JP6094906B2 - Charged particle beam irradiation equipment - Google Patents

Description

The present invention relates to a charged particle beam irradiation equipment.

  Conventionally, a charged particle beam irradiation apparatus for treating a patient's tumor by irradiation with a charged particle beam is known. In such a charged particle beam irradiation apparatus, it is necessary to accurately set the dose distribution of the charged particle beam according to the shape of the tumor arranged at the isocenter position.

  For example, Patent Literature 1 discloses a treatment planning apparatus that determines a contour of a tumor using a cross-sectional image of a patient obtained by a CT apparatus and plans a dose distribution of a charged particle beam from the shape of the tumor. In this treatment planning apparatus, a stereoscopic image is constructed from cross-sectional images near the tumor, and the dose distribution plan is confirmed by projecting the planned dose distribution of charged particle beams onto the stereoscopic image.

JP-A-5-337208

  However, in the treatment planning apparatus described above, the dose distribution plan is confirmed on the image data, but the dose distribution of the actually irradiated charged particle beam is not measured, and the confirmation is highly reliable. I can't say that. Although it is conceivable to provide a dose distribution monitor on the path of the charged particle beam, in this case, the measurable dose distribution is at the dose distribution monitor position and is different from the dose distribution at the isocenter position. Since confirmation of the dose distribution of the charged particle beam is important for ensuring the reliability of treatment, there is a strong demand for a technique for accurately confirming the dose distribution of the charged particle beam at the isocenter position.

The present invention aims to provide a charged particle beam irradiation equipment which can accurately calculate the dose distribution of the charged particle beam at the isocenter position.

In order to solve the above-described problems, the present invention provides a charged particle beam irradiation apparatus that irradiates a patient with a charged particle beam, a treatment table on which the patient is placed, and a rotating gantry that can rotate around the treatment table. And an irradiation unit that is attached to the rotating gantry and irradiates a charged particle beam, and a dose distribution calculation unit that calculates a dose distribution of the charged particle beam, and the irradiation unit measures a dose distribution of the charged particle beam that passes therethrough. And a collimator provided downstream of the dose distribution monitor in the irradiation direction of the charged particle beam and for shaping the shape of the charged particle beam in a plane perpendicular to the irradiation direction of the charged particle beam. The irradiation direction of the charged particle beam passing through the irradiation unit is the Z-axis direction, the direction orthogonal to the Z-axis direction is the X-direction, and the direction orthogonal to both the Z-axis direction and the X-axis direction is the Y-axis direction. Extends in the X-axis direction That extends to a plurality of metal wires and the Y-axis direction and a plurality of metal wires, to detect electrons charged particle beam is generated from a metal wire which is irradiated to measure the dose distribution of the charged particle beam, a dose The distribution calculation unit fits the dose distribution data that is the measurement result of the dose distribution monitor to obtain the center position coordinates of the dose distribution data that is the measurement result, and the center position coordinates obtained by the fitting and the shape data of the collimator opening Based on the above, the measurement result of the dose distribution monitor is corrected to calculate the dose distribution of the charged particle beam downstream of the collimator in the irradiation direction of the charged particle beam.

  According to the charged particle beam irradiation apparatus according to the present invention, the dose distribution of the charged particle beam at the isocenter position can be calculated based on the measurement result of the dose distribution of the charged particle beam passing through the irradiation unit. Therefore, according to this charged particle beam irradiation apparatus, the dose distribution at the isocenter position can be confirmed before treatment by actually irradiating. Moreover, in this charged particle beam irradiation apparatus, the dose of the charged particle beam at the isocenter position is compared with the case where the actual measurement result is not used by using the measurement result of the dose distribution of the actually irradiated charged particle beam. The distribution can be calculated with high accuracy.

The charged particle beam irradiation apparatus according to the present invention, co Rimeta has a comb two rows opposed to each other in X-axis direction, the charged particles pass through the aperture by adjusting the opening between the opposing comb line The dose distribution calculation unit measures the dose distribution monitor based on the measurement result of the dose distribution monitor and the width in the X-axis direction of the opening between the comb teeth facing the multi-leaf collimator. The dose distribution of the charged particle beam on the downstream side in the irradiation direction of the charged particle beam may be calculated by correcting the result.

  According to the present invention, the dose distribution of the charged particle beam at the isocenter position can be calculated with high accuracy.

1 is a perspective view showing an embodiment of a charged particle beam irradiation apparatus according to the present invention. It is a perspective view which shows the irradiation part of the wobbler system shown in FIG. It is the schematic which shows the change of the dose distribution of the charged particle beam in an irradiation part. It is a graph which shows an example of the measurement result in a dose distribution monitor. It is a flowchart which shows the dose distribution calculation method of the charged particle beam which concerns on this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the irradiation unit 1 is attached to a rotating gantry 103 provided so as to surround the treatment table 105 in the charged particle beam irradiation apparatus 100, and is rotated around the treatment table 105 by the rotation gantry 103. It is possible. Then, a charged particle beam P (see FIG. 2) is irradiated to an irradiated object such as a tumor of a patient who is laid on the treatment table 105. The charged particle beam P is obtained by accelerating charged particles at a high speed. Examples of the charged particle beam P include proton beams and heavy particle (heavy ion) beams.

  Although not shown in FIG. 1, the charged particle beam irradiation apparatus 100 separates the cyclotron that accelerates the charged particle beam generated by the ion source and emits the charged particle beam P away from the treatment table 105 and the rotating gantry 103. Prepared in a different position. The charged particle beam P emitted from the cyclotron is supplied to the irradiation unit 1 through the beam transport system. The charged particle beam irradiation apparatus 100 is comprehensively controlled by the control apparatus 10.

  As shown in FIG. 2, the irradiation unit 1 includes a quadrupole magnet 2, a wobbling magnet 3, a scatterer 4, a ridge filter 5 and a dose distribution monitor (dose distribution measuring means) arranged in order in the irradiation direction of the charged particle beam P. 6, a multi-leaf collimator 7 and a snout 8 are provided. Hereinafter, the irradiation direction of the charged particle beam P passing through the irradiation unit 1 will be used as an explanation in the Z axis direction, and two directions orthogonal to the Z axis will be used as an X axis direction and a Y axis direction. The X-axis direction and the Y-axis direction are directions orthogonal to each other.

  The quadrupole magnet 2 closest to the entrance of the irradiating unit 1 is an electromagnet that converges while suppressing the divergence of the charged particle beam P input through the beam transport line. A wobbling magnet 3 is disposed downstream of the quadrupole magnet 2. The wobbling magnet 3 is an electromagnet for forming a uniform irradiation field by scanning a normally distributed charged particle beam P in a circular orbit.

  The scatterer 4 diffuses the charged particle beam P scanned by the wobbling magnet 3. Such a scatterer 4 is composed of, for example, a lead plate. The scatterer 4 diffuses the charged particle beam P into a wide beam having a spread in a direction orthogonal to the irradiation direction (direction in the XY plane).

  The ridge filter 5 adjusts the dose distribution of the charged particle beam P scattered by the scatterer 4. Specifically, the ridge filter 5 gives an enlarged Bragg peak (SOBP) to the charged particle beam P so as to correspond to the thickness of the tumor in the patient's body (the length of the tumor in the irradiation direction).

  The dose distribution monitor 6 measures the dose distribution of the charged particle beam P that passes therethrough. The dose distribution monitor 6 has a plurality of metal wires extending in the X-axis direction or the Y-axis direction and arranged in a lattice pattern, and detects electrons generated from the metal wires irradiated with the charged particle beam P. To do. Channel numbers corresponding to the position coordinates of the X axis and the Y axis are assigned to the plurality of metal wires, and the dose distribution of the charged particle beam P is detected by detecting electrons generated from the metal wires of the respective channel numbers. Is measured.

  The multi-leaf collimator 7 forms the shape of the charged particle beam P on a plane (XY plane) perpendicular to the irradiation direction. The multi-leaf collimator 7 has two rows of comb teeth facing each other in the X-axis direction, and the charged particle beam P passing through the opening is formed by adjusting the opening between the facing comb teeth. Instead of the multi-leaf collimator 7, a block collimator may be used. As the block collimator, a metal column or the like in which a hole is formed according to the tumor shape of the patient is used.

  The snout 8 is a member that holds a bolus for shaping the charged particle beam P in accordance with the shape of the tumor with respect to the depth in the irradiation direction (Z-axis direction). The bolus is formed so that the three-dimensional shape of the portion where the charged particle beam P reaches the maximum depth is matched with the shape of the maximum depth portion of the tumor.

  As shown in FIGS. 1 and 2, the charged particle beam irradiation apparatus 100 includes a control device 10 that performs overall control thereof. The control device 10 performs irradiation control of the charged particle beam P to the patient and position control of the multi-leaf collimator 7. Further, the control device 10 has a dose distribution calculation unit (dose distribution calculation means) 11 for calculating the dose distribution of the charged particle beam P at the isocenter position. The dose distribution calculation unit 11 calculates the dose distribution of the charged particle beam P at the isocenter position based on the measurement result of the dose distribution monitor 6.

  Next, a dose distribution calculation method in the charged particle beam irradiation apparatus 100 according to the present embodiment will be described.

  As shown in FIG. 3, the dose distribution calculation method according to the present embodiment includes a dose distribution measurement step S1 in which the dose distribution monitor 6 measures the dose distribution of the charged particle beam P, and the dose distribution calculation unit 11 in the isocenter position. A dose distribution calculating step S2 for calculating the dose distribution of the charged particle beam P at.

  Here, FIG. 4 is a schematic diagram for explaining a change in the dose distribution of the charged particle beam P in the XZ plane. In FIG. 4, the depiction of the quadrupole magnet 2, the ridge filter 5, and the snout 8 is omitted. A central axis in the irradiation unit 1 (an axis passing through the approximate center of the devices 2 to 8 constituting the irradiation unit 1) is indicated as C.

As shown in FIG. 4, the charged particle beam P incident from the beam transport line is converged by the quadrupole magnet 2, and the dose distribution is in a mountainous state like W <b> 1. The dose distribution W1 in this case can be expressed by the following equation (1) as a function f (x) of the position coordinate x. A in Formula (1) is a normalization constant. Further, μ is the center position coordinate of the actual dose distribution, and can be expressed as a distance from the center axis C (a distance in the X-axis direction). σ is the spread of the dose distribution. This function f (x) is a Gaussian (Gaussian function).

When the charged particle beam P of the dose distribution W1 is scanned by the wobbling magnet 3, the dose distribution is in the state of W2 (a state consisting of two peaks). Let R be the wobbling radius in this case. The wobbling radius R is a parameter that depends on the particle energy E of the incident charged particle beam P, the magnetic field strength B of the wobbling magnet 3, and the distance Lw from the wobbling magnet 3 to the current position of the dose distribution W2. Here, when the function g (x) representing the influence of the scanning of the wobbling magnet 3 on the linear distribution W1 is examined, it can be expressed as the following equation (2). In this case, the function D _M (x) of the dose distribution W2 can be expressed as the following formula (3). That is, the function D _M (x) can be obtained by convolving and integrating the function f (x) and the function g (x).

Thereafter, when the charged particle beam P is diffused by the scatterer 4 in the X-axis direction and the Y-axis direction, the dose distribution becomes W3. The dose distribution W3 is a dose distribution of the charged particle beam P at the position of the dose distribution monitor 6 (dose distribution measurement position). The function representing the dose distribution W3 is obtained by replacing σ included in the function f (x) with the spread σ _M at the position of the dose distribution monitor 6 in the above equation (2). This σ _M is a parameter that depends on the spread σ ₀ of the linear distribution W 1 at the time of incidence, the thickness d of the scatterer 4, and the distance L _SM from the scatterer 4 to the dose distribution monitor 6. This dose distribution W3 is measured by the dose distribution monitor 6 in the dose distribution measurement step S1.

  FIG. 5 is a graph showing an example of the measurement result of the dose distribution monitor 6. The horizontal axis represents the channel number corresponding to the X-axis coordinate of the dose distribution monitor 6, and the vertical axis represents the dose equivalent value. The dose equivalent value is a value proportional to the dose of the charged particle beam P, and the dose can be obtained by multiplying by a predetermined coefficient.

  The dose distribution calculation unit 11 performs fitting on the dose distribution data (string-line data) of the measurement results shown in FIG. For such fitting, the Levenberg-Marquardt method, the Nelder-Mead Simplex method, or the like can be used. An example of the dose distribution data after fitting is shown as a one-dot chain line in FIG.

Here, wobbling radius R _M in the spread sigma _M and the position of the dose monitor 6 of the dose distribution at the position of the dose monitor 6 can be determined in advance by calculation or actual measurement. Thus, the free parameters in the above equation (3) is only the center position coordinates mu _M of dose distribution at the position of the normalization constant A and a dose monitor 6. Since A is a normalization constant, there is no physical meaning. For this reason, the μ _M is obtained by fitting. Dose distribution calculation unit 11, a mu _M as determined by fitting, used as the center position coordinates mu _I dose distribution W4 at isocenter position.

The dose distribution W4 at the isocenter position is obtained by multiplying the above expression (3) by the effect of the multi-leaf collimator 7. The effect of the multi-leaf collimator 7 can be expressed as the following equations (4) and (5). In the following formulas (4) and (5), a is a parameter depending on the opening width q (width in the X-axis direction) of the multi-leaf collimator 7 and the like. S is a parameter that depends on the particle energy E of the incident charged particle beam P, the magnetic field strength B of the wobbling magnet 3, the distance LCI from the multi-leaf collimator 7 to the isocenter position, and the like.

The function D _I (x) representing the dose distribution W4 of the charged particle beam P at the isocenter position is obtained by convolving and integrating f (x) and g (x) with h (x). Therefore, the function D _I (x) can be expressed as the following equation (6). In the formula (6), the center position coordinates mu _I dose distribution W4 at isocenter position using mu _M obtained in fitting. Further, values determined by calculation or measurement are used for the spread σ _I of the dose distribution W4 at the isocenter position and the wobbling radius R _I at the isocenter position.

The dose distribution calculation unit 11 calculates the function D _I (x) of the dose distribution W4 of the charged particle beam P at the isocenter position based on the above formula (6) in the dose distribution calculation step S2. The dose distribution calculation unit 11 can calculate the dose distribution W4 of the charged particle beam P at the isocenter position based on the fitting data of the measurement result of the dose monitor 6 and the above equation (6). Although the calculation when the dose distribution is a function of the X-axis position coordinates has been described, the calculation can be similarly performed when the dose distribution is a function of the Y-axis position coordinates.

  According to the charged particle beam irradiation apparatus 100 and the charged particle beam dose distribution calculation method described above, the charged particle beam P at the isocenter position is based on the measurement result of the dose distribution of the charged particle beam P passing through the irradiation unit 1. The dose distribution can be calculated. Therefore, according to the charged particle beam irradiation apparatus 100 and the dose distribution calculation method, the dose distribution at the isocenter position can be confirmed before treatment by actually irradiating. Moreover, in the charged particle beam irradiation apparatus 100 and the dose distribution calculation method, since the measurement result of the dose distribution of the charged particle beam P that actually passes through the irradiation unit 1 is used, the measurement result of the dose distribution is not used. The dose distribution of the charged particle beam P at the isocenter position can be calculated with high accuracy.

  In addition, according to the charged particle beam irradiation apparatus 100 and the dose distribution calculation method, the dose distribution is calculated based on the measurement result of the actual dose distribution of the charged particle beam P using the above-described equations (1) to (6). Thus, the dose distribution of the charged particle beam P at the isocenter position can be calculated with higher accuracy.

The present invention is not limited to the embodiment described above. For example, the center position coordinates mu _I of dose distribution in isocenter position need not be the same as mu _M obtained by the fitting. When measuring the center position coordinates μp dose distribution at the position of the profile monitored by the inlet side of the profile monitor the irradiation unit 1 is to calculate the center position coordinates mu _I of dose distribution in the isocenter position with μp You can also. Specifically, it can be obtained from the following equation (7) using μp, the distance L _PM from the profile monitor to the dose distribution monitor 6, and the distance L _MI from the dose distribution monitor 6 to the isocenter position. it can.

  The present invention is not limited to the calculation of the dose distribution of charged particle beams by the wobbler method. For example, the present invention can be effectively applied to a double scatterer method in which a charged particle beam is diffused by a plurality of scatterers without using a wobbling magnet. It can also be applied to the calculation of the dose distribution of charged particle beams by the scanning method. Furthermore, the present invention is not limited to the calculation method using the function as described above, and the dose distribution at the isocenter position can be calculated by various methods.

DESCRIPTION OF SYMBOLS 1 ... Irradiation part 2 ... Quadrupole magnet 3 ... Wobbling magnet 4 ... Scattering body 5 ... Ridge filter 6 ... Dose distribution monitor 7 ... Multi-leaf collimator 8 ... Snout 10 ... Control apparatus 11 ... Dose distribution calculation part (dose distribution calculation means) 100 ... charged particle beam irradiation device 103 ... rotating gantry 105 ... treatment table C ... central axis P ... charged particle beam q ... aperture width R ... wobbling radius W1-W4 ... linear distribution

Claims (2)

A charged particle beam irradiation apparatus for irradiating a patient with a charged particle beam,
A treatment table on which the patient is placed;
A rotating gantry rotatable around the treatment table;
An irradiation unit attached to the rotating gantry and irradiating the charged particle beam;
A dose distribution calculation unit for calculating a dose distribution of the charged particle beam,
The irradiation unit is
A dose distribution monitor for measuring a dose distribution of the charged particle beam passing through;
A collimator that is provided downstream of the dose distribution monitor in the irradiation direction of the charged particle beam and performs shaping of the shape of the charged particle beam in a plane perpendicular to the irradiation direction of the charged particle beam;
The irradiation direction of the charged particle beam passing through the irradiation unit is a Z-axis direction, a direction orthogonal to the Z-axis direction is an X direction, a direction orthogonal to both the Z-axis direction and the X-axis direction is a Y-axis direction,
The dose distribution monitor has a plurality of metal wires extending in the X-axis direction and a plurality of metal wires extending in the Y-axis direction, and is generated from the metal wires irradiated with the charged particle beam. Measure the dose distribution of the charged particle beam by detecting electrons,
The dose distribution calculation unit
Fitting the dose distribution data that is the measurement result of the dose distribution monitor to obtain the center position coordinates of the dose distribution data that is the measurement result,
Based on the center position coordinates obtained by the fitting and the shape data of the opening of the collimator, the measurement result of the dose distribution monitor is corrected and the charge on the downstream side in the irradiation direction of the charged particle beam from the collimator. A charged particle beam irradiation apparatus characterized by calculating a dose distribution of a particle beam. Before SL collimator, the multi-forming is carried out of the charged particle beam, wherein the X-axis has a double row of comb teeth facing in the direction, it passes through the aperture by adjusting the opening between the comb teeth facing A leaf collimator,
The dose distribution calculation unit corrects the measurement result of the dose distribution monitor based on the measurement result of the dose distribution monitor and the width in the X-axis direction of the opening between the comb teeth facing the multi-leaf collimator. The charged particle beam irradiation apparatus according to claim 1, wherein a dose distribution of the charged particle beam is calculated downstream of the collimator in the irradiation direction of the charged particle beam.

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