CN103394166B - Particle-beam therapeutic apparatus and particle-beam therapeutic method - Google Patents

Abstract

The present invention discloses a kind of particle-beam therapeutic apparatus and particle-beam therapeutic method, when the presumptive area of target volume is divided into multilamellar to irradiate particle ray along the depth direction of particle ray, performs dose modification respectively to every one deck of each layer after segmentation.

Description

Particle beam therapy device and particle beam therapy method

The present application is a divisional application entitled "particle beam therapy apparatus and particle beam therapy method" having an application date of "13/5/2008", an application number of "200880129227.9".

Technical Field

The present invention relates to a particle beam therapy system and a particle beam therapy method for treating cancer and the like by irradiating particle beams.

Background

In a known particle beam irradiation method called stack irradiation or scanning irradiation, a target volume (also simply referred to as a target) is divided in a beam traveling direction of a particle beam to perform irradiation.

In order to obtain a desired particle beam distribution in the depth direction, it is necessary to set the dose weight of each layer of the target volume to a desired value.

Therefore, although the step of dose correction is performed before irradiation, in the related art, dose correction is performed at the point of the SOBP (SpreadOutBragg Peak: enlarged Bragg Peak) center in the depth direction distribution of the biological dose.

Further, for example, patent document 1 (japanese patent laid-open No. 2004-358237) described below describes "dividing an object into a plurality of layers and determining an irradiation dose per layer", and patent document 2 (japanese patent laid-open No. 10-314323) describes "dividing an object into a plurality of layers and determining an irradiation dose per layer so as to be uniform".

Further, non-patent document 1 below shows "the influence of the position error between layers is reduced by designing the weight of the small ridge filter used for the lamination irradiation to have a gaussian distribution".

The "SOBP" and the "mini ridge filter" will be described later in the description of the embodiments of the present invention.

Patent document 1: japanese patent laid-open publication No. 2004-358237

Patent document 2: japanese patent laid-open No. Hei 10-314323

Non-patent document 1: ridgefiltrationation for the hybrid-beam-two-dimensional radial analysis for the same-ion radial analysis treatment (design and optimization of ridge filters in wide-beam three-dimensional irradiation systems for heavy ion radiotherapy) BarbaraScheffner, Tatsuaki Kanai, YasuyukiFutami, and MuneFumiShimbo, Med. Phys. volume27(4), April2000, pp716-724.

Disclosure of Invention

In the conventional laminated irradiation, dose correction is performed at the point of the representative point of the SOBP center as in the conventional enlarged irradiation.

In contrast, in the laminated irradiation, since the device setting is changed depending on the layer, it is naturally conceivable that the dose correction coefficient is provided corresponding to each layer, and there is a problem as follows: if the correction is performed at a point in the center of the SOBP, the correction coefficient of the shallow layer is not sensitive.

When the correction coefficient is found for each layer in actual measurement, a slight positional error of a portion where the dosimeter is provided causes a large error in the dose correction value because the change in the depth direction of the bragg curve is rapid, and it is difficult to perform dose correction for each layer in a short time with high accuracy.

The "bragg curve" is a curve indicating a relative dose given to the irradiation target body until the charged particles reach when the charged particle beam (for example, proton beam, carbon beam, or the like) is irradiated to the irradiation target body, and has a peak near the deepest portion.

The position error in the depth direction is mainly caused by insufficient mechanical accuracy of a dose distribution measuring apparatus used for dose correction, an error due to a shape of a dosimeter used for correction being not a two-dimensional plane, an effective thickness error of a substance such as a dose monitor in a beam line, or the like.

For these reasons, even if the correction is originally intended at the vertex of the bragg curve, the correction may be actually performed at a position other than the vertex, and it is difficult to achieve the accuracy of the correction coefficient.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a particle beam therapy system capable of performing dose correction in laminated irradiation for each layer and improving the accuracy of dose correction in laminated irradiation.

A particle beam therapy system according to the present invention is a particle beam therapy system for irradiating a particle beam by dividing a predetermined region of a target volume into a plurality of layers in a traveling direction of the particle beam, the particle beam therapy system including: a particle beam irradiation unit which has a dose monitor for monitoring the dose of the particle beam as a count value and a ridge filter for expanding a bragg peak in each of the plurality of layers, and which forms an irradiation region in the predetermined region; and a treatment control unit that controls an operation of the particle beam irradiation unit so that when a correction coefficient obtained for each of the layers by dose correction is α i, irradiation of the particle beam to the i-th layer is stopped and irradiation of a layer different from the i-th layer is shifted to when the count value reaches a value represented by the following formula (a), wherein in the dose correction, a physical dose when the particle beam is irradiated to the i-th layer of the plurality of layers is divided by the count value, a bragg peak expanded by the ridge filter has a flat region in at least a part of a physical dose PDD curve, the flat region is formed so that a width of the flat region is wider than positional accuracy achievable in the dose correction, and the correction coefficient is a correction coefficient obtained by the dose correction performed in the flat region,

k0 dMINIPEAK _ PHYS (z0) Wi/alpha i … formula (A)

Wherein,

k0: the normalization factor used to derive the prescribed dose,

dMINIPEAK _ PHYS (z 0): a value of a peak of a physical dose PDD curve of a bragg peak expanded by the ridge filter in a deepest layer in a traveling direction of the particle beam,

z 0: the depth of the PDD curve peak of the bragg peak expanded by the ridge filter,

and Wi: weighting the dose of the ith layer of the plurality of layers.

According to the present invention, it is possible to confirm the deviation of the correction coefficient of each layer while ensuring the correction accuracy of the shallow layer, and therefore, even when a failure occurs, it is possible to systematically understand the failure. Further, the positional accuracy required for dose correction can be greatly reduced, and dose correction for each of the layers in the laminated irradiation can be performed with high accuracy in a short time.

Therefore, according to the present invention, the dose correction in the laminated irradiation can be performed for each layer, and the accuracy of the dose correction in the laminated irradiation can be improved.

Drawings

Fig. 1 is a block diagram showing a particle beam therapy system.

Fig. 2 is a diagram showing a state in which a particle beam is irradiated from a particle beam irradiation unit to a patient.

Fig. 3 is a bragg curve showing the case of proton rays and carbon rays.

Fig. 4 shows a diagram of an enlarged bragg peak of a carbon ray.

Fig. 5 is a diagram for explaining the principle of the ridge filter.

Fig. 6 is a structural view showing a ridge filter mount.

FIG. 7 is a schematic diagram showing a particle beam irradiation unit and a calibration device for a dosimeter.

Fig. 8 shows a graph of a small peak (physical dose) of carbon rays.

Fig. 9 is a diagram showing the position of the correction point.

Fig. 10 is a graph showing a small peak (biological dose) of carbon rays.

Fig. 11 is a graph showing the weight of an enlarged bragg peak of a carbon ray.

Fig. 12 is a diagram showing an example of the design of a compact ridge filter according to embodiment 3.

Fig. 13 is a diagram showing an example of the design of a compact ridge filter according to embodiment 3.

Fig. 14 is a diagram showing an example of the design of a compact ridge filter according to embodiment 3.

Description of the reference symbols

1 lateral irradiation region forming part 2 dose monitor

3 Ridge filter of depth direction irradiation region forming part 4

5 data processing part 21 patient

22 treatment table 61 ridge filter mounting table

62 through aperture (through port) 70 dosimeter calibration device

71 water phantom 72 dosimeter

73 dosimeter drive device 74 dosimeter circuit and data processing device

101 treatment planning unit 102 treatment control unit

103 particle beam generating section 104 particle beam transport section

105 particle beam irradiation part 106 positioning part

Detailed Description

Embodiment mode 1

An embodiment example of the present invention is explained based on the drawings.

Fig. 1 is a block diagram showing a particle beam therapy system.

As shown in fig. 1, the particle beam therapy system includes a therapy planning unit 101, a therapy control unit 102, a particle beam generation unit 103, a particle beam transport unit 104, a particle beam irradiation unit 105, a positioning unit 106, and the like.

The particle beam irradiation unit 105 has a function of forming an appropriate irradiation field when irradiating a patient with a particle beam, and the treatment planning unit 101 has a function of determining parameters of each device of the particle beam irradiation unit 105 to appropriate values in order to irradiate a desired dose distribution. The positioning unit 106 has functions of fixing the patient, positioning and confirming the target (also referred to as a target volume), and the like.

The treatment control unit 102 controls the operations of the particle beam generation unit 103, the particle beam transport unit 104, the particle beam irradiation unit 105, and the positioning unit 106 based on instructions from the treatment planning unit 101.

Fig. 2 is a diagram showing a state in which a particle beam is irradiated from a particle beam irradiation unit to a patient.

As shown in fig. 2, the particle beam irradiation unit 105 is configured by a lateral irradiation region forming unit 1 for mainly controlling the beam in the lateral direction of the irradiation region of the particle beam (i.e., a plane perpendicular to the beam traveling direction), a dose monitor 2 for monitoring (counting) the dose of the particle beam, a depth direction irradiation region forming unit 3 for controlling the beam in the depth direction (i.e., the beam traveling direction), a ridge filter (ridge filter)4 formed in the depth direction irradiation region forming unit 3, a data processing unit 5 for processing dose data counted by the dose monitor 2, and the like. In fig. 2, 21 denotes a patient, and 22 denotes a treatment table.

Next, the control of the beam (i.e., the particle beam) in the depth direction will be described.

When a beam of a single energy is irradiated, the dose distribution in the depth direction in the patient 21 is referred to as PDD (PercentageDepthDose: percent depth dose).

When a uniform medium is irradiated with a particle beam, the particle beam stops at a certain depth according to the energy when the particle beam enters the medium, and the depth at this time is referred to as a range.

The PDD from the surface of the medium to the range has a shape called a peak of a bragg curve, and a portion near the maximum value of the curve (i.e., the bragg curve) is called a bragg peak.

Fig. 3 is a bragg curve showing the case of proton rays and carbon rays (heavy particle rays).

In fig. 3, the horizontal axis represents the depth (cm) from the body surface, and the vertical axis represents the relative absorbed dose (%).

The shape of the bragg curve differs depending on the species of the particle beam irradiated, and the bragg peak is wider in the case of proton beams than in the case of carbon beams.

Further, the carbon nucleus is subject to nuclear fission, and is not subject to nuclear fission in the proton ray, and therefore, there is no tail (i.e., tail of nuclear reaction) in the dose distribution of the proton ray.

Although the case where the particle beam is a carbon beam will be described below, the present invention is also applicable to proton beams and other species.

Fig. 4 shows a diagram of an enlarged bragg peak of a carbon ray.

In the known irradiation technique, i.e., the extended irradiation method, the width of the bragg peak is extended by an apparatus referred to as a ridge filter, and irradiation is performed while forming a region having the same dose, which is referred to as an extended bragg peak (SOBP), as shown in fig. 4.

The width of the SOBP is formed corresponding to the depth-direction thickness of the target (target volume).

Next, the difference between the biological dose and the physical dose shown in fig. 4 will be described.

The dose is defined as both a physical dose and a biological dose (also referred to as an effective dose).

The physical dose is the energy given to a certain part of the target and has units of gray (Gy).

In contrast, the biological dose is a value determined by considering biological effects on cells based on the physical dose, and the unit is gray equivalent (GyE).

The biological dose is defined by the condition of a dose equivalent to the irradiation dose by cobalt 60 such that the survival rate of cells becomes 10%, for example.

In particle beam therapy, the prescribed dose is defined by the biological dose.

The purpose of SOBP is to make the irradiation effect uniform, defined by the biological dose distribution.

In contrast, since dosimeters used in dose correction cannot measure biological effects, dose correction is performed using physical doses.

The biological dose can be determined by a known method from the physical dose, and the description thereof is omitted here.

The formation of the SOBP utilizes a device known as a ridge filter.

Fig. 5 is a diagram for explaining the principle of the ridge filter.

The ridge filter is of a known type such as a stripe ridge filter (ridge filter) or a modulation wheel (modulation wheel) as shown in fig. 5, and these are collectively referred to as the ridge filter herein.

Fig. 5 is a conceptual diagram for explaining a ridge filter, and the number of ridges is actually larger. The ridge filter 4 is constituted by regions having different thicknesses and widths.

The particle beam passes through different thicknesses depending on the position through which the particle beam passes, and thus has different ranges.

For example, if a particle beam having a water equivalent range of 30cm passes through a portion of the ridge filter having a water equivalent thickness of 5cm, the range of the particle beam is about 25cm in terms of water equivalent.

For convenience of manufacture, in practice, the thickness of the ridge filter 4 is designed to be stepped, and the proportion of the number of particles in the water equivalent thickness range is controlled in steps.

This ratio is referred to as a weight.

For example, if the thickness of the ridge filter 4 is increased by the width of the portion having a water equivalent of 5cm, the proportion of the particle beam having a range of about 25cm in terms of water equivalent can be increased.

By appropriately selecting the weights based on this known method, it is possible to design a ridge filter corresponding to an SOBP having a peak with the same biological dose.

Fig. 6 is a structural diagram showing a ridge filter mounting base, and the ridge filter 4 is mounted on a ridge filter mounting base 61 as shown in fig. 6. The structure is as follows: the ridge filter mounting base (ridge filter replacement base) 61 can be simultaneously mounted with a common ridge filter, a plurality of types of small ridge filters, and the like, and can be easily replaced.

Further, when a through hole (passage opening) 62 is provided at a certain position of the ridge mount 61 in advance, a non-modulated particle beam can be irradiated.

Conventionally, an irradiation technique called an enlargement irradiation method has been described, but a method called a laminated irradiation is known as a different irradiation technique (see the above-mentioned document 1).

In this method, a target volume is divided into regions in the depth direction, that is, layers having a certain width, and these regions are sequentially irradiated. At this time, the width of the layer does not need to be fixed.

As methods for adjusting the depth of the layer, there are two methods, that is, a method of adjusting by changing the energy of an accelerator located in the particle beam generating unit 103 and a method of adjusting by inserting a required number of plates of a certain thickness called range shifters located in the particle beam irradiating unit 105.

When the particle beam is irradiated, the bragg curve may be irradiated as it is, with a shift in a certain step unit, but when the width of the bragg peak is narrow, the step width becomes narrow, the number of steps increases, and the operation becomes complicated.

Therefore, a method of performing irradiation by intentionally enlarging the bragg peak to slightly widen the step width is employed. The step width is about 2mm to 10 mm.

In this case, the bragg peak after expansion is referred to as a mini-peak, and a device for forming the mini-peak is referred to as a mini-ridge filter.

Conventionally, it has been proposed to use a mini-ridge filter, a mini-peak having a flat weight, or a mini-peak having a weight of gaussian distribution for the layered irradiation.

However, in the conventional proposals, "flat" and "gaussian distribution" are discussed for the weight function itself, and do not refer to the PDD (PercentageDepthDose) shape of the physical dose, nor to the purpose of facilitating dose correction.

Therefore, in the conventional proposal, even if the weight of the mini-ridge filter is flat, the physical dose distribution of the mini-peak is not flat, and it is necessary to accurately determine which part of the mini-peak is to be corrected.

Further, there is a problem that a significant error occurs in the dose correction value due to a minute positional error in the depth direction.

Next, a dose correction method in the lamination irradiation will be described.

In the laminated irradiation, the irradiation needs to be performed in accordance with the output of dose calculation performed in advance in the treatment planning unit 101, in terms of the relative dose of each layer, that is, the weight of each layer. Otherwise, the desired PDD cannot be obtained.

The particle beam therapy system performs such management as: the dose to be administered to each layer is planned based on the count value of the dose monitor 2 provided in the particle beam irradiation unit 105.

That is, when a certain layer is irradiated, the dose given to the layer is converted into the count of the dose monitor 2, and when the count value reaches a desired value, the irradiation is temporarily stopped, the count is cleared, and the irradiation is shifted to the next layer.

However, since the count value of the dose monitor 2 is an arbitrary unit, the physical dose or the biological dose is not generally directly managed by the count value.

One of the reasons is that: when the device setting of the particle beam irradiation unit 105 is changed according to the irradiation conditions, it cannot be guaranteed that the count value and the physical dose always have a fixed relationship.

Instead, with a device such as that shown in FIG. 7, the count value of the dose monitor 2 is corrected for the dosimeter 72 under the desired exposure field conditions.

Fig. 7 is a configuration diagram showing the particle beam irradiation unit 105 and a calibration device for a dosimeter.

As shown in fig. 7, the dosimeter calibration device 70 is composed of a water mold (i.e., a dosimetry water tank) 71, a dosimeter 72, a dosimeter driving device 73, a dosimeter circuit and data processing device 74, and a holder 75.

For dosimeter 72, a corrective action is performed for each patient (each treatment plan) using a dosimeter that warrants correction.

The values that can be measured in the dose correction are the physical dose measured by the dosimeter 72, the count value measured by the dose monitor 2, and the ratio of these two values is the correction factor, Gy/count (gray per count value).

In the dosimeter 72, since the biological dose is not measured but only the physical dose is measured, the physical dose is corrected.

Although the prescribed dose is defined by the biological dose, dose correction and treatment radiation dose management can be performed with the PDD of the physical dose as an object by calculating the PDD of the equivalent physical dose in advance, and therefore, the biological dose does not need to be considered in dose correction.

Next, a specific example is assumed for explanation.

For example, a spherical target having a diameter of 75mm is irradiated in a layered manner.

Assuming that the step size of the layer is 2.5mm, 29 layers are required to irradiate 75mm in the depth direction.

In the conventional laminated irradiation, dose correction is performed at a point in the center of the entire SOBP formed when all 29 layers are irradiated.

This is based on the concept of the conventional enlargement irradiation method.

If expressed mathematically, the physical dose at the center of the SOBP is given by the following equation.

DSOBP_PHYS(zC)＝K0·∑dMINIPEAK_PHYS(zC+zi)·Wi

In the above equation, "DSOBP _ phys (zc)" is a function indicating the SOBP distribution, and is a physical dose expressed by gray.

"dMINIPEAK _ PHYS" is the physical dose PDD curve for the mini-peak.

zC represents the center position of the SOBP, and zi represents the shift amount of the i-th layer. Σ denotes the sum of all layers, i.e., pair i, 1, 29.

Wi is a weight of each layer normalized so as to satisfy Σ Wi ═ 1.

K0 is a normalization coefficient whose value is determined to correspond to the physical dose converted from the prescribed dose for one irradiation with DSOBP _ phys (zc).

In the above equation, the PDD curve with the small peak is shifted only by the layer to be irradiated, and the curve shape is represented by an equation obtained by superimposing the dMINIPEAK _ PHYS (zC + zi) function.

Even in the case where this assumption does not hold, the conclusion does not change as long as the function is labeled with the index i.

For example, when the radiation is prescribed with the prescribed dose at the SOBP center being 5GyE, if the physical dose DSOBP _ phys (zc) at the SOBP center is 2.05Gy, for example, the correction coefficient α 0 can be written as the following equation.

DSOBP_PHYS(zC)＝

α0·K0·∑{dMINIPEAK_PHYS(zC+zi)·Wi/α0}＝2.05Gy

At this time, "K0 · ∑{ dMINIPEAK _ PHYS (zC + zi) · Wi/α 0 }" corresponds to the count value measured by the dose monitor, and the unit of α 0 is the unit Gy/count of the correction coefficient determined in the dose correction.

Although the conventional correction method has been described so far, in the present invention, the correction of each layer is performed separately.

At this time, the physical dose at an arbitrary depth z can be described by the following formula.

DSOBP_PHYS(z)＝

K0·∑{αi·dMINIPEAK_PHYS(z+zi)·Wi/αi}

Herein, the following are defined:

Di(z)＝K0·αi·dMINIPEAK_PHYS(z+zi)·Wi/αi。

when the depth of the PDD vertex of the deepest layer is defined as z0, the depth of the peak after the shift in each layer is defined by

zpeak＝z0－zi

To give.

According to the invention, in the case of zpeak correction, the correction factor α i is determined by

αi＝Di(z0－zi)/{K0·dMINIPEAK_PHYS(z0)·Wi/αi}

Given that K0. dMINIPEAK _ PHYS (z 0). Wi/α i is equivalent to the count value measured by the dose monitor.

As described above, while only one correction coefficient Gy/count is defined in the conventional correction method, the number of correction coefficients is different from the number of layers in the correction method according to the present invention. In the existing method, since the correction coefficient is determined only at a point in the center of the SOBP, the possibility that Gy/count differs per layer is not considered.

In the prior art method, each layer contributes with a different weight to a correction value.

The weight and physical dose contributed by each layer relative to zC

K0·dSOBP_PHYS(zC+zi)·Wi

Is in direct proportion.

For layers where dSOBP _ PHYS (zC + zi) or Wi is small, the correction factor becomes dull to dSOBP _ PHYS (zC).

The following discussion is considered herein.

That is, "because the layer with smaller Wi contributes less to the dose, the correction coefficients need not be determined correctly for those layers".

However, this is contrary to the basic idea of determining the correction coefficients based on actual measurements.

If the correction coefficient need not be determined separately for shallow layers, then the following preconditions should be present: even when the irradiation conditions are changed, the value of Wi is calculated only by calculation without depending on actual measurement, and sufficient reliability can be obtained. In particular, for layers shallower than zC, correction is only taken part in by tails due to nuclear fission.

That is, in the conventional correction method, in the case of PDD having no nuclear fission tail such as proton beam, all layers shallower than zC do not participate in correction. Even in a layer with a small contribution to zC, the contribution may increase at another depth.

Therefore, it is desirable to correct each layer as in the present invention at the position of the peak of each layer, and the accuracy of dose correction can be improved and the system can be understood.

As described above, the present invention is characterized in that each layer is individually corrected, but in practice (particularly in the case of carbon rays), the bragg peak width is narrow, and therefore, it may be difficult to perform correction at the peak of the bragg peak of each layer.

Therefore, as another feature of the present invention, as shown in fig. 8, the physical dose distribution of the mini-ridge filter used in the laminated irradiation is maximized and flattened.

Fig. 8 shows a graph of a small peak (physical dose) of carbon rays.

What is important here is that flat regions of the PDD are formed in the physical dose distribution.

The width of the PDD flat section is located as the width of the mini-peak. The width of the mini-peaks needs to be greater than the positional accuracy that can be achieved in dose correction. The width of the mini-peaks and the step width of the layer may be the same, but need not be.

The correction points for the layers are schematically shown in fig. 9.

In fig. 9, the curves are drawn at intervals in order to make it easy to observe the curves of the small peaks, but in practice, the flat portions of the small peaks are adjacent to each other or overlap each other.

The small ridge filter can be designed by a known method.

For example, the shape of the physical dose PDD may be measured in advance, and the PDD curves may be added with a certain weight according to the thickness of the ridge filter, and an optimal weight may be set to form a desired flat region.

In the conventional correction method, since each layer needs to be corrected by accurately grasping the depth position of the bragg peak, it is necessary to perform correction by mapping the bragg curve in the depth direction with care at the time of correction.

The mechanical accuracy of the dose correction measurement system is sometimes insufficient with respect to the accuracy actually required.

Alternatively, even if sufficient mechanical accuracy can be obtained, time and skill are required each time to obtain high accuracy.

Thus, in the prior art, it is not practical to separately correct each layer using bragg peaks. For example, in the bragg peak of a carbon ray, even if there is a positional error of only 1mm in the depth direction, the physical dose changes by more than two times, but if a small peak having a width of 2mm is formed, the allowable error can be greatly reduced.

As described above, according to the present embodiment, even when dose correction is performed for each layer in the lamination irradiation, it is possible to perform the dose correction with high accuracy in a short time.

Since the PDD of each layer used for dose correction has a small peak with a flat physical dose, it is possible to correct the position of the dosimeter used, if any, in the small peak, and therefore, the position accuracy requirement in measurement can be greatly reduced.

Next, therapeutic irradiation using the above-described mini ridge filter will be described.

If a flat apex is formed in the physical dose distribution, the apex of the biological dose distribution is not flat, and the shape shown in fig. 10 is formed.

However, by making the width of each layer sufficiently narrow and overlapping the layers, SOBP can be formed also in a biological dose.

For example, a small peak having a width of 5mm may be overlapped with a step width of 2.5 mm.

Although the dose drops sharply on the deeper side of the mini-peak, if the mini-ridge filter is designed to be intentionally blunted, the flatness can be improved.

On the other hand, the deeper side when SOBP is formed is generally desired to have the biological dose decrease as sharply as possible.

When the weights of the respective layers for forming a uniform SOBP are examined, it is known that, as shown in fig. 11, the weights change rapidly in the vicinity of the deepest layer of the dose distribution (region in which the weights are irregular in the figure), but the weights do not change substantially in the previous region called plateau (region in which the weights are flat in the figure). (see non-patent document 1 disclosed above)

Therefore, by using both a mini ridge filter dedicated to the deepest layer for making the dose distribution of the deepest layer steep and a mini ridge filter applied to a region (a part of the plateau) having a relatively flat weight before that, it is possible to improve the flatness of the SOBP and secure the steepness of the PDD.

Although the above description is made on the premise of ensuring uniformity of the SOBP, a dose distribution in which the dose in the central portion of the SOBP is high may be desired in addition to the flat SOBP.

In the center, cancer cells having high radiation resistance may be present due to a tumor, and in such a case, it is desirable to irradiate the center with a high dose with a different dose distribution.

In this case, the correction method and the therapeutic irradiation method according to the present invention can also be applied.

Although the stacked irradiation is described above, the same method can be applied to a method called scanning irradiation in which a beamlet is irradiated.

In the scanning irradiation, the beamlets (i.e., particle beams) are overlapped in the lateral direction in addition to the lamination in the depth direction.

Even in this case, a small peak can be formed in the depth direction by using the beamlet, thereby making dose correction easy.

In this case, a modulation wheel is used as a device for forming a small peak. This is because the beamlets have difficulty impinging uniformly on the strip-ridge filter.

In the case of using a ridge filter, the pitch of the ridge needs to be made narrow.

Since the ridges of the filter can be made thin, it is easier to make the pitch of the ridges narrow.

Alternatively, it is also possible to control the beam to uniformly impinge on the ridge filter by vibrating the ridge filter.

Since the flatness can be improved by intentionally reducing the dose on the deep side of the mini-peak as in the case of the stacked irradiation, the flatness can be obtained without sacrificing the sharpness of the PDD by using both the ridge filter dedicated to the deepest layer and the ridge filter dedicated to the flat top.

As described above, the particle beam therapy system according to the present embodiment performs dose correction for each of the divided layers when the particle beam is irradiated by dividing a predetermined region of the target volume into a plurality of layers in the depth direction of the particle beam.

In addition, the particle beam therapy system according to the present embodiment is a particle beam therapy system that performs dose correction for each of divided layers when a predetermined region of a target volume is divided into a plurality of layers in a depth direction of a particle beam and the particle beam is irradiated, and performs dose correction by forming a region with a constant dose using a small ridge filter in at least a part of a width of each of the divided layers with respect to a physical dose distribution in the depth direction.

In addition, the particle beam therapy system according to the present embodiment is a particle beam therapy system that, when a predetermined region of a target volume is divided into a plurality of layers in the depth direction of a particle beam and irradiated with the particle beam, performs dose correction for each of the divided layers, and forms a region with a constant dose in at least a part of the width of each of the layers with respect to a physical dose distribution in the depth direction using a small ridge filter, and irradiates the target volume by overlapping the layers.

Embodiment mode 2

Next, embodiment 2 is described.

Although the example in which all the layers are corrected is described in embodiment 1, the setting conditions of the devices of the particle beam therapy system do not change greatly for each layer, but change only a little for each layer.

Therefore, with the accumulation of the irradiation effect, it is no longer necessary to perform the correction of each layer set forth in embodiment mode 1 at all layers at a time.

The measurement points may be considered spaced apart at intervals.

As described above, the correction points shown in fig. 9 are in a state after the interval.

For a layer spaced apart from the interval, it is conceivable to refer to the correction value of the point of correction point nearest to the layer as it is, or to interpolate the correction value using a plurality of correction execution points in the vicinity.

As the interpolation method, several known methods such as linear fitting or polynomial fitting can be considered.

When the correction system is installed, the following functions may be embedded in the control system of the correction system in advance: the user can choose whether to use all the layers as correction points or to correct them at intervals.

Further, in the case of the spaced intervals, the user may be enabled to select the positions of the spaced intervals, an interpolation algorithm, and the like.

With this embodiment, the time required for calibration can be further shortened.

As described above, the particle beam therapy system according to the present embodiment is characterized in that the dose measurement is performed only on a part of the layers selected from the divided layers.

Embodiment 3

Embodiment 3 will be described below.

Fig. 12 to 14 are diagrams for explaining examples of the design of the compact ridge filter according to the present embodiment.

In fig. 12, a flat portion of the physical dose distribution for dose correction of the portion before the bragg peak is provided.

The portion of the chain line deeper than this is designed so that the weighting of the bragg peak becomes gaussian, and thus, the coincidence with a layer deeper than the present layer can be performed more smoothly.

In fig. 13, a flat portion of the physical dose distribution for dose correction only for the central portion of the bragg peak is provided.

The flat portion is designed so that weighting of the bragg peak is gaussian distributed, and thus, coincidence with a layer deeper and shallower than the present layer can be performed more smoothly.

In fig. 14, the mini-ridge filter is designed so that a physical dose distribution (indicated by a broken line) corresponding to a dose distribution in which the biological dose is flat as shown in fig. 4 is reproduced at the deepest portion, and a flat region is present in the physical dose distribution.

In the particle beam therapy, since the dose weight in the deepest portion is high, by using such a small ridge filter optimized particularly for the dose distribution in the deepest portion, the dose distribution can be accurately reproduced even with a small number of segments of the layer in the depth direction.

As described above, in the present embodiment, the mini ridge filter having a flat physical dose can be combined with another dose distribution shape, whereby the overlapping of layers can be facilitated, or the number of layers divided can be reduced.

Industrial applicability of the invention

The present invention is suitable for realizing a particle beam therapy system capable of performing dose correction in laminated irradiation for each layer and improving the accuracy of dose correction in laminated irradiation.

Claims (2)

1. A particle beam therapy system which divides a predetermined region of a target volume into a plurality of layers in a traveling direction of a particle beam to irradiate the particle beam, comprising:

a particle beam irradiation unit which has a dose monitor for monitoring the dose of the particle beam as a count value and a ridge filter for expanding a bragg peak in each of the plurality of layers, and which forms an irradiation region in the predetermined region; and

a treatment control unit that controls an operation of the particle beam irradiation unit so that when a correction coefficient obtained for each layer by dose correction is set to α i, irradiation of the particle beam to the i-th layer is stopped and irradiation of a layer different from the i-th layer is shifted to when the count value reaches a value represented by the following formula (a), wherein in the dose correction, a physical dose at the time of irradiation of the particle beam to the i-th layer among the plurality of layers is divided by the count value,

wherein the bragg peak expanded by the ridge filter has a flat region in at least a part of a physical dose PDD curve, the flat region is formed so that a width of the flat region is larger than positional accuracy achievable at the time of the dose correction, and the correction coefficient is a correction coefficient obtained by the dose correction performed in the flat region,

k0 dMINIPEAK _ PHYS (z0) Wi/alpha i … formula (A)

Wherein,

k0: the normalization factor used to derive the prescribed dose,

dMINIPEAK _ PHYS (z 0): a value of a peak of a physical dose PDD curve of a bragg peak expanded by the ridge filter in a deepest layer in a traveling direction of the particle beam,

z 0: the depth of the PDD curve peak of the bragg peak expanded by the ridge filter,

and Wi: weighting the dose of the ith layer of the plurality of layers.

2. The particle beam therapy system according to claim 1, wherein the therapy control unit sets a target dose to be irradiated to each of the plurality of layers in accordance with an output of dose calculation performed by a therapy planning unit in advance.