and a clearer image can be acquired as compared with the conventional particle beam irradiation apparatus 100. As a result, it becomes easy to calculate the amount of deviation by image processing, the patient positioning time is shortened, and the load on the patient is reduced.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined.

1 Particle beam irradiation device 4 X wobbler electromagnet (beam scanning unit)
5 Y wobbler electromagnet (beam scanning unit 6 scatterer 8 ridge filter (beam range expansion device)
9 Range shifter (beam range adjustment device)
10 Flatness monitor 11 Beam position monitor 12 X-ray tube 14 Four spring collimator (collimator)
15 Multileaf collimator (collimator)
16 bolus (compensation filter)
17 FPD (Flat Panel Detector)

Claims (6)

A beam scanning unit that scans the particle beam in a direction orthogonal to the beam traveling direction;
A scatterer that expands the beam width of the particle beam to a predetermined beam width;
A beam range expansion device that disperses and expands the range of the particle beam in the body according to the size of the affected part in the beam traveling direction;
A compensation filter for matching a deepest in-vivo range of the particle beam, in which the range of the body is dispersed and expanded, with a contour shape on the back side of the affected area;
A collimator that shields beam irradiation to the outside of the outer peripheral shape of the affected area in a plane perpendicular to the beam traveling direction;
A flatness monitor for measuring the flatness of the dose distribution in a plane orthogonal to the beam traveling direction;
With
Each component is arranged in the order of the compensation filter, the collimator, the beam range expanding device, the flatness monitor, the scatterer, and the beam scanning unit from the side closer to the affected part.
A particle beam irradiation apparatus characterized by that. The beam range expanding device is disposed in proximity to the collimator,
The particle beam irradiation apparatus according to claim 1. A beam range adjusting device that adjusts the innermost range of the particle beam, further comprising:
The beam range adjusting device is disposed between the beam range expanding device and the flatness monitor.
The particle beam irradiation apparatus according to claim 1. The beam range adjusting device is disposed in proximity to the beam range expanding device,
The particle beam irradiation apparatus according to claim 3. An X-ray tube for irradiating the peripheral part of the affected part including the affected part with X-rays;
A flat panel detector for obtaining a fluoroscopic image of the peripheral part of the affected area irradiated with the X-ray,
The flat panel detector is disposed between the collimator and the affected area;
The X-ray tube is disposed at a position opposite to the flat panel detector across the affected area.
The particle beam irradiation apparatus according to claim 1. The fluoroscopic image is an image obtained for positioning the affected area before irradiation with the particle beam,
The flat panel detector is at a position on the passage path of the particle beam when the fluoroscopic image is captured, and is retracted from a position on the passage path of the particle beam when the particle beam is irradiated. Move to position,
The particle beam irradiation apparatus according to claim 5.

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