JPH0691902B2 - Radiation treatment planning device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radiation treatment planning apparatus for calculating an absorbed dose of radiation in an irradiated body during radiation treatment by a medical linac or a cobalt 60 γ-ray treatment machine. is there.

[Conventional technology]

FIG. 13 is an explanatory diagram showing a state in which X-ray treatment is performed by irradiating a diseased part (irradiated body) of a human body with X-rays. In the figure,
Reference numeral 30 is an X-ray source (radiation source), 32 is a patient (human body), 34 is an affected part of the patient, and 36 is an X-ray irradiation width.

As shown in FIG. 14, most of the X-rays 38 incident on the human body 32 cause Compton scattering. That is, the X-rays 38 repel the electrons in the atoms of the human body (mostly water) 32, and at the same time, the X-rays are scattered and become scattered rays 42. The scattered rays 42 are equal to the energy given to the electrons. It is a phenomenon that energy is reduced and wavelength is lengthened. At this time, the scattering angle of the electron beam 40 is β90 ° or less.

The absorbed dose (hereinafter referred to as a dose) of the affected part 34 by the X-ray irradiation is proportional to the amount of ion pairs generated when the electron beam 40 passes through the affected part 34. Further, in the process in which the electron beam 40 enters the attention area 44 of the affected part 34, as shown in FIG. 15, the direct process in which the first Compton scattering electron directly enters the attention area 44,
Electrons emitted when the X-rays are scattered for the second time enter the region of interest 44 for one-time scattering, and electrons emitted when the X-rays are scattered three or more times enter the region of interest 44 for multiple scattering.

By the way, when the patient 32 is treated using the X-ray 38, it is necessary to know the dose of the affected part 34. This is because it is necessary to determine how much dose of X-ray 38 should be applied in order to give necessary damage to the affected part 34. Therefore, a radiation treatment planning device that executes dose calculation is required. In the conventional radiation treatment planning system, Monte Carlo method, convolution method, delta volume method, equivalent tissue air ratio (ETAR) method, power law method, scatter air ratio method, RTAR method The dose was calculated using such as.

The Monte Carlo method is a method in which calculation without three-dimensional approximation is repeated until the accuracy is sufficient by simulation, and the most accurate dose distribution can be obtained, but even if a 1 MIPS computer is used as the radiation treatment planning device, It takes more time. In order to reduce this calculation time, the convolution method calculates in advance the contribution distribution of the dose to other points due to the scattering at one point, and adds this to all the points to which the X-ray hits. The dose distribution is obtained by combining them. Further, in the delta volume method, direct rays, primary scattering rays, and other scattering rays with respect to a target point are divided and integrated in three dimensions. In contrast, ETAR
In the method, the influence of three-dimensional scattered rays is incorporated into a two-dimensional equivalent plane to perform two-dimensional integration. Power Law is the 16th
As shown in the figure, this is a correction method in the case where the nonuniformities of the densities ρ ₁ and ρ ₂ are layered in the depth direction. Here, reference numeral 46 indicates a point of interest in the attention area 44. RTAR method is a radiation source
This is a method that utilizes the fact that the absorbed dose is equal when the ratio of the irradiation field area and the perimeter as viewed from the 30 side is equal. The SAR method is a method in which the contribution of scattered radiation is converted into the equivalent irradiation field radius based on the shape of the irradiation field and the SAR table is drawn.

The radiation treatment planning apparatus using each of the above methods is generally realized by using a computer program. Further, when performing each calculation, a tomographic image by X-ray CT is widely used, and the electron density corresponding to the X-ray energy is calculated from the grayscale of the CT image and used.

Regarding the radiation treatment planning device using each of the above methods, refer to “Computer Applications in Radiation Therapy Treatment Planning”,
Radiation Medicine (“Computer Application
in Radiation Therapy Treatment Planning "; Radiatio
n Medicine) Vol. 1, No. 2, James. A. It was described in detail in James A Purdy, 1983.

[Problems to be Solved by the Invention]

Since the conventional radiation treatment planning apparatus is configured as described above, the one that calculates the contribution of scattered radiation by three-dimensional calculation is
It takes too much time to calculate and cannot be applied to actual radiation therapy.
Moreover, the one calculated by two-dimensional calculation or the like cannot sufficiently deal with the nonuniformity of the electron density and the irregularity of the irradiation field.
(International Commition on Radiation Units and M
esurements), that is, it is not possible to execute a dose calculation that can satisfy the error of the administered dose within 5% under all conditions. For example, when using the ETAR method,
There was a case where an error of 7% or more occurred.

The present invention has been made to solve the above problems, and a radiation treatment planning apparatus capable of reducing the calculation time to a practical time while minimizing the error of the calculated dose with respect to the actual dose. Aim to get.

[Means for Solving the Problems]

A radiation treatment planning apparatus according to the invention of claim (1),
The contribution distribution data part having a contribution distribution showing the distribution of the scattered radiation to the target of interest and the contribution ratio of the part of the contribution distribution from the attention point to the radiation source are Due to the correction unit that corrects with the density correction length, and the contribution rate corrected by this correction unit, multiplied by the electron density of each point corresponding to these contribution rates, and added to cause the scattered radiation at the point of interest. The calculation unit for calculating the absorbed dose is provided.

Further, in the radiation treatment planning apparatus according to the invention of claim (2), a contribution distribution data section having a contribution distribution showing a distribution of the generated electron beam with respect to the target point in the irradiated body, and another point. If a point of interest exists within the reach of the electron beam from, the point is determined to be in the target area and the contribution rate is corrected by the electron density correction length. It is provided with a calculation unit for adding the product obtained by multiplying the electron beam contribution rate at each point in the selected region by the electron density at each point to obtain the absorbed dose by the scattered electron beam at the point of interest. .

Then, the radiation treatment planning apparatus according to the invention of claim (3) includes contribution distribution data having a contribution distribution indicating a distribution of a contribution ratio of a scattered radiation or an electron beam generated by the scattering to an attention point in an irradiated object. A target area determination unit that determines a region in the irradiation target that is equal to or higher than a predetermined contribution rate in the contribution distribution and a matrix size of calculation for the region, and a region determined by the target region determination unit. A calculation unit for adding the product obtained by multiplying the contribution ratio of scattered radiation or electron beam at each point inside by the electron density of each point to obtain the absorbed dose due to the scattered radiation or electron beam at the point of interest; It is equipped with.

[Work]

The correction unit in the invention according to claim (1) corrects the contribution distribution in the direction from the point of interest to the radiation source with the electron density correction length in between, and gives the corrected contribution distribution to the calculation unit, It is possible to reduce the calculation amount in the calculation unit.

The correction unit in the invention according to claim (2) targets, as the calculation target region of the calculation unit, another point when the electron beam scattered from another point reaches the target point, and the other point. Determines the area excluded.

The target area determination unit in the invention according to claim (3) refers to, for example, a CT image to determine an area in which the contribution ratio of the scattered radiation or electron beam to the point of interest is a predetermined value or more, This area is given to the arithmetic unit as an arithmetic target area. Also, the calculation efficiency is optimized by varying the calculation matrix size according to the slope of the contribution distribution.

〔Example〕

An embodiment of the invention described in claim (1) will be described below with reference to the drawings. In FIG. 1, 10 is a radiation treatment planning device,
20 indicates X-rays (scattered rays) that are scattered at each point of the X-ray hitting area when the electron density distribution is uniform in the human body 32.
Is a contribution distribution data section in which a contribution distribution indicating the contribution rate contributing to the attention point 46 is stored, 23 is a correction section that corrects the contribution rate with the electron density correction length using the electron density distribution, and 26 is the output contribution distribution And a calculation unit that calculates the dose due to scattered radiation from the electron density at each point, and 28 is a data unit that stores the electron density at each point. The contribution distribution stored in the contribution distribution data unit 20 can be determined in advance by experiments or calculations.

Next, the operation will be described. FIG. 2 shows how an X-ray 38 is incident on an X-ray absorber such as a human body, is scattered at point A (scattering point), and is incident on an attention 46. It should be noted that
46 is called point B. At this time, the proportion (contribution rate) of the scattered radiation 42 that contributes to point B in the scattered X-rays can be expressed by the following equation.

Where μi is the average X-ray absorption coefficient in di, f (θ)
Is the probability that X-rays will be scattered at an angle of θ in Compton scattering, and C is a coefficient. Further, the equation (1) can be rewritten as follows.

Here, if μ ₁ = μ ₂ , that is, if the absorption coefficient in the human body is constant, −μ ₁ di−μ ₂ ri = −μ (di + ri) = −μ {d + ri (1-cos θi)} ...... ( 2 ′) For example, using 4 MV X-ray 38, μ = 0.03 / cm, ri = 7c
When m and θ = 25 °, exp {-μri (1-cosθ)} = 0.9
8 and if θ is smaller, −μdi−μri≈−μ
Even with d, the error in the equation (1) is 2% or less. The smaller θ is, the smaller the error is. At this time, become that way.

Next, μ ₁ ≠ μ ₂ , that is, the case where the absorption coefficient is nonuniform in the depth direction will be described with reference to FIG. The contribution rate of A ₁ is Since the absorption coefficient is almost proportional to the electron density ρ in the human body, −μ ₁ d _I −μ ₂ d _II ≈−μ (ρ ₁ d _I + ρ ₂ d _II ) ≡−μ ...
… (5) Here, is the electron density correction length obtained by correcting the depth of the human body in the direction of the radiation source up to point B with the density. In general (if the inhomogeneity spans more layers), Is. From equations (4) and (5), To get Therefore, for θ <25 °, However, Equation (7) is the contribution rate via A ₁ point.

Next, considering the contribution rate via A ₂ points, here, Therefore, Where the general formula is Is.

Equation (9) also shows that when θ ₂ <25 °, Is. Therefore, in general from equations (6) and (9), And if θi <25 °, Becomes

From the above, the correction unit 23 inputs the contribution distribution when the electron density is uniform (corresponding to the equation (12)) from the contribution distribution data unit 20, using the density in the human body 32. It suffices to perform the correction using the density correction length and output the corrected contribution distribution (corresponding to the equation (11)). In the conventional case, it means that the density correction corresponding to the equation (1) was performed.

Then, the calculation unit 26 calculates the dose of scattered rays at the point B as , Where ρ (i, j, k) is the electron density ηxb (i, j, k) of each part expressed in (i, j, k) coordinates by equally dividing the calculation area. ) Is the one expressed by the equation (11) and applied to each part. The value of ρ (i, j, k) is stored in the data unit 28 in advance. In the actual dose calculation, the inverse square correction by the distance from the radiation source and the off-axis dose ratio from the k-axis for correcting the spread of the beam as shown in FIG. 12 (A) are taken into consideration. However, since it is not directly related to the present invention, a description thereof will be omitted.

By the way, the X-ray scattering distribution (f
When the energy of X-rays is 4 MV or more, (θ)) is concentrated forward as shown in FIG. 4. Therefore, when θ is large, f (θ) is small when r is large. Therefore ex
Since the effect of the term of p {μi (1-cosθi)} is small, equation (12) may be used for such a portion. In addition, the calculation unit 26, Is calculated for each (i, j, k) matrix, exp (−μ) or exp {−μ−μi (1-
ηxb can be obtained only by multiplying by cos θi)}.

The calculation by the formula (11) is much simpler than that of the formula (1), and the calculation is the fastest and the easiest calculation for the electronic computer. Therefore, a normal computer was applied to the radiation treatment planning apparatus. In this case, the calculation time is reduced to about 1/10 of the conventional one. It should be noted that in the conventional radiation treatment planning apparatus, the calculation according to the equation (1) is executed for all areas. Further, although the calculation unit 26 executes the three-dimensional calculation, the method described above can be applied to the two-dimensional calculation.

As shown in FIG. 5, there may be nonuniformity of the electron densities ρ ₁ and ρ ₂ in the i direction, but in order to correct the nonuniformity,
The equation (12) may be corrected as follows. In other words, you may multiply exp {-μ (i ₁ −i ₂ )} (14). However, in this case, an error occurs when the X-ray is obliquely incident, but the error is small at the point where the contribution rate is large (point closer to point B).

When θ is small, , Exp {-μ [(i-i) + (i-i)]} ≈1-μ {(i-i) + (i-i)} ...
(16) Alternatively, exp {−μ (−d + i ₁ −i ₂ )} ≈1−μ (−d + i ₁ −i ₂ ) ... (17) can be approximated. In this way, the calculation time can be further shortened. The error in such an approximation is less than 1% under actual conditions, which is sufficiently practical. Further, i in the equation (16) is However, it takes a little time to calculate. Where d
(I, j, k) is the size of the square voxel. Therefore, May be Here, ri may be calculated in advance corresponding to each matrix.

FIG. 6 is a block diagram showing a radiation treatment planning apparatus according to an embodiment of the invention set forth in claim (2). In FIG. 6, 12 is a radiation treatment planning device, and 21 is a contribution that an electron beam (direct line) generated from each point of a portion of the human body 32 where X-rays hit when the electron density is uniform contributes to point B. Contribution distribution data section 24, in which the contribution distribution indicating the rate is stored, defines the boundary between the point where the electron beam from that point reaches point B and the point where it does not, and determines the calculation target area. A correction unit that corrects the contribution rate with the electron density correction length,
Reference numeral 26 is a calculation unit that calculates the dose due to the direct line from the contribution distribution and the electron density at each point for the target area, and 28 is a data unit that stores the electron density at each point.

Next, the operation will be described. FIG. 7 shows an example in which the human body 32 is divided into 5 mm square areas. The contour lines in the figure indicate lines having the same contribution rate ηe of the electron beam to the point B. The incident X-ray 38 scatters at point A having a contribution rate ηe = 0.01, and the electron beam incident at point B is given by ρaηe = 0.01ρa, where ρa is the electron density at point A. Therefore, the dose Deb due to all electron beams (all direct rays) to the attention area (B area) including point B is Given in. Where ρ (i, j, k) is the electron density of the cube indicated by (i, j, k) coordinates, and ηeb (i, j, k) is the (i, j, k) cube for the B region. Is the contribution rate of the electron beam.

By the way, the addition of ηe (i, j, k) in equation (19)> 0.0
You only have to do this for area 01. This is because, as shown in FIG. 8, the electron beam has a predetermined range (reachable range), and the contribution from outside the point of ηe <0.01 is not immediately outside.

Here, the contribution distribution of the electron beam in the human body 32 is the electron density ρ
It depends on In particular, the actual contribution distribution in the human body 32 is substantially determined by the B area and the density of cubes in the direction of the radiation source from the B area. Therefore, if the correlation between the distribution of ηe and the distribution of η (i, j, k) as shown in FIG. 8 is obtained, η (i,
The distribution of ηe can be obtained from the distribution of j, k). In particular, ηe is generally predictable only by looking at the change in ρ (i, j, k) in the j direction.

Therefore, the distribution of ρ (i, j, k), that is, the distribution of the electron density is stored in the data unit 28, and the contribution rate of the electron beam corresponding to the electron density is stored. Then, the correction unit 24
From the distribution of the electron density in the j direction and the contribution rate of the electron beam corresponding to the electron density, the contribution distribution of the electron beam considering the electron density in the human body 32 can be determined. At that time, the calculation unit
In 26, the range of ρ (i, j, k) to be targeted is determined in consideration of the calculation accuracy and the calculation time required. The range may be within the range of the electron beam. In this way, by determining the calculation target range in the calculation unit 26,
The calculation time of the calculation unit 26 can be further shortened.

By the way, the contribution rate of the electron beam is as follows when the X-ray is scattered at the point A as shown in FIG. Can be expressed as Where is the electron density correction length along di, Is the electron beam range R when the X-ray energy is E
(E) and the electron density correction length along ri that has already been described The range function, fe (θ), determined by and, is the probability that an electron beam scatters at an angle of θ. Therefore, for the (i, j, k) cube in (20) Is calculated and allocated, again calculated for each (i, j, k) cube, tabulated, each data is drawn from the table, and ηe is determined only by calculating It can also be configured to.

As a method of determining the target area, it is possible to add ρi from the point B in the direction of the radiation source 30 to the point of reaching the range R (E) as the target area. It is advisable to prepare several types of ηe according to the energy E of X-rays and the value of electron density. The distribution of ηe is determined by g (, R (E) in the part where θi is small in Fig. 3, and by fe (θi) in the part where θi is large. Yes, the above determination method is a good approximation.

In addition, as shown in FIG. 10, the electron density is added up to a portion which becomes the range R (E) in a predetermined order, and is obtained. At this time, with respect to the point B of each (i, j, k) cube Weighting Wb (i, j, k) is decided, Can be obtained, and ηe with respect to this ρ _T can be drawn, or ηe can be drawn directly.

Then, when obtaining ηe of the equation (20), May be Here, the cubes corresponding to ρa and ρb are made larger. In this way, can be calculated in a shorter time. Note that this method can be used not only for X-ray irradiation but also for calculating the total amount of electron beam irradiation.

FIG. 11 is a block diagram showing a radiation treatment planning system according to an embodiment of the invention as set forth in claim (3). In FIG. 11, 14 is a radiation treatment planning device, 22 is a contribution rate at which scattered rays at each point of the human body 32 exposed to X-rays contribute to point B, or a direct line from each point is at point B. Contribution distribution data section that stores the contribution distribution that indicates the contribution rate that contributes, 25
Defines the boundary between points where the contribution rate to point B is greater than or equal to a predetermined value based on CT images, etc.,
The target area determination unit that determines the area within the boundary as the target area and the spatial matrix size of the calculation, 26 is the total amount caused by scattered rays or direct rays from the contribution distribution and electron density at each point for the target area This is a calculation unit that calculates the dose. Further, 28 is a data section in which the electron density etc. of each point is stored.

Next, the operation will be described. FIG. 12 is a three-dimensional contour line showing the contribution distribution of the scattered ray 42 or the electron beam 40 to the point B. In the figure, points P and Q indicate that they are the same point. As is clear from the figure,
On the i-j plane, points having the same distance from point B have the same contribution rate to point B. In the k direction, only points above the point B have a high contribution rate. However, this figure shows the case where the electron density is uniform, and when the electron density distribution is not constant, the contribution distribution is slightly different from that shown in FIG. Also, the numerical values are for explanation, and are not quantitatively accurate.

In this case, the target area determination unit 25 determines an area having a high contribution rate based on the shading of the CT image (indicated by slices 51 to 55 in FIG. 12). For example, a region in which the contribution rate ηb is 0.001 or more is determined. In Figure 12, slices 52,54
The area between the double lines is the target area. Arithmetic unit 26
Is input the contribution data from the contribution distribution data section 22 and the electron density from the data section 28, and for the area determined by the target area determination section 25, multiplies the corresponding values and adds the results. Output dose Db. In general, the target area is divided into small areas, that is, (i, j, k) areas for calculation ((i, j, k) indicates coordinates, and i, j, k are natural numbers). Therefore, the calculation is performed as follows.

Where ρ (i, j, k) is the electron density in the (i, j, k) region and ηb (i, j, k) is the contribution rate of the (i, j, k) region (η
b (i, j, k) = ηxb (i, j, k) + ηeb (i, j, k)). The calculation target is the region of ηb (i, j, k) ≧ 0.001.
Conventionally, the calculation is performed for all the regions within the frame of (B), (C), and (D) of FIG. The slices 52,54
The density of the region between can also be obtained by interpolation. As described above, by limiting the target area, the calculation time can be shortened even when the three-dimensional calculation is performed.

The contributions of the other slices 52 and 54 may be renormalized to the slice 53 having the point B (indicated by a broken line in FIG. 12 (B)). First, the dose Db _N for the slice N (N is the slice number) is obtained as follows.

Here, (i, j, k) is a region on the slice N. At this time, Db is obtained as follows.

Here, W _N is a factor that converts each (i, j, k) area into the ratio of the actual irradiation field volume and matches the absolute value of Db, and each (i, j, k) area is equally divided. If Becomes By doing so, the three-dimensional calculation can be executed in several times as long as the two-dimensional calculation. On the other hand, if i, j, and k each take a value of 1 to 40, in the conventional case,
It took 40 times longer than 2D calculation. In addition, conventional
In the radiation treatment planning apparatus using the ETAR method, accurate renormalization based on such a contribution distribution is not taken into consideration in the renormalization of the three-dimensional contribution into the two-dimensional, and the error may be large.

Further, the size of the (i, j, k) region may be selectively used in accordance with the gradient of the contribution distribution, and the size of the (i, j, k) region may be increased at a small gradient. By doing so, it is possible to further reduce the calculation time while preventing deterioration of accuracy. For example, in the equation (23), in the slices 52 and 54 other than the slice 53 including the point B, the gradient of the contribution distribution to the point B is small. Therefore, the calculation is performed as follows using a wide size.

(However, W ₅₃ <W ₅₂ = W ₅₄ ) Here, the ratio of W ₅₃ and W ₅₂ is set so as to correct the volume ratio. That is, the target area determination unit 25 increases the size of the portion where the contribution distribution has a small gradient.
In addition, the size may be changed according to the gradient of the contribution distribution even within the same slice. Further, it may be applied to the size when the electron density between slices is obtained by interpolation.

Further, the TPR value and SPR value corresponding to the dose in the target area may be used. Here, depth is d, irradiation field area S, equivalent radius And the equivalent depth dn Ask more. Further, the correction radius rn is calculated from rn = ρnr.
ρn is Is. That is, Dc = d · TPR (dn, rn), (d is a constant)
Becomes Dc is the dose at the isocenter.

By doing so, it is possible to suppress variations in the TPR value of the radiation irradiation apparatus due to differences in manufacturers without correcting ηb (i, j, k). Further, by comparing ρn, dn with ρ, d, it is possible to check the error of the operation. Here, a TAR value, a PDD value, or the like may be used instead of the TPR value. The TPR value is the tissue phantom ratio, the TAR value is the tissue air dose ratio, and the PDD value is the depth percentage.

In addition, only the dose due to the region with a high
Calculated by equation (23), the dose due to the region with a low contribution ratio is SP
It may be obtained from the R value. That is, In equation (27), the first term on the right side is a direct line,
The second term is a term relating to scattered radiation, and a is a coefficient including a field factor. The SPR is the scattering peak dose ratio.

Since most of the arithmetic operations by the arithmetic unit 26 are arithmetic operations by addition, when an electronic computer is applied as the radiation treatment planning apparatus, fixed-point arithmetic operations can be performed so that the arithmetic operations can be performed at high speed. Since the conventional ETAR method requires a lot of exponential calculation and division, floating point arithmetic is required, which takes a considerable amount of time.

〔The invention's effect〕

As described above, according to the invention described in claim (1), the radiation treatment planning apparatus corrects the contribution rate of scattered rays when the electron density given in advance is uniform by using the electron density correction length. Since the dose is calculated using the contribution rate and the electron density distribution, there is an effect that the dose can be output in a short time while maintaining high accuracy.

According to the invention of claim (2), the radiation treatment planning apparatus corrects the contribution rate of the electron beam when the electron density given in advance by the electron density correction length is uniform, and the contribution rate and the electron Since the dose is calculated for the region within the range of the electron beam by using the density distribution, there is an effect that the dose can be output in a short time while keeping the accuracy high.

Further, according to the invention described in claim (3), since the radiation treatment planning apparatus is configured such that a region having a high contribution rate is a target of calculation and the matrix size of the calculation is variable, the calculation accuracy is lowered so much. There is an effect that it is possible to obtain a high-speed dose output without having to do so.

[Brief description of drawings]

FIG. 1 is a block diagram showing a radiation treatment planning apparatus according to an embodiment of the invention described in claim (1), and FIG.
Fig. 3 is an explanatory diagram showing the relationship between X-rays and scattered X-rays, Fig. 3 is an explanatory diagram showing non-uniformity of electron density, Fig. 4 is an isodose diagram showing X-ray scattering distribution, and Fig. 5 is a horizontal line. 6 is a block diagram showing a radiation treatment planning apparatus according to an embodiment of the invention as set forth in claim (2), and FIG. 7 is a diagram showing the irradiated body divided into regions. FIG. 8 is an explanatory diagram showing how to divide, FIG. 8 is an explanatory diagram showing changes in the contribution rate, FIG. 9 is an explanatory diagram showing how X-rays are scattered, FIG. 10 is an explanatory diagram showing the direction of addition, and FIG. Is a block diagram showing a radiation treatment planning apparatus according to an embodiment of the invention described in claim (3), FIG. 12 is a distribution diagram showing a three-dimensional contribution distribution, and FIG. 13 is irradiating a human body with X-rays. Fig. 14 is an explanatory diagram showing the state, Fig. 14 is an explanatory diagram showing Compton scattering, Fig. 15 is an explanatory diagram for explaining the scattering process, and Fig. 16 is an electric current in the depth direction. Is an explanatory view showing the non-uniformity of density. 20, 21 and 22 are contribution distribution data sections, 23 and 24 are correction sections, 25 is a target area determination section, 26 is a calculation section, and 28 is a data section. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. An absorbed dose of radiation emitted from a radiation source to an irradiation target at a point of interest of the irradiation target, and an absorbed dose due to the radiation scattered at a point other than the point of interest; In the radiation treatment planning apparatus to calculate based on the absorbed dose caused by the electron beam generated by the radiation incident to other points, in the contribution distribution when the electron density in the irradiated body is uniform, The contribution distribution data part having a contribution distribution indicating the distribution of the contribution rate of the radiation to the attention point in the irradiated body, and the contribution rate of the portion of the contribution distribution from the attention point to the radiation source are The correction unit that corrects the electron density correction length of the irradiation body, and the contribution rate corrected by this correction unit multiplied by the electron density at each point corresponding to these contribution rates Radiation therapy planning apparatus is characterized in that an arithmetic unit to absorbed dose due to the scattered radiation definitive. 2. An absorbed dose of radiation emitted from a radiation source to an irradiation target at a point of interest of the irradiation target, and an absorbed dose due to the radiation scattered at points other than the point of interest, and In the radiation treatment planning apparatus to calculate based on the absorbed dose caused by the electron beam generated by the radiation incident to other points, in the contribution distribution when the electron density in the irradiated body is uniform, There is a contribution distribution data section having a contribution distribution showing a distribution of the contribution rate of the electron beam to the attention point in the irradiated object, and the attention point exists within a reach distance of the electron beam from the other point. In that case, it is determined that the point is in the target area, and the contribution rate is corrected by the electron density correction length of the irradiated body, and each point in the area determined by the correction section is corrected. Oh Radiation therapy planning apparatus is characterized in that an arithmetic unit to absorbed dose by the electron beam at the point of interest by adding the multiplied by the electron density at their respective points on the contribution rate of the electron beam that. 3. An absorbed dose of radiation emitted from a radiation source to an irradiation target at a point of interest of the irradiation target, and an absorbed dose due to the radiation scattered at points other than the point of interest, and In the radiation treatment planning apparatus that calculates based on the absorbed dose caused by the electron beam generated by the incidence of the radiation at another point, the contribution ratio of the scattered radiation or the generated electron beam to the attention point A contribution distribution data section having a contribution distribution indicating a distribution in the irradiated body, a region in the irradiated body that has a predetermined contribution rate or more in the contribution distribution, and a matrix size of calculation for this region are determined. The target area determination unit and the contribution ratio of the scattered radiation or electron beam at each point in the area determined by the target area determination unit Radiation therapy planning apparatus is characterized in that an arithmetic unit for adding the multiplied by the electron density point and absorbed dose by the scattered radiation or electron beam at the point of interest.