CN100431485C - Method for determining distribution of electron beam dosage - Google Patents

Abstract

A method for determining the dose distribution of electronic beam includes such steps as using CT to measure the electronic density array of the irradiated object, measuring and recording the initial lateral parameters of electronic beam, its energy spectrum and the source-skin distance, debunching the irradiating electronic beam into an electronic microbeam array, calculating the 3D dose distribution of each microbeam in irradiated object, and adding all the electronic microbean arrays to obtain a 3D dose distribution array of an electronic beam in irradiated object.

Description

Determine the method that electron-beam dose distributes

Technical field

The present invention relates to the method that a kind of definite electron-beam dose distributes, be used for specifically, determine the electron beam method that 3-dimensional dose distributes in irradiated medium accurately at electron beam external exposure radiotherapy.

Background technology

The oncotherapy means of comparative maturity comprise operative treatment, radiotherapy and chemotherapy at present.Wherein radiotherapy has accounted for sizable ratio.Radiotherapy is specially adapted to partial tumor with certain profile.Implementing radiocurable prerequisite is to determine the position of tumor and judge the growth of tumor scope.This can be provided patient's 3 D anatomical information by computed tomography (CT), nuclear magnetic resonance, NMR (NMR) or positron emission computerized tomography technological means such as (PET).On this basis, the doctor determines tumor area (CTV) and sensitive organization (OARs), defines target area of irradiation (PTV) together with medical physicist again.Then, utilize radiotherapy treatment planning system to make patient's treatment plan.

In radiocurable clinical practice, determine that radiological dose is a basic problem.For fear of injury to normal structure, when electron beam shines, select conform irradiation, decide irradiation area according to tumor in the shape of electron beam incident direction exactly, the launched field right and wrong rule launched field that therefore forms.After irradiation area is determined, it need be dispersed and turn to a series of micro-electron beams, and form the intensity matrix of electron beam.At mid portion, the intensity of micro-electron beam is stronger; In the marginal portion, the intensity of micro-electron beam a little less than, determine according to practical situation.Outside the irradiated area, the intensity of micro-electron beam is 0.

The parameter of electron beam comprises the power spectrum of electron beam, the initial side direction parameter of electron beam and the SSD (source-skin distance) of irradiation.The initial side direction parameter of the power spectrum of electron beam and electron beam is by measuring.The SSD of irradiation determines according to the practical situation in when irradiation.

The algorithm of the definite electron-beam dose that uses comprises Monte Carlo method and analytical algorithm at present.The former comprises MMC (Macro Monte Carlo) method and VMC (Voxel Monte Carlo) method etc.For the computational accuracy that obtains to require, these two kinds of algorithms need a large amount of computation times, and this has limited their application clinically.And analytical algorithm is to grow up on the basis of Fermi-Eyges multiple-scattering theory, and such as pen beam model PBRA (Electron pencil-beam redefinition algorithm), but this method in use, needs a lot of measurement data.

Use hybrid pencil-beam model to obtain good precision and computational efficiency in the dose distribution under the regular illuminate condition, in even, non-uniform dielectric calculating electron beam.The inventive method uses hybrid pencil-beam model to calculate the 3-dimensional dose distribution of electron beam in human body or anthropoid medium, has the characteristics that measurement data is few, computational speed is fast, computational accuracy is high that need.

Summary of the invention

The objective of the invention is to: provide a kind of and can determine accurately that electron beam 3-dimensional dose in human body or anthropoid medium distributes, required measurement data is few, computational accuracy is high, the method that definite electron-beam dose of high efficiency distributes.

Technical scheme of the present invention is:

The method that a kind of definite electron-beam dose distributes is characterized in that comprising following steps:

A) adopt computed tomography (CT) to measure, draw the electron density matrix of irradiated object;

B) initial side direction parameter, electron beam power spectrum and the source-skin distance of surveying record irradiating electron beam;

C) irradiating electron beam being dispersed is electronics microbeam matrix;

D) and utilize hybrid pencil-beam model to calculate the 3-dimensional dose of each microbeam in irradiated object to distribute;

E) with the dose matrix addition of each electronics microbeam, the 3-dimensional dose distribution matrix of electron gain bundle in irradiated medium.

The invention has the beneficial effects as follows: use hybrid pencil-beam model to calculate the 3-dimensional dose of electron beam in human body or anthropoid medium and distribute, need that measurement data is few, computational speed is fast, computational accuracy is high.

Description of drawings

Fig. 1 is the design sketch of the test one of the specific embodiment of the invention.

Fig. 2 is the exposure experiment layout drawing of the test one of the specific embodiment of the invention.

Fig. 3 is the design sketch of the test two of the specific embodiment of the invention.

Fig. 4 is the exposure experiment layout drawing of the test two of the specific embodiment of the invention.

Fig. 5 is the particular flow sheet of working method of the present invention.

Fig. 6 is the electron beam precise radiotherapy system block diagram that adopts the inventive method.

The specific embodiment

The present invention is further described below in conjunction with drawings and Examples.

As shown in Figure 5, the method that definite electron-beam dose of the present invention distributes, according to following steps:

A) adopt computed tomography (CT) to measure, draw the electron density matrix of irradiated object;

B) initial side direction parameter, electron beam power spectrum and the source-skin distance of surveying record irradiating electron beam;

C) irradiating electron beam being dispersed is electronics microbeam matrix;

D) and utilize hybrid pencil-beam model to calculate the 3-dimensional dose of each microbeam in irradiated object to distribute;

E) with the dose matrix addition of each electronics microbeam, the 3-dimensional dose distribution matrix of electron gain bundle in irradiated medium.

Wherein, the parameter of electron beam comprises the power spectrum of electron beam, the initial side direction parameter of electron beam and the SSD (source-skin distance) of irradiation.The initial side direction parameter of the power spectrum of electron beam and electron beam is by measuring, and the practical situation of the SSD of irradiation during according to irradiation determined.

For fear of injury to normal structure, when electron beam shines, select conform irradiation, decide irradiation area according to tumor in the shape of electron beam incident direction exactly, the launched field right and wrong rule launched field that therefore forms.After irradiation area is determined, it need be dispersed and turn to a series of micro-electron beams, and form the intensity matrix of electron beam.

The concrete operation process of hybrid pencil-beam model is as follows:

Energy is that (cross-sectional sizes is that the vertical incidence of 2a * 2b) is at dielectric surface for the monoenergetic micro-electron beam of E.With the electron beam incident direction is z axle positive direction, is zero with the incidence point.The 3-dimensional dose that this micro-electron beam produces in medium is distributed as:

$D_p(x,y,z,E)=\frac{D_{\mathrm{bm}}(z,E)}{4}*[\mathrm{erf}\left(\frac{a+x}{\sqrt{A_2(z,E)}}\right)+\mathrm{erf}\left(\frac{a-x}{\sqrt{A_2(z,E)}}\right)]*$

$[\mathrm{erf}\left(\frac{b+y}{\sqrt{A_2(z,E)}}\right)+\mathrm{erf}\left(\frac{b-y}{\sqrt{A_2(z,E)}}\right)]$

D _p(x, y, z, E) the expression energy is the monoenergetic micro-electron beam of E, (x, y z) locate sedimentary energy (absorbed dose) in spatial point.D _Bm(z, E) the expression energy is the unlimited wide beam electronics of E, the sedimentary energy at the depth z place is calculated by two-group model.A and b are half of beam width of electron beam.A ₂(z, E) the expression energy is the micro-electron beam of E, the lateral distribution parameter at the depth z place.

$A_2(z,E)={\∫}_0^{z}T\left(E_t\right){(z-t)}^2\mathrm{dt}$

T(E _t)＝2σ _tr(E _t)

σ _Tr(E _t) be that energy is E _tThe transport cross-section of electronics.E _tBe that electronics is in the average energy at degree of depth t place when the energy of incident electron is E.

In the equation above, relate to calculating to error function erf (x).Because when calculating the 3-dimensional dose distribution, the calculating of error function will repeat many times, and the accurate Calculation of error function is relatively lost time.In the present invention, having calculated variate-value is error function value on 10,000 sample points between 1 to 2.In use, directly use the method for tabling look-up to obtain the error function value, thereby improved computational efficiency.

After electron beam is through the accelerator head, some electronic motion direction and energy will change.This change finally is reflected to the spatial dose distribution of electronics in medium.In order to consider this factor, the hybrid pencil-beam model correction to the lateral distribution CALCULATION OF PARAMETERS of electronics.Revised lateral distribution parameter is:

$A_2\left(z\right)={\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="C20061002270900112.png"\; state="\{\{state\}\}">A</figure-callout>}}_2^0+{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="C20061002270900112.png"\; state="\{\{state\}\}">A</figure-callout>}}_2^2\left(z\right)$

A ₂(z) be the revised lateral distribution parameter of electronic pen bundle at the depth z place.A ₂ ⁰Be the predose sectional parameter of electronic pen bundle, obtain in the flatness curve calculation of dielectric surface according to the electron beam of measuring.A ₂ ²(z) be that a beam electrons in the hybrid pencil-beam model is in the lateral distribution parameter at depth z place.

Consider the bendability of dielectric surface, the distance of the incidence point distance sources of each micro-electron beam all is different.Therefore, after electron beam was by discretization, the dose distribution of each micro-electron beam needed to revise, and to consider the influence of dielectric surface bending, its modifying factor is:

SSD ²/(SSD+d) ²

Behind the intensity matrix of having considered electron beam power spectrum, dielectric surface bending and electron beam (non-regular launched field), the 3-dimensional dose of electron beam in irradiated medium distributes and can be expressed as:

$D(x,y,z)=\underset{k}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}\underset{i}{\mathrm{\&Sigma;}}w\left(E_k\right)\frac{{\mathrm{SSD}}^2}{{(\mathrm{SSD}+d_{\mathrm{ij}})}^2}{a}_{\mathrm{ij}}{D}_p(x,y,z,i,j,k)$

In the following formula, (x, y z) are illustrated in point (x, y, dosage z) to D.I and j are that micro-electron beam after the discretization is in the numbering of x and y direction.K represents the numbering of incident beam power spectrum node.W (E _k) be that energy is E in the electron beam power spectrum _kThe weight of energy.d _IjIt is the surperficial corrected range that is numbered the micro-electron beam of ij.a _IjBe the intensity that is numbered the micro-electron beam of ij.D _p(x, y, z, i, j is to be numbered that energy is E in the power spectrum of micro-electron beam of ij k) _kPoint (x, y, z) dosage of Chan Shenging of electronics in medium.

According to the inventive method Measurement of Electron Beam dose distribution, wherein employed equipment and mutual relation are described below:

Computed tomography (CT): the anatomical information that obtains patient or irradiated object;

Electron beam therapy TPS system: accept patient or irradiated object information that the CT machine transmits.Under doctor's operation to patient's body surface, tumor, jeopardize organ and carry out three-dimensional reconstruction; Under physics teacher's operation, the irradiation plan is determined, provide the dose distribution and the DVH assessment data of irradiation plan;

Analog machine: simulate irradiation according to the irradiation plan;

Accelerator therapy machine: according to the irradiation plan patient is implemented irradiation by operator.

The annexation of each equipment as shown in Figure 6.Wherein, hybrid pencil-beam model calculates the 3-dimensional dose of each microbeam in irradiated object and distributes, and with the dose matrix addition of each electronics microbeam, the step of the 3-dimensional dose distribution matrix of electron gain bundle in irradiated medium is finished in electron beam therapy TPS system.

The implementation process of the inventive method is as follows:

1. patient carries out CT scan, obtains patient's CT data;

2. patient's CT data are input in the TPS system;

3. doctor's sketch outline, tumor and jeopardize organ;

4. physics Shi Liyong content of the present invention obtains the dose distribution of electron beam patient, obtains the treatment plan that can implement;

5. dose distribution and the DVH data such as (dosage-volume histograms) that should plan are also ratified through doctor's assessment, and patient simulated the location on analog machine, on accelerator patient is implemented irradiation by the staff then.

Specific embodiments of the invention are as follows:

Example one: irregular surfaces

The measurement data of this example is quoted ECWG (high-power electron beam treatment plan joint working group: experiment Collaborative Working Group contract on high energy electron beantreatment planning).In this experiment, use stair-stepping solid water anthropomorphic dummy external surface a precipitous stairstepping in irradiation field, to occur and change (as lower jaw).This example calculation under the illuminate condition of 100cmSSD, 15cm * 15cm launched field, the 20MeV electron beam is radiated at the dose distribution in the stepped solid water, as shown in Figure 2.Fig. 1 has provided the comparison of the isodose curve on the plane of decentre plane 1cm, and round dot is the measurement data of ECWG, and solid line is the measurement data of the inventive method.

Example two: non-regular launched field

The measurement data of this example is quoted the experiment of ECWG.In this experiment, designed " room shape " non-regular launched field, as shown in Figure 4.In this launched field, a long and narrow additament (chimney-like) and a triangle additament (roof shape) are arranged near central shaft, see Fig. 4.This example calculation under the illuminate condition of 100cmSSD, 15cm * 15cm launched field, the 20MeV electron beam is in the comparison of the isodose on the BEV plane of the 6.1cm degree of depth under the water tank surface under this launched field illuminate condition.Round dot is the measurement data of ECWG, and solid line is the measurement data of the inventive method, sees Fig. 3.

The foregoing description explanation is according to the electron beam distribution results of the present invention's measurement and the measurement result of ECWG, the actual distribution resultant error that is electron-beam dose is less, in allowing the scope of application, and measure the parameter of needed time and actual measurement, all the algorithm than traditional definite electron-beam dose lacks.

Claims (1)

1. method that definite electron-beam dose distributes is characterized in that comprising following steps:

The first step adopts computed tomography to measure the electron density matrix of irradiated object;

Second step, initial side direction parameter, electron beam power spectrum and the source-skin distance of surveying record irradiating electron beam;

In the 3rd step, it is electronics microbeam matrix that irradiating electron beam is dispersed, and utilizes hybrid pencil-beam model to calculate the 3-dimensional dose distribution of each microbeam in irradiated object;

$D_p(x,y,z,E)=\frac{D_{\mathrm{bm}}(z,E)}{4}*[\mathrm{erf}\left(\frac{a+x}{\sqrt{A_2(z,E)}}\right)+\mathrm{erf}\left(\frac{a-x}{\sqrt{A_2(z,E)}}\right)]*$

$[\mathrm{erf}\left(\frac{b+y}{\sqrt{A_2(z,E)}}\right)+\mathrm{erf}\left(\frac{b-y}{\sqrt{A_2(z,E)}}\right)]$

Wherein: D _Bm(z, E) the expression energy is the sedimentary energy of the unlimited wide beam electronics of E at the depth z place, calculate by two-group model,

A and b are half of beam width of electron beam,

A ₂(z, E) the expression energy is the lateral distribution parameter of the micro-electron beam of E at the depth z place,

$A_2(z,E)={\&Integral;}_0^{z}T\left(E_t\right){(z-t)}^2\mathrm{dt}$

T(E _t)＝2σ _tr(E _t)

σ _Tr(E _t) be that energy is E _tThe transport cross-section of electronics,

E _tBe that electronics is in the average energy at degree of depth t place when the energy of incident electron is E;

The 4th step, with the dose matrix addition of each electronics microbeam, the 3-dimensional dose distribution matrix of electron gain bundle in irradiated medium:

$D(x,y,z)=\underset{k}{\mathrm{\&Sigma;}}\underset{j}{\mathrm{\&Sigma;}}\underset{i}{\mathrm{\&Sigma;}}w\left(E_k\right)\frac{\mathrm{SS}{D}^2}{{(\mathrm{SSD}+d_{\mathrm{ij}})}^2}{a}_{\mathrm{ij}}{D}_p(x,y,z,i,j,k)$

In the formula: D (x, y, z) be illustrated in point (x, y, dosage z),

I and j are that micro-electron beam after the discretization is in the numbering of x and y direction

K represents the numbering of incident beam power spectrum node

W (E _k) be that energy is E in the electron beam power spectrum _kThe weight of energy,

d _IjBe the surperficial corrected range that is numbered the micro-electron beam of ij,

a _IjBe the intensity that is numbered the micro-electron beam of ij,

D _p(x, y, z, i, j is to be numbered that energy is E in the micro-electron beam power spectrum of ij k) _kPoint (x, y, z) dosage of Chan Shenging of electronics in medium.

Images