JPH03297476A - Radiotherapy planning device - Google Patents

Abstract

PURPOSE:To decrease the quantity of operations performed at a computing portion by correcting the distribution of contributions in the direction leading from an aimed point to a radiation source according to the corrected length of electron density between the point and the source, and providing the distribution of contributions to the computing portion after the distribution is corrected. CONSTITUTION:A radiotherapy planning device is provided with a contribution distribution data portion 20 having the distribution of contributions indicating how the contribution factors of scattered radioactive rays to an aimed point are distributed in a subject to be irradiated, a correcting portion 23 for correcting according to the corrected length of electron density of the subjected to be irradiated the contribution factors of that portion of the distribution of contributions which leads from the aimed point to a radiation source, and a computing portion 26 which adds values obtained by multiplication of the contribution factors by electron densities at each point corresponding to the contribution factors after the factors are corrected by the correcting portion 23, so as to find the quantity of absorbed radioactive rays resulting from radioactive rays scattered at the aimed point. The time required for calculation can thus be shortened to a practical time while minimizing an error of calculated dosage with respect to the actual dosage.

Description

[Detailed Description of the Invention] (Industrial Application Field) - This invention relates to a radiation treatment planning device that calculates the absorbed dose of radiation in an irradiated body during radiation treatment using a medical linac or a cobalt-60 gamma ray therapy machine. It is.

[Conventional technology]

Figure 13 shows how X-rays are irradiated to the affected part of the human body (object to be irradiated).
FIG. 2 is an explanatory diagram showing a situation in which radiotherapy is being performed. In the figure, 30 is X-ray line # (radiation #), 32 is the patient (human body)
, 34 is the affected area of the patient, and 36 is the X-ray irradiation width.

As shown in FIG. 14, most of the X-rays 38 incident on the human body 32 undergo Compton scattering. In other words, -X-ray 38
At the same time, the X-rays are scattered and become scattered rays 42, and the scattering vA42 reduces the energy by the amount of energy given to the electrons. , which is a phenomenon in which the wavelength becomes longer. Note that at this time, the scattering angle β of the electron m40 is 90° or less.

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

By the way, when treating the patient 32 using the X-rays 38, it is necessary to know the dose to the affected area 34.

How much linear motion X to cause the necessary damage to the colored part 34?
This is because it is necessary to determine whether the line 38 should be irradiated. Therefore, there is a need for a radiation treatment planning device that performs the amount calculation. Conventional radiation therapy planning devices use the Monte Carlo method, the Conpollou Noyon method, the delta volume method, and the equivalent tissue air ratio (ET A R; Eq
uivalent Ti5sue AirRatio
) Law, Power Criminal Law, Scatter Air Ratio (ScatterAir
Dose calculations were performed using the Ratio method, RTAR method, etc.

The Monte Carlo method is a method in which calculations without three-dimensional approximation are repeated until sufficient accuracy is obtained through simulation, and the most accurate line 1 distribution can be obtained, but even when using the IMIPS calculator as a radiation treatment planning device, 8
It takes more than an hour. In order to shorten this calculation time, in the convolution method, the contribution distribution of the dose to other points due to scattering at a certain point is calculated, and this is calculated for all the points hit by X-rays. Dose distribution is determined by adding up the points. In addition, in the delta volume method, the direct rays, primary scattered rays, and other scattered rays to the point of interest are divided and multiplied in three dimensions. On the contrary,
In the ETAR method, two-dimensional integration is performed by renormalizing the influence of three-dimensional scattered radiation onto a two-dimensional equivalent plane. As shown in FIG. 16, the power criminal law has a density ρ3. ρ2
This is a correction method when there are layers of non-uniformity. Here, reference numeral 46 indicates a point of interest in the attention area 44. The RTAR method is a method that utilizes the fact that when the ratio of the area of the irradiation field and the perimeter as seen from the line a30 side is equal, the TAR is equal. The SAR method converts the contribution of scattered radiation into an equivalent radiation field radius based on the shape of the radiation field.
This is a method of pulling an AR table.

Note that radiation treatment planning devices using each of the above methods are generally realized using a computer program. In addition, when performing each calculation, tomographic images obtained by X-ray CT are widely used, and the electron density corresponding to the X-ray energy is calculated from both CT images a-light and used.

Regarding radiation treatment planning devices using each of the above methods, please refer to Computer Application
cation in Radiation Thera
pyTreatment Planning Radi
ation Medicine), Volume 1, No. 2,
James A Purd
y), described in detail in 1983.

[Problem to be solved by the invention: Since the conventional radiation treatment planning device is configured as described above, the one that calculates the contribution of scattered radiation by three-dimensional calculation is
It takes a lot of calculation time and cannot be applied to actual radiation therapy.
In addition, calculations using two-dimensional calculations cannot adequately handle the non-uniformity of electron density and the irregular shape of the irradiation field.
CRU (International Comm1ti
on on Radiation Unitsand
There was a problem in that it was not possible to perform dose calculations under all conditions that would satisfy the recommendation of Mesuremer Hs, that is, to keep the error in the administered dose to 5% or less. For example, when the ETAR method is used, an error of 7% or more may occur.

This invention was made to solve the above problems, and provides a radiation treatment planning device that can shorten calculation time to a practical time while minimizing the error between the calculated dose and the actual dose. The purpose is to obtain.

[Means for solving the problem] The radiation therapy planning device according to the invention described in claim (1) comprises:
The contribution distribution data part has a contribution distribution that shows the distribution of the contribution rate of scattered radiation to the point of interest in the irradiated object, and the contribution rate of the portion of the contribution distribution from the point of interest to the radiation source is calculated based on the electrons of the irradiated object. a correction section that corrects with a density correction length;
and a calculation unit that adds the product of the contribution factors corrected by the correction unit by the electron density at each point corresponding to these contribution factors to obtain the absorbed dose due to the scattered radiation at the pressure point. It is something that

The radiation therapy planning device according to the invention described in claim (2) further includes a contribution distribution data section having a contribution distribution indicating a distribution in the irradiated body of the contribution rate of the generated electron beam to the point of interest, and If a point of interest exists within the reachable distance of the electron beam from and an arithmetic unit that calculates the absorbed dose due to the scattered electron beam at the point of interest by adding the contribution rate of the electron beam at each point in the area of interest multiplied by the electron density at each point. .

The radiation therapy planning device according to the invention described in claim (3) is provided with a contribution distribution data section having a contribution distribution indicating a distribution in the irradiated body of the contribution rate of the scattered radiation or the electron beam generated by the scattering to the point of interest. , a target area determination unit that determines a region in the irradiated body where the contribution distribution has a predetermined contribution rate or more and a calculation parasitic size for this region, and a target in area determination unit that determines a The absorbed dose due to the scattered radiation or electron beam at the point of interest is obtained by adding the contribution rate of the scattered radiation or electron beam at each point in the area multiplied by the electron density of each part. It is equipped with a calculation section.

[For production]

The correction unit in the invention described in claim (1) corrects the contribution distribution in the direction from the point of interest to the radiation source using the electron density correction length therebetween, and provides the corrected contribution distribution to the calculation unit, thereby The invention according to claim (2), characterized in that the calculation amount of electrons in the arithmetic unit is made to be a The target area determining unit in the invention according to claim (3), which is characterized by a region that targets other points when reaching a point, and excludes other points, for example, refers to both CT images. Then, a region in which the contribution rate of the scattered radiation or electron beam to the point of interest is greater than or equal to a predetermined value is determined, and this region is provided to the calculation section as a calculation target region. In addition, the calculation efficiency is optimized by varying the calculation matrix size according to the slope of the contribution distribution.

(Embodiment) Hereinafter, an embodiment of the invention as claimed in claim (1) will be described with reference to the drawings. In FIG. A contribution distribution data section 23 stores a contribution distribution indicating the contribution rate of X-rays (scattered rays) scattered at each point of the portion hit by the line to the point of interest 46; A correction unit corrects the contribution rate using the density correction length, a calculation unit 26 calculates the dose due to scattered radiation from the output contribution distribution and the electron density at each point, and 28 stores the electron density, etc. at each point. It should be noted that the contribution distribution stored in the contribution distribution data section 20 can be determined through experiments or calculations.

Next, the operation will be explained. FIG. 2 shows how X-rays 38 are incident on an X-ray absorber such as a human body, scattered at point A (scattering point), and incident on a point of interest 46. Note that the point of interest 46 will be referred to as point B hereinafter. At this time, the proportion (contribution rate) of the scattered rays 42 contributing to point B among the scattered X-rays can be expressed by the following equation.

ηx (d, θ; +r;) −exp (−μ+d;L・
・・・・・・・・・ (1) Here, μ is the average X-ray absorption coefficient at d, f(θ
) is the probability that X-rays are scattered at an angle of θ by Compton scattering, and C is a coefficient. Furthermore, equation (1) can be rewritten as follows.

exp (-μmd, -μ2ri) ・・・・・・・・・ (2) Here, if μ, −μ2, that is, if the absorption coefficient in the human body is constant, then μ+di−〃zr; ”'−μ( dl + r,)
-1 μId +, r, (1-cosθ,))...
(2) For example, using 4MV X-ray 38, u = 0.03/
cm, rl=7cm, θ=251+, ex
p(-gr(1-cos θ)l = 0.98, and if θ is even smaller, even if -μd in -μd1-μr1, the error in (1) 2 is less than 2%. The smaller the error, the smaller the error.In this case, (3) is obtained.

Next, the case where μm≠μ2, that is, the absorption coefficient is non-uniform in the depth direction, will be explained with reference to the third article. The contribution rate due to A1 is exp (-μ, d μ2 (d dI)-μzr1) exp (-μ, d μzdllIII 2rl (1-cosθ...
(4) In the human body, the absorption coefficient is approximately proportional to the electron density ρ, so μ1dl−μzdo= #(ρldl÷ρzdn)mitta (5). Here, D is an electron density correction length obtained by correcting the depth of the human body in the direction of the radiation source up to point B by density.

- morphologically (if the degree of heterogeneity is more multi-layered)
, ■−Σρ;ds (N=l, Il, III
,...). From equations (4) and (5), exp (u'l uzr+(l cosθi))
・・・・・・・・・ (6) )) is obtained.

Therefore, At θ minus 25°, Because it is, ・・・・・・・・・(7) However, equation (7) is A, the contribution rate via point.

Next, considering the contribution rate via point A2, exp (tt
Ding u? ' (1 cos θ2)) (9) Here, the general formula includes ? −Σρ,r,.

(9) also holds when θ2 is 25 degrees, where: ...... (8) ...... (10). Therefore, from equations (6) and (9), generally, 2-μldl μZdll μ+ (daZ) 2-μad (μ+(d+ dz) +μzdI+1”X+'
(/17 uF+ (1-cosθ-))...
...(■1) If θ is 〈25°, then...
...(12) becomes.

From the above, the correction unit 23 has the contribution distribution data unit 20
From, the contribution distribution when the electron density is uniform (Habo (12)
Corresponds to the expression. ), it is sufficient to perform correction using the electron density correction length using the density within the human body 32 and output the corrected contribution distribution (corresponding to equation (11)). In the conventional case, density correction corresponding to equation (1) was performed.

Then, the calculation unit 26 may perform the following calculation to calculate the dose due to the scattered radiation at point B. Here, ρ(i, jk)
is the electron density of each part expressed in (i, j, k) coordinates by dividing the computational head into equal parts, and ηxb(i, j, k) is (11
) The expression expressed in 2 is applied to each part. Further, the value of ρ(i, j, k) is roughly stored in the data section 28.

By the way, the scattering distribution of X-rays due to Compton scattering (f
(θ)) is the fourth
As shown in the figure, since they are concentrated in the front, when θ is large, f(θ) is small where r is large. Therefore, the effect of the term exp (u 7; (1-cosθ, )) is small, so for such a part, (12)
You may also use formulas. Note that if you calculate the matrix, you can add exp (-μm) or ex
It is possible to obtain η□ by simply multiplying by p (−μμ−μ7; (]−cosθ, )).

(11) Calculation by 2 is very simple compared to (1) 2, and is the fastest and easiest calculation for an electronic computer, so a normal electronic computer was applied to the radiation treatment planning device. In case, ru. In addition, in the conventional radiation therapy planning apparatus, the calculation according to equation (1) is executed for the entire region. Further, the calculation unit 26 executes a three-dimensional calculation, or the above-described method can also be applied to a two-dimensional calculation.

As shown in FIG. 5, there may be non-uniformity in the electron density ρρ2 in the i direction, but in order to correct this non-uniformity, (
Equation 11) or Equation (12) may be corrected as follows. In other words, equation (11) or (12)
In the formula, 1-μ? in eXp(-μ?, (l cosθ,)) ;
Multiply by (1coSθ,) ・・・・・・・・・(1G). Therefore, eXp(u (?+7+(1cosθ,)...
...(15) is obtained. In this way, non-uniformity in the i direction can also be corrected. Also, exp [-μ(cho, 1-raw-・汀, 2
)) i2 may be set as exp (-μ(7□-d, □)). However, in this case, an error occurs when the X-ray is incident obliquely, but the error is small at a point with a large contribution rate (a point closer to point B).

Also, in equation (15), tt7r(1-cos θ
, ) is small, it can be approximated as ...... (]7). In this way, calculation time can be further reduced. The error when approximating in this way is
It is less than 1% under real conditions and is sufficiently practical. Also, in equation (16)? 8 is? , −ΣΣΣρ＜ ,
, j, k> d (cos θ1 given by i Wayuri takes some calculation time. Therefore, it may be done as follows. Here, COS θ is calculated in advance for each matrix.

FIG. 6 is a block diagram showing a radiation treatment planning apparatus according to an embodiment of the invention as claimed in claim (2).

In Fig. 6, 12 is a radiation treatment planning device, and 2I is an electron beam (direct beam) generated from each point behind the part of the human body that is exposed to X-rays when the electron density is uniform.B
A contribution distribution data section 24 stores a contribution distribution indicating a contribution rate contributing to a point, and a contribution distribution data section 24 defines a boundary between a point where an electron beam from that point reaches point B and a point where it does not among each point, and serves as a calculation target. 26 is a correction unit that determines the area and corrects the contribution rate using the electron density correction length; 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; 28 is a calculation unit for each point. This is a data section that stores information such as electron density.

Next, the operation will be explained. Figure 7 shows the human body 32 at 5mm.
An example is shown in which the corners are divided into cubic areas. The contour lines in the figure indicate lines where the contribution rate η5 of the electron beam to point B is equal. The incident X-ray 38 has a contribution rate η, −0,
The electron beam that causes scattering at point A of 01 and enters point B is
The electron density at point A is ρ.

Then, ρ, ηb =0.01ρ4. Therefore, the dose due to all electron beams (total direct beams) to the region of interest (B iJr region) including point B, b, is given by: Here, ρ(i, j, k) is (i, j, k)
Cubic electron density in coordinates, η.

(i, j, k) is the contribution rate of the electron beam from the (i, j, k) cube to the B region.

By the way, the addition in equation (19) is ηb(i, jk)
It is only necessary to perform this for the region >0.001. This is because, as shown in FIG. 8, the electron beam has a predetermined range (reachable range), and contributions from outside the point ηb <0.01 disappear immediately outside.

Here, the contribution distribution of the electron beam in the human body 32 changes depending on the electron density ρ. In particular, the contribution distribution in the actual human body 32 is approximately determined by the density of the B region and the cube in the direction of the radiation source. Therefore, if we find the correlation between the distribution of η and the distribution of ρ(i, j, k) as shown in Figure 8, we can find the distribution of η from the distribution of ρ(i, j, k). be able to. In particular, η can be predicted simply by looking at the change in the j direction of ρ(i, j, k).

Therefore, the data section 28 stores the distribution of ρ(i, j, k), that is, the distribution of the electron density, and also stores the contribution rate of the electron beam corresponding to the electron density. Then, the correction unit 24 can determine the contribution distribution of the electron beam in consideration of the electron density in the human body 32 from the distribution of the electron density in the J direction and the contribution rate of the electron beam corresponding to the electron density. At this time, the range of ρ(i, j, k) to be targeted is determined in consideration of the calculation accuracy and calculation time required in the calculation unit 26. The range may be within the range of the electron beam.

By determining the calculation target range in the calculation section 26 in this manner, the calculation time of the calculation section 26 can be further shortened.

By the way, the contribution rate of the electron beam can be expressed as follows when the X-ray is scattered at point A as shown in FIG. 9. Here, d is the electron density correction length mentioned above, ■=Σd, ρ= , g (7; , R(E) ) is the range R(E) of the electron beam when the X-ray energy is E.
The range function determined by 7(?-Σr, ρ8) as already mentioned, and f(θ) is the probability that the X-ray is scattered at the angle of θ, as already mentioned. Therefore, calculate and allocate 0,·f(θ,) in equation (20) for the (i, j, k) cube, and also 1^ for each (i, j, k) cube. Calculate, create a table, and extract each data from the table.
It is also possible to determine η by simply calculating , .

In addition, as a method of determining the target area, it is possible to add ρ from point B in the direction of the radiation source 30, and set the target area to a point that becomes range R(E). It is advisable to prepare several types of η depending on the X-ray energy E and the electron density. η.

The distribution of g (
7, R(E) ), and in the part where θ is large, f
It is determined by (θ, ). Therefore, the change in electron density is θ
, is a small part, and the above determination method is a good short answer.

Also, as shown in Figure 1O, the electron density is added in a predetermined order up to the range R (snake), and ? At this time, find the weight W, (iWb (i, j, k)) for point B of each (ij, k) cube,
It is also possible to derive η corresponding to this ρ□, or to directly use the dose D e b.

Then, when finding η in equation (20), ? , -Da
It may be set to +9br. Here, ρ,,ρ.

Make the cube corresponding to . What if I do it like this? , can be calculated in a shorter time.

FIG. 11 is a block diagram showing a radiation treatment planning apparatus according to an embodiment of the invention as claimed in claim (3).

In FIG. 11, 14 is a radiation treatment planning device, and 22 is a contribution rate at which scattered rays at each point in the part of the human body 32 that is hit by X-rays contributes to point B, or a direct line from each point to point B. A contribution distribution data part 25 in which a contribution distribution indicating a contribution rate is determined is a boundary between a point where the contribution rate to point B is equal to or higher than a predetermined value and a point where it is not based on both CT images. A target area determining unit 26 determines the dose due to scattered radiation or direct radiation from the contribution distribution and the electron density at each point for the target area. This is a calculation unit that calculates the resulting dose. Further, 28 is a data section in which information such as electron density at each point is stored.

Next, the operation will be explained. Figure 12 shows three isolines showing the contribution distribution of the scattered rays 42 or electron beams 40 to point B.
It is shown in dimensions. In the figure, point P and point Q indicate the same point. As is clear from the figure, on the ij plane, points that are the same distance from point B have the same contribution rate to point B. In addition, in the direction, only points above 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. 12. In addition, the numerical value is for explanation and not quantitatively accurate.In this case, the target area determining unit 25 uses the CT image (12th
In the figure, slices 51 to 55 are shown. ) is used to determine areas with high contribution rates. For example, the contribution rate η is 0.
Determine the area where the value is 0001 or more. In FIG. 12, the region of interest is between the portions of slices 52 and 54 indicated by double lines. The calculation unit 26 inputs the contribution data from the contribution distribution data unit 22, inputs the electron density manually from the data unit 28, multiplies the area determined by the target area determination unit 25 by a corresponding value, and calculates the result. Add it up, calculate the dose, and output it. Generally, calculations are performed by dividing the target region into small regions, that is, (i, j, k) regions ((i, j,
k) indicates a coordinate, and lj is a natural number). Therefore,
Perform the calculation as follows.

Here, ρ(i, j, k) is the electron density in the (i, j, k) region, and ηb (+, J, k) is the contribution rate of the (1j, k) region. The calculation target is ηゎ(i, j, k)≧
This is about the area of 0.001.

Conventionally, calculations were performed on the entire area within the boxes (B), (C), and (D) in FIG. 12. Note that the density of the area between the slices 52 and 54 can also be determined by interpolation. In this way, by limiting the target area,
Even when three-dimensional calculation is performed, calculation time can be shortened.

Note that the contributions of the other slices 52 and 54 may be renormalized to a certain slice 53 at point B (indicated by a broken line in FIG. 12(B)). First, the line 1iD by slice N (N is the slice number) is determined as follows.

Here, (i, j, k) is the area on slice N.

At this time, D is obtained as follows.

Db −Σ Dbs Ws ・・
(23) Here, WN is each (i, j,
k) It is a factor that converts the area into the ratio of the actual irradiation field volume and adjusts the absolute value of D. If each (i, j, k) area is divided into equal parts, Db = W Σ D, ・・・・
...... (24). If you do this, 3
Dimensional calculations can be performed in several times the time of two-dimensional calculations. On the other hand, if "" and "k" each take a value from 1 to 40, in the conventional case, it took 40 times as long as the two-dimensional calculation. Note that in the conventional radiation therapy planning apparatus using the ETAR method, accurate renormalization based on such contribution distribution is not taken into consideration when renormalizing three-dimensional contributions into two-dimensional ones, and errors may be large.

In addition, the size of the (i, j, k) region is used depending on the slope of the contribution distribution, and where the slope is small, the size of the (i, j, k) region is
) The size of the 6N area may be increased. This can further reduce calculation time while preventing deterioration in accuracy. For example, in equation (23), in slices 52 and 54 other than slice 53 including point B, the gradient of the contribution distribution to point B is small. Therefore, calculations are performed as follows using a wide size.

D, -Σ DbN 匈, ・・・・・・
(25) (Tap, J3<Wsz=Wsn) Here, the ratio of W53 to W,2 is taken to correct the volume ratio. In other words, the target area determination unit 25 increases the size of the portion Q where the slope of the contribution distribution is small. In addition, the size may be changed even within the same slice depending on the slope of the contribution distribution. Furthermore, it may be applied to the size when determining the electron density between slices using interpolation.

In addition, TPR (li!, S
A PR value may also be used. Here, the depth is d and the illumination depth is d.

is obtained from ηb (i, j, k). Also, the correction radius r. is obtained from ro-ρ,,r. ρ. is. That is, DC-d-TPR (d, l, r, , ), (d is a constant). DC is the dose at the isocenter.

In this way, variations in the TPR values of the devices due to differences in manufacturers can be suppressed without correcting η, (i, j, k). Also, ρ. , d, , can be compared with ρ, d to check for errors in the calculation. Here, instead of TPR value, TAR value or PD
A D value or the like may also be used. The TPR value is the Mi woven mafanthom 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 contribution rate can be calculated using equation (21),
(23) may be used, and the cotton amount due to the region with a low contribution rate may be calculated from the SPR value. In other words, ......(27) In equation (27), the first term on the right side is ηb (i, j, k
)≧0.01, the second term is 0.01 >η, (i, j
, k) is a term related to a region of 0.0001, and a is a coefficient including a field factor. Note that SPR is the scattering peak dose ratio.

Note that most of the calculations performed by the calculation unit 26 are based on addition, so when an electronic computer is used as the radiation treatment planning device, the calculations can be performed at high speed because they can be performed using fixed-point calculations. The conventional ETAR method requires floating point calculations due to the large number of exponent calculations and divisions, which takes a considerable amount of calculation time.

[Effects of the Invention] As described above, according to the invention described in claim (1), the radiation treatment planning device uses the electron density correction length to estimate the scattered radiation when the given electron density is uniform. Since the configuration is configured such that the contribution rate of is corrected and the dose is calculated using the contribution rate and the electron density distribution, it is possible to output the dose in a short time while maintaining high accuracy.

Further, according to the invention described in claim (2), the radiation therapy planning device corrects the contribution rate of the electron beam when the given electron density is uniform by calculating the electron density correction length, and calculates the contribution rate and Since the dose is calculated for a region within the range of the electron beam using the electron density distribution, it is possible to output the dose in a short time while maintaining high accuracy.

Furthermore, according to the invention S described in claim (3), the radiation treatment planning device is configured so that a region with a high contribution rate is the target of calculation and the matrix size of the calculation is variable.
This has the effect of being able to output doses at high speed without significantly reducing calculation accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a radiation treatment planning device according to an embodiment of the invention as claimed in claim (1), and the second figure is a diagram showing the incident X.
Figure 3 is an explanatory diagram showing the relationship between X-rays and scattered X-rays, Figure 3 is an explanatory diagram showing the non-uniformity of electron density, Figure 4 is a contour diagram showing the scattering distribution of X-rays, and Figure 5 is a horizontal diagram An explanatory diagram showing the non-uniformity of electron density, FIG.
Figure 8 is an explanatory diagram showing how to divide the irradiated object into regions.
FIG. 9 is an explanatory diagram showing the change in contribution rate, FIG. 9 is an explanatory diagram showing the state of scattering of XvA, FIG. 10 is an explanatory diagram showing the direction of addition, and No. 110 is an explanatory diagram showing the direction of addition. Figure 12 shows the radiation treatment planning device according to the embodiment.
A distribution diagram showing the contribution distribution of dimensions, Figure 13 is an explanatory diagram showing how the human body is irradiated with X-rays, Figure 14 is an explanatory diagram showing Compton scattering, and Figure 15 is an explanatory diagram to explain the scattering process. FIG. 16 is an explanatory diagram showing the non-uniformity of electron density in the depth direction. 20 21 , 22 are contribution distribution data sections, 2324 is a correction section, 25 is a target area determination section, 26 is a calculation section, and 28 is a data section. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) The absorbed dose of the radiation irradiated from the radiation source to the irradiated body at a point of interest on the irradiated body is divided into the absorbed dose due to the radiation scattered at other points other than the point of interest, and the absorbed dose due to the radiation scattered at other points other than the point of interest. In a radiation treatment planning device that calculates based on the absorbed dose caused by an electron beam generated when the radiation is incident on a point, the contribution distribution when the electron density in the irradiated body is uniform, a contribution distribution data section having a contribution distribution indicating the distribution of the contribution rate for the point of interest in the irradiated body; A correction section corrects the electron density correction length using the electron density correction length of 1. A radiation treatment planning device comprising: a calculation unit that calculates absorbed dose due to radiation. (2) The absorbed dose of the radiation irradiated from the radiation source to the irradiated body at a point of interest on the irradiated body is divided into the absorbed dose due to the radiation scattered at other points other than the point of interest, and the absorbed dose due to the radiation scattered at other points other than the point of interest. In a radiation treatment planning device that calculates based on the absorbed dose due to an electron beam generated by the incidence of the radiation at a point, the contribution distribution when the electron density in the irradiated body is uniform, a contribution distribution data section having a contribution distribution indicating a distribution of a contribution rate of a line to the point of interest in the irradiated object; and when the point of interest exists within a reachable distance of the electron beam from the other point , a correction unit that determines that the point is within the target area and corrects the contribution rate using the electron density correction length of the irradiated object; and an electron beam at each point in the area determined by the correction unit. a calculation unit that adds the contribution factor multiplied by the electron density at each point to obtain the absorbed dose by the electron beam at the point of interest. (3) The absorbed dose of the radiation irradiated from the radiation source to the irradiated body at a point of interest on the irradiated body is divided into the absorbed dose due to the radiation scattered at other points other than the point of interest, and the absorbed dose due to the radiation scattered at other points other than the point of interest. In a radiation treatment planning device that calculates based on an absorbed dose due to an electron beam generated by the incidence of the radiation at a point, the contribution rate of the scattered radiation or the generated electron beam to the point of interest is calculated. a contribution distribution data section having a contribution distribution indicating a distribution in the irradiated body; a region in the irradiated body where the contribution rate is equal to or higher than a predetermined contribution rate in the contribution distribution; and a target region for determining a matrix size for calculation for this region. and a determining unit, which adds the contribution rate of the scattered radiation or electron beam at each point in the area determined by the target area determining unit multiplied by the electron density at each point, and calculates the result at the point of interest. A radiation treatment planning device comprising: a calculation unit that calculates the absorbed dose due to the scattered radiation or the electron beam.