JP2008136523A - Irradiation planning method, apparatus, particle beam irradiation system and computer program for them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce burden of an irradiation object by reducing irradiation time while securing a flat and uniform dose distribution on a target. <P>SOLUTION: In a particle beam irradiation system 20, an irradiation object 6 is irradiated with a charged particle beam 2 emitted from an accelerator 22 by means of an irradiation apparatus 30. An irradiation parameter of the particle beam irradiation system is determined by an irradiation planning method. The irradiation planning method is employed to estimate irradiation error due to the particle beam irradiation system and to determine an irradiation parameter by considering the estimated irradiation error. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an irradiation planning method, an apparatus, a particle beam irradiation system, and a computer program used therefor. In particular, an irradiation planning method, apparatus, and particle beam irradiation system suitable for use in a radiotherapy apparatus and capable of reducing irradiation time and reducing the burden on the irradiation target while ensuring a flat and uniform dose distribution on the target And a computer program used for these.

  In recent years, irradiation using a charged particle beam has been widely used for breeding using the radiosensitivity of animals and plants, physical changes in substances, and cancer treatment. As one of the charged particle beam irradiation methods, there is a scanning method in which a target portion is irradiated three-dimensionally with a spot beam of a charged particle beam having a dose distribution that is locally concentrated three-dimensionally.

  In this scanning method, irradiation parameters (also referred to as treatment planning devices) are used for irradiation parameters (each of which is also referred to as a treatment planning device) so that a set target irradiation dose (also referred to as a target dose) can be uniformly irradiated to a target portion (for example, a tumor portion). It is required to determine a spot beam irradiation position, irradiation dose, etc.) by optimization calculation, and to perform irradiation as planned based on the irradiation parameters (Non-Patent Document 1).

M. Kramer et al, Treatment planning for heavy-ion radiotherapy: physical beam model and dose optimization, Phys. Med. Biol. 45, pp 3299-3317, 2000.

  However, it is difficult to irradiate as planned in the irradiation plan. In general, since the error between the planned value and the actual irradiation value is proportional to the beam intensity, it has conventionally been considered to reduce the beam intensity to a level at which this error can be ignored and to perform irradiation as planned.

  However, decreasing the beam intensity means prolonging the time required to reach the target irradiation dose, that is, the irradiation time. Considering the burden on the irradiation target due to the prolonged irradiation time, it is desirable to shorten the irradiation time as much as possible. In particular, when the scanning target is subjected to scanning irradiation a plurality of times using a specific period with little periodic fluctuation, it is necessary to further shorten the irradiation time.

  As described above, there is a trade-off between the reduction of irradiation error and the shortening of the irradiation time. With the conventional technology, a flat and uniform dose distribution is achieved as planned, and the irradiation time is shortened. There was a limit.

  The present invention has been made to solve the above-mentioned conventional problems, and while ensuring a flat and uniform dose distribution at the target, the irradiation time can be shortened and the burden on the irradiation object can be reduced. Is an issue.

  The present invention relates to an irradiation planning method for determining an irradiation parameter of a particle beam irradiation system for irradiating an irradiation target with a charged particle beam emitted from an accelerator, and estimating an irradiation error caused by the particle beam irradiation system, The above-mentioned problem is solved by determining the irradiation parameter in consideration of the estimated irradiation error.

  The present invention also provides an irradiation planning apparatus for determining irradiation parameters of a particle beam irradiation system that irradiates an irradiation target with a charged particle beam emitted from an accelerator by an irradiation apparatus, and estimates an irradiation error caused by the particle beam irradiation system. And the means for determining the irradiation parameter in consideration of the estimated irradiation error, the problem is solved.

  The present invention also provides a particle beam irradiation system including the irradiation planning device.

  The present invention is also a computer program for determining an irradiation parameter of a particle beam irradiation system that irradiates an irradiation target with a charged particle beam emitted from an accelerator by an irradiation device, and the irradiation caused by the particle beam irradiation system The object is solved by including a step of estimating an error and a step of determining an irradiation parameter in consideration of the estimated irradiation error.

  The present invention also provides a computer-readable storage medium storing the computer program.

  When the particle beam irradiation system has a function of modulating the intensity of a charged particle beam, the irradiation parameter is determined by repeatedly calculating a temporary value of the irradiation parameter, and charged particles are calculated based on the calculated temporary value of the irradiation parameter. The beam intensity can be calculated, and the estimated irradiation error can be taken into account under the condition of the calculated charged particle beam intensity.

  The intensity of the charged particle beam can be calculated according to a beam intensity table that can be irradiated by the particle beam irradiation system.

  In addition, the intensity of the charged particle beam can be calculated for each irradiation spot to be irradiated.

  In addition, the intensity of the charged particle beam can be calculated for each slice region obtained by dividing the irradiation target in the predetermined beam axis direction and intersecting the axis direction.

  Further, the irradiation error can be estimated by obtaining an error from the number of planned particles of the charged particle beam that irradiates a predetermined position of the irradiation object based on the intensity of the charged particle beam.

  Further, when each irradiation spot to be irradiated is scanned and irradiated by the irradiation apparatus, an error from the planned particle number is calculated as the intensity of the charged particle beam, the distance between the irradiation spots, and the irradiation It can be estimated from the scanning speed.

  According to the present invention, an irradiation error caused by a particle beam irradiation system such as an accelerator or an irradiation apparatus is estimated, and the irradiation parameter is determined by taking this into account, so that a flat and uniform dose distribution at the target The irradiation time can be shortened while ensuring the above. As a result, the conventional technique requires irradiation time, and the burden on the irradiation target, etc., so that scanning irradiation to a target with periodic fluctuation (for example, an organ with respiratory fluctuation) that has been considered difficult to realize is performed. And irradiation (eg, treatment) can be completed within a realistic time.

  In particular, when the particle beam irradiation system has a charged particle beam intensity modulation function and the irradiation parameter is determined under the condition of the charged particle beam intensity based on the provisional value of the irradiation parameter, the average beam intensity is reduced. The irradiation time can be further shortened.

  Further, when the beam intensity table is used when calculating the intensity of the charged particle beam, the calculation time can be shortened.

When calculating the intensity of the charged particle beam for each irradiation spot or for each slice region,
Further guarantee of a flat and uniform dose distribution at the target can be achieved.

  Further, when the irradiation error is estimated as a particle number error (hereinafter referred to as a leakage dose) from the planned particle number of a charged particle beam irradiated to a predetermined position to be irradiated, or when scanning irradiation is performed by an irradiation apparatus In the case of estimating the leakage dose, the influence of the leakage dose due to the control delay in the particle beam irradiation system can be reflected in the optimization calculation of the irradiation plan.

  Further, when the leakage dose is estimated based on the intensity of the charged particle beam, an irradiation error can be easily estimated even in scanning irradiation such as raster scanning or spot scanning.

  Further, when the leakage dose is estimated based on the intensity of the charged particle beam, the distance between the irradiation spots, and the scanning speed of irradiation, the irradiation error can be estimated easily and more accurately.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an explanatory diagram showing the overall configuration of the particle beam irradiation system according to the first embodiment of the present invention.

  As shown in FIG. 1, a particle beam irradiation system 20 includes an accelerator 22 that accelerates and emits a charged particle beam 2, a beam transport system 24 that transports the charged particle beam 2 emitted from the accelerator 22, and the beam. An irradiation device (scanning irradiation device) 30 that irradiates the target unit 6 (for example, a tumor portion) that is an irradiation target of the patient 4 with the charged particle beam 2 that has passed through the transport system 24, and a control device that controls the particle beam irradiation system 20. 40 and an irradiation planning device 42 that determines the irradiation parameters of the particle beam irradiation system 20.

  The accelerator 22 adjusts the intensity of the charged particle beam 2.

  As shown in detail in FIG. 2, the irradiation device 30 includes scanning magnets 32 and 34 for deflecting the charged particle beam 2 in the XY directions that form a plane perpendicular to the beam traveling direction (Z direction), and charged particles. A dose monitor 36 that monitors the position of the beam 2 and a range shifter 38 that adjusts the stop position of the charged particle beam 2 in the Z direction are provided so as to scan the charged particle beam 2 along the scan trajectory 8 with respect to the target unit 6. It has become.

  The control device 40 adjusts the intensity of the charged particle beam 2 from the accelerator 22, the position correction of the charged particle beam 2 in the beam transport system 24, scanning by the scanning magnets 32 and 34 of the irradiation device 30, and the range shifter 38. The beam stop position and the like are controlled.

  As shown in FIG. 1, the irradiation planning device 42 includes a computer CPU 42A for determining irradiation parameters, a program for causing the computer to function to determine irradiation parameters in consideration of irradiation errors, and necessary data. Are stored, and an interface 44 of the memory unit 42B is provided.

  The irradiation planning device 42 calculates optimum irradiation parameters such as the irradiation position and irradiation dose (weight) of each spot beam on the irradiation target, and based on the irradiation parameters, the particle beam irradiation is performed as planned. The system 20 emits a spot beam.

  As an irradiation method, as shown in FIG. 3, the spot beam is irradiated by the irradiation device 30 in accordance with the weight optimized for the planned position, so that a uniform dose is applied to the target region T as shown in FIG. A scanning irradiation method that gives distribution irradiation is often used. FIG. 3 is a distribution diagram showing the irradiation position / weight distribution of each spot beam determined by the optimization calculation of the irradiation planning device 42. FIG. 4 shows a dose distribution obtained by scanning irradiation of the irradiation apparatus 30, that is, a dose distribution by the sum of each spot beam.

  Next, with reference to FIG. 5A showing the conventional method, the irradiation procedure of the first embodiment assuming the case of irradiating a patient's tumor as an example will be described based on FIG. 5B.

  First, in step S1, the target portion 6 that is a tumor is identified by CT imaging such as X-rays.

  Based on this CT imaging, the doctor inputs the target region T of the target unit 6 to the irradiation planning device 42 in step S2. If the target area | region T is input, optimization calculation will be performed by the irradiation plan part 46 of the irradiation plan apparatus 42 by step S13 of FIG. 5 (B) by this invention.

  In step S13 of this optimization calculation, an irradiation error between the planned irradiation value and the actual irradiation value due to the performance of the particle beam irradiation system 20 such as the accelerator 22 and the irradiation device 30 is estimated. In consideration, the irradiation parameters for achieving the target dose distribution are determined. On the other hand, as shown in FIG. 5A, in step S3 in the irradiation planning unit 12 of the conventional irradiation planning apparatus 10, the irradiation error is not taken into consideration.

  When the dose distribution is calculated, the flatness in the target region T is determined in step S4. Here, the flatness can be, for example, the reciprocal of the standard deviation from the set target irradiation dose in the target region T.

  If the flatness is lower than the planned value, the process returns to step S13 to change the irradiation parameter and calculate the dose distribution again. If the flatness is higher than the planned value, the irradiation parameters at this time are input to the control device 40 as planned data in step S5. Based on the plan data, in step S6, the irradiation unit 30 irradiates the target unit 6 to kill the tumor cells and perform the treatment.

  At this time, even if there is an irradiation error due to the accelerator 22, the irradiation device 30, or the like, a uniform and flat dose distribution as planned can be obtained. On the other hand, in the conventional method, since an irradiation error is not taken into consideration, a uniform and flat dose distribution cannot be obtained.

  Next, the irradiation plan of this embodiment will be described in detail.

  In actual treatment, it is necessary to irradiate as planned based on the irradiation plan, but with the conventional technology, it was difficult to irradiate as planned. Thus, as a result of intensive studies, the present inventors have found that the performance of the accelerator 22, the irradiation device 30, and the like are one factor of irradiation errors.

  Based on this research result, the irradiation plan of this embodiment estimates the irradiation error due to the performance, and incorporates this irradiation error into the calculation of optimization of the irradiation position and irradiation dose of each spot beam in the irradiation plan. Therefore, the irradiation error is actively used.

  For example, as shown in FIG. 6, in spot scanning irradiation, irradiation is performed at a predetermined position by stopping the spot beam axis for each of a number of irradiation positions (irradiation spots) S planned in the irradiation range. The dose error R1 due to the excess of the number of particles from the planned number of charged particle beams 2 causes an irradiation error, and is caused by a delay in response of the accelerator 22, the irradiation device 30, and the like. Since the number of particles of the irradiated charged particle beam 2 can be estimated from the relationship of (beam current) × (irradiation time) / (charge amount of one particle), it is estimated by the intensity of the charged particle beam from the accelerator 22. The

  On the other hand, as shown in FIG. 7, in the raster scanning irradiation in which the movement of the beam axis does not stop at the irradiation spot S, the leakage dose R2 irradiated between the irradiation spots S also causes an irradiation error. Here, 8 in the figure represents a scan trajectory.

  This leakage dose R2, that is, the number of particles irradiated to the predetermined position of the irradiation target but not irradiated as planned within the predetermined position, that is, the particle number error due to the number of leaked particles, is caused by the accelerator 22 and the irradiation. This is caused by a delay in response of the apparatus 30 or the like, and is estimated by the intensity of the charged particle beam 2 from the accelerator 22, the distance between the irradiation spots S, and the scanning speed of irradiation of the irradiation apparatus 30.

  Then, by adding the estimated dose error R1 and leakage dose R2 to the calculation of the dose distribution, it is possible to reflect the effect of the irradiation error on the optimization calculation of the irradiation plan.

  Specifically, the flatness is obtained by calculating a dose distribution when scanning irradiation is performed under an accurate dose of each spot beam, that is, a dose corrected in consideration of the leakage dose R2. If the flatness is lower than the planned value, the irradiation parameter is changed, the leakage dose R2 is reestimated, the dose distribution is calculated, and the flatness is obtained. The above procedure is repeated until the flatness is equal to or less than the planned value, and the optimum parameter is obtained, whereby the influence of the leakage dose R2 can be reflected in the optimization calculation of the irradiation plan.

  Next, FIG. 8 shows an example of dose distribution calculation achieved by high-intensity beam irradiation according to the conventional irradiation planning method and the irradiation planning method of the present embodiment.

  As shown in FIG. 8, the dose distribution in the target area T of the AA cross section is inclined in the conventional method (A), but is flat in the irradiation planning method (B) of the present embodiment. Further, the dose distribution in the target region T of the BB cross section is curved in a mountain shape in the conventional method (A), but is flat in the irradiation planning method (B) of the present embodiment.

  When it is required to shorten the irradiation time with a high-intensity beam as in this calculation example, since the leakage dose is an amount proportional to the beam intensity, it can be actually obtained by conventional irradiation that is not based on the leakage dose. The dose distribution will not be flat. For this reason, in the conventional method, the irradiation time is prolonged because the beam intensity is weakened to enhance the therapeutic effect by the flat dose distribution.

  On the other hand, in the irradiation planning method of this embodiment, since an irradiation error is taken into account in the optimization calculation, a flat dose distribution can be obtained in the target region T even with a high-intensity beam, so that the irradiation time can be shortened. It is possible to reduce the burden on the patient.

  Further, it is also effective in the case of a treatment in which the target unit 6 that periodically changes due to breathing is scanned and irradiated a plurality of times using a specific period (respiration gate) with little respiratory change.

  Next, the irradiation procedure of 2nd Embodiment which concerns on this invention is demonstrated based on FIG.

  The present embodiment is a procedure for determining irradiation parameters when the accelerator 22 and the irradiation apparatus 30 shown in FIG. 1 have a beam intensity modulation function. Specifically, it is a procedure in the irradiation planning unit 56 shown in FIG. 9 corresponding to the irradiation planning unit 46 shown in FIG.

  First, after inputting the target region (step S2), in step S21, a first optimization calculation is performed by a repetitive calculation of a few times, and a temporary value of the irradiation parameter is calculated.

  Here, the decimal calculation is, for example, that the calculation is not repeated until the flatness of the dose distribution becomes higher than the planned value, but the calculation is terminated at a preset number of times.

  Next, in step S22, the beam intensity in the treatment is calculated for each irradiation spot from the provisional value of the irradiation parameter according to the beam intensity table 58 that can be irradiated by the accelerator 22. Here, the beam intensity table 58 of the accelerator 22 is a correspondence table between irradiation parameters and beam intensities, and can be obtained in advance through experiments or the like, for example. Further, instead of each irradiation spot, it is also possible to calculate the beam intensity for each slice region where the irradiation target is divided in the predetermined beam axis direction and intersects with the axial direction.

  When the beam intensity is calculated, in step S23, the second optimization calculation according to the present invention is performed in consideration of the performance of the accelerator 22, the irradiation device 30, and the like under the condition that irradiation is performed with the beam intensity.

  By taking such a procedure, it is possible to perform treatment with the beam intensity optimized for each irradiation spot or each slice region, and further shorten the irradiation time.

  In the determination of the flatness, for example, a criterion for reducing the leakage dose R2 between places (for example, eyes and genital organs) and irradiation spots in FIG. 7 as much as possible may be added.

  In addition to the dose error R1 and leakage dose R2, the irradiation error may be a beam position shift, a beam focus blur, or the like.

  The spot scan irradiation may be performed without moving the beam axis with a spot covering the entire irradiation field.

Explanatory drawing which shows the whole structure of the particle beam irradiation system of 1st Embodiment which concerns on this invention. Explanatory drawing which shows the structure of the irradiation apparatus of the said particle beam irradiation system Distribution diagram showing irradiation position / weight distribution of each spot beam determined by the optimization calculation of the irradiation planning device of the particle beam irradiation system Distribution diagram showing dose distribution obtained by scanning irradiation of the irradiation apparatus (A) Explanatory drawing which shows the comparison with the irradiation procedure using the irradiation plan apparatus of the conventional irradiation procedure and the (B) said embodiment. Explanatory drawing showing dose error for optimization calculation in spot scanning irradiation Explanatory drawing showing the leakage dose for optimization calculation in raster scanning irradiation (A) Distribution diagram showing comparison of dose distribution by conventional irradiation planning method and (B) irradiation planning method of the embodiment Explanatory drawing which shows the irradiation procedure of 2nd Embodiment which concerns on this invention

Explanation of symbols

2 ... charged particle beam 6 ... target part (irradiation target)
DESCRIPTION OF SYMBOLS 20 ... Particle beam irradiation system 22 ... Accelerator 30 ... Irradiation apparatus 42 ... Irradiation plan apparatus 42A ... CPU (computer)
42B ... Memory unit (program)
58 ... Beam intensity table R1 ... Dose error (irradiation error)
R2 ... Leakage dose (irradiation error)

Claims (10)

In an irradiation planning method for determining irradiation parameters of a particle beam irradiation system that irradiates an irradiation target with a charged particle beam emitted from an accelerator by an irradiation device,
Estimating the irradiation error due to the particle beam irradiation system,
An irradiation planning method, wherein an irradiation parameter is determined in consideration of the estimated irradiation error. When the particle beam irradiation system has a charged particle beam intensity modulation function,
Determining the irradiation parameters,
A temporary value of the irradiation parameter is repeatedly calculated, and the intensity of the charged particle beam is calculated based on the calculated temporary value of the irradiation parameter, and the estimated irradiation error is also calculated under the condition of the calculated charged particle beam intensity. The irradiation planning method according to claim 1, wherein the irradiation planning method is performed in consideration.   The said irradiation error is calculated | required by calculating | requiring the error from the number of plan particle | grains of the charged particle beam irradiated to the predetermined position of the said irradiation object with the intensity | strength of the said charged particle beam, The estimation of Claim 1 or 2 characterized by the above-mentioned. Irradiation planning method.   When each irradiation spot to be irradiated is scanned and irradiated by the irradiation device, an error from the number of planned particles is calculated based on the intensity of the charged particle beam, the distance between the irradiation spots, and the scanning speed of the irradiation. The irradiation planning method according to claim 3, wherein the irradiation planning method is estimated by: In the irradiation planning device for determining the irradiation parameters of the particle beam irradiation system that irradiates the irradiation target with the charged particle beam emitted from the accelerator by the irradiation device,
Means for estimating an irradiation error caused by the particle beam irradiation system;
Means for determining an irradiation parameter in consideration of the estimated irradiation error;
An irradiation planning apparatus comprising: When the particle beam irradiation system has a charged particle beam intensity modulation function,
Means for determining the irradiation parameters;
Means for repeatedly calculating the provisional value of the irradiation parameter;
Means for calculating the intensity of the charged particle beam based on the provisional value of the calculated irradiation parameter;
Means for determining an irradiation parameter in consideration of the estimated irradiation error under the condition of the calculated charged particle beam intensity;
The irradiation planning device according to claim 5, comprising:   6. The irradiation error is estimated by obtaining an error from the planned number of charged particle beams irradiated to a predetermined position of the irradiation target based on the intensity of the charged particle beam. 6. The irradiation planning device according to 6.   When each irradiation spot to be irradiated is scanned and irradiated by the irradiation device, the error from the number of planned particles is the intensity of the charged particle beam, the distance between the irradiation spots, and the scanning speed of the irradiation. The irradiation planning apparatus according to claim 7, wherein the irradiation planning apparatus is estimated by the following equation.   A particle beam irradiation system comprising the irradiation planning device according to any one of claims 5 to 8. A computer program for determining irradiation parameters of a particle beam irradiation system for irradiating an irradiation target with a charged particle beam emitted from an accelerator,
Estimating an irradiation error caused by the particle beam irradiation system;
Determining irradiation parameters in consideration of the estimated irradiation error;
A computer program comprising:

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