CN104318972A - Design method of X-ray flattening filter - Google Patents

Abstract

The invention relates to a design method of an X-ray flattening filter. A traditional design method of the flattening filter has the defects of being long in time consumed, high in cost and poor in flattening effect. The design of the multi-stage conical flattening filter is realized through the Monte Carlo method, a data fitting method and the like. The design method can realize a good flattening effect, and the whole process is clean and easy to realize. Meanwhile, the design cost is low and the design period is short.

Description

A kind of X ray expansion device method for designing

Technical field

The present invention relates to a kind of X ray expansion device method for designing, particularly for cone-beam x-ray, realize the method for designing of multi-stage taper expansion device based on the method such as Monte Carlo, data fitting.

Background technology

Traditional expansion device method for designing empirically designs the taper expansion device that is no more than three grades, and by revising expansion device structure repeatedly, test of many times reaches expansion effect after measuring.This method length consuming time, cost is high, and expansion effect is poor.

Also someone proposes a kind of expansion device method for designing.The method adopts the patten's design one generated step by step to have the expansion device of multistage frustum structure.Every one-level frustum all will through repeatedly adjusting, consuming time longer.In addition, due to the impact of ray scattering, often newly increase one-level frustum and all can frustum before be impacted.Therefore often newly-increased one-level frustum all needs to modify to frustum before, further increases the time of design, whole design need the number of times of amendment about to square being directly proportional of frustum quantity n.Along with the requirement of flatteness and the increase of frustum quantity, the global design time also will increase substantially.The design process of this method of formation is step by step also very complicated simultaneously.

Summary of the invention

In view of this, the object of the present invention is to provide a kind of X ray expansion device method for designing, the method realizes the design of multi-stage taper expansion device based on the method such as monte carlo method and data fitting.

For achieving the above object, the invention provides following technical scheme:

A kind of X ray expansion device method for designing, comprises the following steps:

1) X ray forms cone-beam x-ray after front collimation device, by place, expansion device bottom surface plane spatially angle be divided into n place, n is corresponding with expansion device frustum number, records each corresponding space angle θ ₁, θ ₂..., θ _n;

2) be the base of m at expansion device base place plane thickness setting, base and radiogenic distance are L; According to parameters such as x-ray source beam energy, target structures, monte carlo method is utilized to calculate X ray on expansion device base plane by step 1) the roentgen dose X A of the n position that divides and expansion device center ₀, A ₁... .., A _n, A ₀for the roentgen dose X at center place;

3) monte carlo method is utilized to calculate the power spectrum of X ray on this position, n+1 place:

$A_i=\underset{j=1}{\overset{k}{\mathrm{\Σ}}}{A}_{\mathrm{ji}},i=\mathrm{0,1,2},.....n$

4) design an one-level frustum, thickness is d ₀, make the dosage of center ray after the decay of this frustum with the roentgen dose X A of edge _nequal, A ₀'=A _n

5) wide beam modifying factor B is calculated

${A_0}^{\′}=A_n=B\underset{j=1}{\overset{k}{\mathrm{\Σ}}}{A}_{j0}{e}^{-{\mathrm{\μ}}_j{d}_0}$

Wherein, A _j0centered by ray energy spectrum component; μ _jfor the attenuation coefficient of correspondence; d ₀for frustum thickness, solve above-mentioned equation and can obtain wide beam modifying factor B;

6) the attenuation length d of each frustum is calculated _i

${A_i}^{\′}=A_n=B\underset{j=1}{\overset{k}{\mathrm{\Σ}}}{A}_{\mathrm{ji}}{e}^{-{\mathrm{\μ}}_j{d}_i}$

D _ifor the unique unknown number in formula, solve the attenuation length d that above-mentioned equation can obtain frustum at different levels _i;

7) according to the attenuation length d of frustum at different levels _iand the space angle θ of correspondence _icalculate the radius r of frustum at different levels _iwith thickness l _i;

8) according to the parameter r of frustum at different levels _iand l _iset up expansion device model, utilize monte carlo method to calculate the uniformity coefficient of ray after expansion device; Adjust the attenuation length d of frustum at different levels _i, the flatteness that analog computation is obtained reaches requirement;

9) process expansion device according to the later parameter of adjustment, expansion device is arranged on the position set and measures; If actual

Flatteness reaches requirement and does not then modify; If actual flatteness does not reach requirement, on this basis expansion device is slightly made an amendment, make the actual flatteness of ray reach requirement.

Further, the material that expansion device is used is metal material.

Further, the material that expansion device is used is copper or stainless steel.

Further, step 2) in X-ray energy scope from 50keV to 200MeV.

Further, step 7) in the radius r of frustum at different levels _iwith thickness l _iand the attenuation length d of frustum at different levels _iand the Space Angle θ of correspondence _ithere is following recurrence relation in degree:

θ ₀＝0

l _i＝d _i-1 cosθ _i-1-d _i cosθ _i,i＝1,2,....,n

$r_i=(L-d_0+\underset{j=1}{\overset{i}{\mathrm{\Σ}}}{l}_j)\tan {\mathrm{\θ}}_i,i=\mathrm{1,2},....,n.$

Further, step 1) to 8) in the foundation of roentgen dose X and power spectrum and expansion device model all at Geant4, or EGS, or other carry out based in the software of monte carlo method.

Beneficial effect of the present invention is: X ray expansion device method for designing provided by the invention can reach good expansion effect, and whole process flow is clear, is easy to realize; Meanwhile, design cost is lower, and the cycle is shorter.

Accompanying drawing explanation

In order to make object of the present invention, technical scheme and beneficial effect clearly, the invention provides following accompanying drawing and being described:

Fig. 1 is expansion device schematic diagram;

Fig. 2 is 6MeV medical accelerator expansion device structural section figure in embodiment;

Fig. 3 is the schematic flow sheet of the method for the invention.

Embodiment

Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail.

Fig. 1 is expansion device schematic diagram, and Fig. 3 is the schematic flow sheet of the method for the invention.

Be designed to example with 6MeV accelerator for electron therapy expansion device be specifically described the method for the invention, Fig. 2 is 6MeV medical accelerator expansion device structural section figure in the present embodiment, the technical requirement of this figure is: 1, cone boss portion size tolerance is by the processing of IT8 level, and all the other dimensional tolerences press the processing of IT10 level; 2, material is brass.

Specifically comprise the following steps:

1) the distance L=128mm of expansion device base distance radiographic source target spot, ray subtended angle is 14 °.The expansion device that one has 10 grades of frustum structures is set, the space angle θ that each frustum is corresponding _ibe respectively 1 °, 2 °, 3 °, 4 °, 5 °, 6 °, 8 °, 10 °, 12 °, 14 °.Expansion device Material selec-tion copper.

2) monte carlo method is utilized to calculate the dosage A of 6MeV ray in corresponding position ₀, A ₁... .., A ₁₀, A ₀for the roentgen dose X at center place.Calculate respective spectral distribution simultaneously.

$A_i=\underset{j=1}{\overset{60}{\mathrm{\Σ}}}{A}_{\mathrm{ji}},i=\mathrm{0,1,2},.....10$

3) designing a thickness is d ₀one-level frustum, make the dosage of the ray of center through frustum decay after equal with the roentgen dose X of edge.

A ₀′＝A ₁₀ d ₀＝20mm

4) wide beam modifying factor B is calculated

${A_0}^{\′}=A_{10}=B\underset{j=1}{\overset{60}{\mathrm{\Σ}}}{A}_{j0}{e}^{-{\mathrm{\μ}}_j{d}_0}$

5) attenuation length of frustum at different levels is calculated

${A_i}^{\′}=A_{10}=B\underset{j=1}{\overset{60}{\mathrm{\Σ}}}{A}_{\mathrm{ji}}{e}^{-{\mathrm{\μ}}_j{d}_i},i=\mathrm{1,2},...,10$

6) according to the attenuation length d of frustum at different levels _iand the space angle θ of correspondence _icalculate the radius r of frustum at different levels _iwith thickness l _i.

7) according to the parameter r of frustum at different levels _iand l _iset up expansion device model, utilize monte carlo method to calculate the uniformity coefficient of ray after expansion device.Adjust the attenuation length d of frustum at different levels _i, the flatteness that analog computation is obtained reaches requirement.

8) process expansion device according to the later parameter of adjustment, expansion device is arranged on the position set and measures.The basis of measurement result is once finely tuned expansion device structure, makes actual flatteness be less than 6%, as shown in Figure 3, reach designing requirement.

What finally illustrate is, above preferred embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although by above preferred embodiment to invention has been detailed description, but those skilled in the art are to be understood that, various change can be made to it in the form and details, and not depart from claims of the present invention limited range.

Claims (6)

1. an X ray expansion device method for designing, is characterized in that: comprise the following steps:

1) X ray forms cone-beam x-ray after front collimation device, by place, expansion device bottom surface plane spatially angle be divided into n place, n is corresponding with expansion device frustum number, records each corresponding space angle θ ₁, θ ₂..., θ _n;

2) be the base of m at expansion device base place plane thickness setting, base and radiogenic distance are L; According to parameters such as x-ray source beam energy, target structures, monte carlo method is utilized to calculate X ray on expansion device base plane by step 1) the roentgen dose X A of the n position that divides and expansion device center ₀, A ₁... .., A _n, A ₀for the roentgen dose X at center place;

3) monte carlo method is utilized to calculate the power spectrum of X ray on this position, n+1 place:

$A_i=\underset{j=1}{\overset{k}{\mathrm{\Σ}}}{A}_{\mathrm{ji}},i=\mathrm{0,1,2}.....n$

4) design an one-level frustum, thickness is d ₀, make the dosage of center ray after the decay of this frustum with the roentgen dose X A of edge _nequal, A ₀'=A _n

5) wide beam modifying factor B is calculated

${A_0}^{\′}=A_n=B\underset{j=1}{\overset{k}{\mathrm{\Σ}}}{A}_{j0}{e}^{-{\mathrm{\μ}}_j{d}_0}$

Wherein, A _j0centered by ray energy spectrum component; μ _jfor the attenuation coefficient of correspondence; d ₀for frustum thickness, solve above-mentioned equation and can obtain wide beam modifying factor B;

6) the attenuation length d of each frustum is calculated _i

$A_i^{\′}=A_n=B\underset{j=1}{\overset{k}{\mathrm{\Σ}}}{A}_{\mathrm{ji}}{e}^{-{\mathrm{\μ}}_j{d}_i}$

D _ifor the unique unknown number in formula, solve the attenuation length d that above-mentioned equation can obtain frustum at different levels _i;

7) according to the attenuation length d of frustum at different levels _iand the space angle θ of correspondence _icalculate the radius r of frustum at different levels _iwith thickness l _i;

8) according to the parameter r of frustum at different levels _iand l _iset up expansion device model, utilize monte carlo method to calculate the uniformity coefficient of ray after expansion device; Adjust the attenuation length d of frustum at different levels _i, the flatteness that analog computation is obtained reaches requirement;

9) process expansion device according to the later parameter of adjustment, expansion device is arranged on the position set and measures; If actual flatteness reaches requirement, do not modify; If actual flatteness does not reach requirement, on this basis expansion device is slightly made an amendment, make the actual flatteness of ray reach requirement.

2. a kind of X ray expansion device method for designing according to claim 1, is characterized in that: described expansion device material used is metal material.

3. a kind of X ray expansion device method for designing according to claim 2, is characterized in that: described expansion device material used is copper or stainless steel.

4. a kind of X ray expansion device method for designing according to claim 1, is characterized in that: step 2) in X-ray energy scope from 50keV to 200MeV.

5. a kind of X ray expansion device method for designing according to claim 1, is characterized in that: step 7) in the radius r of frustum at different levels _iwith thickness l _iand the attenuation length d of frustum at different levels _iand the Space Angle θ of correspondence _ithere is following recurrence relation in degree:

θ ₀＝0

l _i＝d _i-1cosθ _i-1-d _i cosθ _i,i＝1,2,....,n

$r_i=(L-d_0+\underset{j=1}{\overset{i}{\mathrm{\Σ}}}{l}_j)\tan {\mathrm{\θ}}_i,i=\mathrm{1,2},....,n.$

6. a kind of X ray expansion device method for designing according to claim 1, it is characterized in that: step 1) to 8) in the foundation of roentgen dose X and power spectrum and expansion device model all at Geant4, or EGS, or other carry out based in the software of monte carlo method.