CN104502947A - Device and method for quickly obtaining development-free verification film dose response curve - Google Patents

Abstract

The invention belongs to a method for quickly obtaining a radiographic development-free verification film dose response curve in an ion beam spot scanning irradiation technology. A device for quickly obtaining a development-free verification film dose response curve is mainly characterized in that an X-direction scanning magnet, a Y-direction scanning magnet, a collimator, a reference monitor ionization chamber and a position sensitive detector are arranged on a beam line in sequence respectively, wherein a pencil beam passes through the X-direction scanning magnet, the Y-direction scanning magnet, a collimating hole of the collimator and the reference monitor ionization chamber on a beam line in sequence to acquire a pencil beam flow in normal Gaussian distribution at an isocenter. The device and the method have the advantages that (1) the measurement preparation work of operators can be reduced and the beam flow use time and the subsequent film data processing time can be reduced by using a development-free verification film dose calibration method, and (2) infinite data points can be theoretically obtained in Gaussian pencil beam transverse dose distribution and development-free verification film light intensity distribution, so that more data can be selected to perform data fitting to obtain the more accurate film dose response curve.

Description

The apparatus and method of quick acquisition flushing-free checking film dosimetry response curve

Technical field

The invention belongs to the method for a kind of quick acquisition radiography flushing-free checking film dosimetry response curve in ion beam spot scanning irradiation technique.

Background technology

In Ion beam application (as radiobiology experiment, Material Physics, radiation therapy etc.), usually relate to the measurement to ion beam irradiation field characteristic, as radiation field dose uniformity or dosage distribution measuring.Utilize ionization chamber matrix directly can measure these characteristics, but ionization chamber space of matrices resolution is low, be difficult to meet measure ion beam spot or dose gradient larger field dose distribution requirement.The dosage distribution that irradiation field measured by radiography film has the high advantage of spatial resolution, and particularly the appearance of flushing-free checking film, makes the method utilizing film to measure become easier.Compared with conventional developer film, flushing-free checking film does not need to use chemical reagent to carry out development and fixing, can operate under visible light, decrease human intervention process, reduce measuring error.Further, flushing-free checking film can cut into some fritters and carry out irradiation development respectively, improves the effective rate of utilization of film.In addition, flushing-free checking film has water proofing property, can be placed in water tank, measure the irradiation field characteristic at different depth place simultaneously.In view of above-mentioned many merits, the application of flushing-free checking film in radiation dose measurement is more and more extensive.But, utilize flushing-free to verify film measuring radiation field characteristic, first need to carry out dose calibration experiment to film, obtain the relation of film optical density (or gray scale) change and irradiation dose, i.e. dose response curve.

In typical X-ray Intensity Modulation Radiated Therapy (IMRT), generally need that the dosage distribution obtained is calculated to treatment planning systems and carry out experimental verification, to assess the feasibility for the treatment of plan.In ion beam spot scanning beam delivery, same needs measures the dosage distribution of each irradiation field.For ensureing the spatial resolution measuring dosage distribution, in confirmatory measurement, usually utilizing radiography flushing-free to verify at present, Film Dosimeter measures the dosage distribution of each irradiation field.By special software, flushing-free is verified that the grey scale change of film converts dosage distribution measuring value to, and distribute to compare with the dosage that planning system calculates and calculate γ percent of pass, to assess the feasibility for the treatment of plan.Before adopting flushing-free checking film to measure dosage distribution, usually need to measure the film dosimetry response curve obtaining respective batch in advance.At present, the conventional method brief operation step of this preliminary experiment is as follows:

1) utilize professional scanner (e.g., EPSON10000XL) to scan one whole flushing-free checking film, obtain red channel pixel value and distribute and calculate pixel average

2) whole flushing-free checking film is cut into several fritters, utilize Uniform Irradiation field to irradiate different dosage D respectively to every fritter flushing-free checking film;

3) scanner is again utilized to obtain each fritter flushing-free postradiation checking film red channel average pixel value

4) formula (A1) is utilized to calculate the clean optical density value of each fritter flushing-free checking film,

$\mathrm{netOD}={\mathrm{OD}}_{\mathrm{irr}}-{\mathrm{OD}}_{\mathrm{unirr}}={\log }_{10}\left(\frac{{\stackrel{\‾}{\mathrm{PV}}}_{\mathrm{unirr}}-{\mathrm{PV}}_{\mathrm{bckg}}}{{\stackrel{\‾}{\mathrm{PV}}}_{\mathrm{irr}}-{\mathrm{PV}}_{\mathrm{bckg}}}\right),---\left(A1\right)$

Wherein, netOD, OD _irrand OD _unirrbe respectively clean optical density, optical density and pre-irradiation optical density after film irradiates; PV _bckgfor opaque black plastic plate red channel pixel value;

5) according to dosage D and the clean optical density value netOD of the irradiation of each fritter flushing-free checking film, data analyzing and processing software is utilized to obtain the dose response curve of flushing-free checking film.

In the active spot scan beam delivery system of ion beam, beam monitoring is different with the difference of ion beam energy, pencil beam bundle spot size and analyzing spot spacing with reference to the Dose calibration factor of ionization chamber.If under active spot scan beam delivery system, utilize the dose response curve of conventional method scale film, first, need establishment spot scan radiation parameters control documents, a uniform irradiation field is formed to hundreds and thousands of analyzing spot pointwise illumination and carries out the dose calibration of beam monitoring with reference to ionization chamber, obtain the Dose calibration factor, as shown in Figure 2.Then, work out a series of control documents and irradiate a series of fritter film respectively, thus obtain the postradiation film of various dose.Visible active spot scan beam delivery system obtains uniform irradiation field and to obtain homogeneous X-ray irradiation field unlike ion beam passive type beam delivery system and clinac so convenient, needs the time more grown.Want to obtain more data point to obtain meticulousr film dosimetry response curve, need cut less by film or use more film, such irradiation time can extend, and film needs the more time to be used in film scanning after irradiating.Obvious this film scale technical process is loaded down with trivial details, length consuming time, and the utilization factor of film is low.

Summary of the invention

The object of the invention is to, for avoiding the deficiencies in the prior art, providing a kind of device of quick acquisition flushing-free checking film dosimetry response curve.

Another object of the present invention is to provide a kind of method of quick acquisition flushing-free checking film dosimetry response curve.

Loaded down with trivial details for scale radiography film process under the active beam delivery system of ion beam, length consuming time, and the problem such as film effective rate of utilization is low, the present invention utilizes active spot scan beam delivery technical characterstic and beam transmission characteristic, proposes a kind of method of quick scale flushing-free checking film dosimetry response curve.The method utilizes ion beam spot direct scale flushing-free checking film, obtain its dose response curve, decrease the number of times forming homogeneous radiation open country under active spot scan beam delivery system, reduce the total number of ions needed for whole scale process, thus greatly reduce irradiation time and film substrate processing time, and whole flushing-free checking film can be cut into and be used for scale and measurement compared with the film of small size simultaneously, improve the effective rate of utilization of film.

The dose response curve of radiography film is usually used in the dosage distribution of measuring radiation field.The present invention adopts its inverse process, and the physical dosage namely by irradiating known distribution to flushing-free checking film obtains its dose response curve.The present invention makes full use of pencil beams to be had transversely dosage and is tending towards the feature of Gaussian distribution in transmitting procedure, first measure the distribution parameter of this Gauss's pencil beam, the pencil beam spot recycling this Gaussian distribution irradiates flushing-free checking film, obtains the change of its pixel value or clean optical density (netOD) distribution.Then utilize dosage to distribute change or netOD distribute with pixel value, acquisition flushing-free verifies the dose response curve of film.Acquisition ion beam Gauss's pencil beam spot and the distribution of its physical dosage are keys of the present invention.Under normal circumstances, the form of a stroke or a combination of strokes line that ion accelerator provides is not exclusively Gaussian, or accelerator data can be regulated the regularization of form of a stroke or a combination of strokes line by circular collimating aperture, be obtained the form of a stroke or a combination of strokes line (as Fig. 1) of positive gauss distribution by aerial multiple scattering effect.Utilize the absolute physical dosage distribution that directly can obtain Gauss's pencil beam spot through the bidimensional ionization chamber matrix of dose calibration, but due to its spatial resolution low, be difficult to the measurement requirement met in practical application.The method substituted is, utilize position sensitive detector as high-resolution multiwire proportional chamber, itemize ionization chamber or bidimensional ionization chamber matrix, first obtain the relative physical dosage distribution of Gauss pencil beam spot, then its two-dimensional phase can be obtained by Gauss model matching physical dosage is distributed.The absolute physical dosage distribution of pencil beam spot is derived according to the number of ions irradiated.Brief operation of the present invention can be summarized as operating process as shown in Figure 3.

For achieving the above object, the technical scheme that the present invention takes is: a kind of device of quick acquisition flushing-free checking film dosimetry response curve, its principal feature is in beam line, to be respectively equipped with X successively to sweeping magnet, Y-direction sweeping magnet, collimating apparatus, reference monitor ionization chamber, position sensitive detector; Pencil beam successively by collimating aperture, the reference monitor ionization chamber of X to sweeping magnet, Y-direction sweeping magnet, collimating apparatus, is waiting the form of a stroke or a combination of strokes line of center acquisition positive gauss distribution in beam line.

Described position sensitive detector is high-resolution multiwire proportional chamber, itemize ionization chamber or two-dimentional ionization chamber matrix.

A method for described quick acquisition flushing-free checking film dosimetry response curve, its principal feature is step:

(1) obtain with reference to ionization chamber counting and number of ions relation, i.e. ion beam active spot scan beam delivery system Dose calibration factor K (E) value:

Under the active spot scan beam delivery system of ion beam, Dose calibration need measure the relation obtaining MU and number of ions, that is,

K(E)＝N/MU， (1)

Wherein, K (E) is often corresponding with reference to ionization chamber counting number of ions; N is the number of ions irradiating single analyzing spot;

MU is the reference ionization chamber counting irradiating single analyzing spot;

Because dose value D and number of ions N has following relation:

Wherein, D is dose value; N is the number of ions irradiating single analyzing spot; S is ion mass stopping power in media as well; A is the area of single analyzing spot;

In spot scan Dose calibration, use form of a stroke or a combination of strokes line to form uniform enough large irradiation field waiting center, namely each analyzing spot irradiates identical reference ionization chamber and counts (MU); Therefore, have:

$K\left(E\right)=N/\mathrm{MU}=\frac{D_{\mathrm{meas}}}{1.6\×{10}^{-8}\·S_E\left(z\right)\·\mathrm{MU}}\mathrm{\Δx\Δy},---\left(3\right)$

Wherein, D _measfor the dose value that absolute dosages ionization chamber is measured at irradiation field center; S _ez (), for demarcating the mass of ion stopping power at degree of depth z place, utilizes Bethe-Bloch formulae discovery to obtain; Δ x, Δ y are analyzing spot spacing in x and y directions;

(2) by collimating aperture or regulate accelerator by the regularization of form of a stroke or a combination of strokes line, the multiple scattering of line in air act on wait center obtain positive gauss distribute form of a stroke or a combination of strokes line;

(3) utilize position sensitive detector to obtain the X of Gauss's pencil beam spot, the relative dosage distribution in Y-direction, recycling Gaussian function fitting, obtains its relative dosage distribution parameter σ _x, σ _y;

(4) distribution of bundle spot absolute physical dosage is obtained:

Measured by step (1) and step (3) and obtain K (E) value and bundle spot Gaussian Distribution Parameters σ _x, σ _y, derive bundle spot physical dosage distribution D (x, y) when waiting center to irradiate specific reference ionization chamber counting MU, that is:

$D(x,y;x_0,y_0)=\frac{1.6\×{10}^{-8}\·S\·\mathrm{MU}\·K\left(E\right)\·\exp [-\frac{{(x-x_0)}^2}{2{\mathrm{\σ}}_x^2}-\frac{{(y-x_0)}^2}{2{\mathrm{\σ}}_y^2}]}{2\mathrm{\π}{\mathrm{\σ}}_x{\mathrm{\σ}}_y},---\left(4\right)$

Wherein, x ₀, y ₀for bundle spot center; S is mass stopping power;

(5) the flushing-free checking film utilizing Film scanner to scan label orientation and cut, obtains film red channel average pixel value

(6) flushing-free is verified that film perpendicular fasciculus flow path direction such as to be placed at the center, arrange suitable reference ionization chamber counting (MU), the Gaussian bundle spot utilizing step (2) to obtain irradiates; After film fully exposes 24h, scanner is again utilized to obtain film red channel pixel value distribution PV _irr(x, y); After utilizing formula (5) to obtain irradiation, film is clean

(7) optical density distribution;

$\mathrm{netOD}(x,y){\mathrm{OD}}_{\mathrm{irr}}(x,y)-{\mathrm{OD}}_{\mathrm{unirr}}(x,y)={\log }_{10}\left(\frac{{\stackrel{\‾}{\mathrm{PV}}}_{\mathrm{unirr}}-{\mathrm{PV}}_{\mathrm{bckg}}}{{\mathrm{PV}}_{\mathrm{irr}}(x,y)-{\mathrm{PV}}_{\mathrm{bckg}}}\right),---\left(5\right)$

Wherein, netOD, OD _irrand OD _unirrbe respectively clean optical density, optical density and pre-irradiation optical density after film irradiates; PV _bckgfor opaque black plastic plate red channel pixel value; Utilize two-dimensional Gaussian function to carry out matching to the clean optical density distribution of two dimension, obtain the central point (x of the clean optical density distribution of film ₀, y ₀), thus obtain netOD (x, y, x ₀, y ₀) distribution function;

(8) corresponding physical dosage D (x, y, x is obtained according to formula (4) to MU value set during this film of irradiation ₀, y ₀) distribution function, compare netOD (x, y, x finally by data processing tools ₀, y ₀) and D (x, y, x ₀, y ₀) distribution function obtain flushing-free checking film dose response curve.

The installation method of described quick acquisition flushing-free checking film dosimetry response curve, also comprises step:

(9) step (5) is repeated to step (7), select several reference ionization chamber counting varied in size to irradiate several pieces of flushing-frees respectively and verify that films obtain the dose response curve of multiple dosage range, merge these dose response curves to obtain the wider more reliable response curve of dosage range.

The method of described quick acquisition flushing-free checking film dosimetry response curve, described step (3) is:

Utilize two-dimentional ionization chamber matrix, obtain the X of Gauss's pencil beam spot, the relative dosage distribution in Y-direction, recycles multiple Gaussian function fitting, obtains its relative dosage fitting of distribution parameter w _i, σ _xi, σ _yi(i=1 ..., n), wherein, w _iit is the weight of i-th Gaussian function _,meet Σ w _i=1; σ _xi, σ _yibe respectively the parameter of i-th gauss of distribution function;

The method of described quick acquisition flushing-free checking film dosimetry response curve, described step (4) is:

Obtain the distribution of bundle spot absolute physical dosage:

Measured by step (1) and step (3) and obtain K (E) value and bundle spot distribution parameter w _i, σ _xi, σ _yi, bundle spot absolute physical dosage distribution D (x, y) when waiting center to irradiate specific reference ionization chamber counting MU can be derived, that is:

$D(x,y;x_0,y_0)=\frac{1.6\×{10}^{-8}\·S\·\mathrm{MU}\·K\left(E\right)}{2\mathrm{\π}}\underset{i}{\mathrm{\Σ}}\frac{w_i}{{\mathrm{\σ}}_{\mathrm{xi}}{\mathrm{\σ}}_{\mathrm{yi}}}\exp [-\frac{{(x-x_0)}^2}{2{\mathrm{\σ}}_{\mathrm{xi}}^2}-\frac{{(y-x_0)}^2}{2{\mathrm{\σ}}_{\mathrm{yi}}^2}],---\left(4\right)$

Wherein, x ₀, y ₀for bundle spot center; S is mass stopping power.

The method of described quick acquisition flushing-free checking film dosimetry response curve, pixel value directly can be adopted in described step (6) to change the data processing method of the clean optical density of replacement calculating, then in step (7), obtain the relation curve of pixel value change and dosage as film dosimetry response curve.

Beneficial effect of the present invention: (1) adopts flushing-free provided by the invention to verify film dosimetry scale method, can reduce the measurement preliminary work of operating personnel, reduce line service time and follow-up film data processing time.Conventional radiography film dosimetry scale method is utilized to obtain film dosimetry response curve, first need to carry out prescan to whole film, obtain background image data file, then film is cut into many fritters, different dosage is irradiated to every block film, such as, 0.0,0.1,0.2,0.3,0.4,0.5,0.7,1.0,1.5,2.0,3.0,4.0,5.0,6.0,7.0,8.0Gy.After film fully develops, above-mentioned fritter need be placed in scanner center respectively and scan for reducing the distribute error brought of scanner light source, acquisition a series of images data file.This work is quite loaded down with trivial details.And utilizing method provided by the invention, whole film only need cut into 2 to 4 fritters in advance, sweeps in advance respectively to these several pieces of films, and then carrying out bundle spot to these several pieces of films irradiates different MU and count, and after film fully develops, then scans postradiation film.Due to much fewer than classic method of the block number of whole film cutting, even can cut, therefore the corresponding meeting of the time of film scanning is shortened greatly, the working load of experiment operator can be alleviated, and because the center dosage distribution of restrainting spot is higher, therefore can greatly reduce the accumulated dose of irradiation, reduce line service time; (2) infinite multiple data point can be obtained in theory in the distribution of Gauss's pencil beam transverse dosage and the distribution of flushing-free checking film optical density, therefore can choose more data and carry out data fitting and obtain film dosimetry response curve more accurately.

Accompanying drawing illustrates:

Fig. 1 Gaussian bundle spot relative dosage distribution measuring schematic diagram;

In figure: 1 sweeping magnet; 2 pencil beams; 3 collimating apparatuss; 4 with reference to monitor ionization chamber; 5 Gaussian bundle spots; 6 position sensitive detectors; 7 beam line;

Fig. 2 active spot scan Dose calibration schematic diagram;

Fig. 3 flushing-free checking film bundle spot scale measurement procedure figure;

Fig. 4 obtains the distribution of X-direction actual physics dosage;

Fig. 5 obtains film pixel value distribution in X-direction;

The EBT2 flushing-free that Fig. 6 adopts the inventive method and classic method to obtain verifies film dosimetry response curve.

Embodiment

Below in conjunction with accompanying drawing shownschematically preferred example be described in further detail:

Embodiment 1: a kind of device of quick acquisition flushing-free checking film dosimetry response curve, beam line 7 is respectively equipped with X successively to sweeping magnet 1-1, Y-direction sweeping magnet 1-2, collimating apparatus 3, reference monitor ionization chamber 4, position sensitive detector 6; Pencil beam 2 in beam line 7 successively by X to sweeping magnet 1-1, Y-direction sweeping magnet 1-2, collimating apparatus 3 collimating aperture, with reference to survey ionization chamber 4.Described position sensitive detector is high-resolution multiwire proportional chamber.

Embodiment 2: the device of described quick acquisition flushing-free checking film dosimetry response curve, described position sensitive detector is itemize ionization chamber.All the other are identical with embodiment 1.

Embodiment 3: the device of described quick acquisition flushing-free checking film dosimetry response curve, described position sensitive detector is two-dimentional ionization chamber matrix.All the other are identical with embodiment 1.

Embodiment 4: a kind of method of quick acquisition flushing-free checking film dosimetry response curve, the steps include:

(1) obtain with reference to ionization chamber counting and number of ions relation, i.e. ion beam active spot scan beam delivery system Dose calibration factor K (E) value:

Under the active spot scan beam delivery system of ion beam, Dose calibration need measure the relation obtaining MU and number of ions, that is,

K(E)＝N/MU， (1)

Wherein, K (E) is often corresponding with reference to ionization chamber counting number of ions; N is the number of ions irradiating single analyzing spot;

MU is the reference ionization chamber counting irradiating single analyzing spot;

Because dose value D and number of ions N has following relation:

D[Gy]＝1.6×10 ^-8×S[MeV/g·cm ^-2]×N/A[mm ^-2]， (2)

Wherein, D is dose value; N is the number of ions irradiating single analyzing spot; S is ion mass stopping power in media as well; A is the area of single analyzing spot;

In spot scan Dose calibration, use form of a stroke or a combination of strokes line to form uniform enough large irradiation field waiting center, namely each analyzing spot irradiates identical reference ionization chamber and counts (MU); Therefore, have:

$K\left(E\right)=N/\mathrm{MU}=\frac{D_{\mathrm{meas}}}{1.6\×{10}^{-8}\·S_E\left(z\right)\·\mathrm{MU}}\mathrm{\Δx\Δy},---\left(3\right)$

Wherein, D _measfor the dose value that absolute dosages ionization chamber is measured at irradiation field center; S _ez (), for demarcating the mass of ion stopping power at degree of depth z place, utilizes Bethe-Bloch formulae discovery to obtain; Δ x, Δ y are analyzing spot spacing in x and y directions;

(2) by collimating aperture by the regularization of form of a stroke or a combination of strokes line, the multiple scattering of line in air such as to act at the form of a stroke or a combination of strokes line that center obtains positive gauss distribution;

(3) utilize position sensitive detector to obtain the X of Gauss's pencil beam spot, the relative dosage distribution in Y-direction, recycling Gaussian function fitting, obtains its relative dosage distribution parameter σ _x, σ _y:

(4) distribution of bundle spot absolute physical dosage is obtained:

Measured by step (1) and step (3) and obtain K (E) value and bundle spot Gaussian Distribution Parameters σ _x, σ _y, derive bundle spot physical dosage distribution D (x, y) when waiting center to irradiate specific reference ionization chamber counting MU, that is:

$D(x,y;x_0,y_0)=\frac{1.6\×{10}^{-8}\·S\·\mathrm{MU}\·K\left(E\right)\·\exp [-\frac{{(x-x_0)}^2}{2{\mathrm{\σ}}_x^2}-\frac{{(y-x_0)}^2}{2{\mathrm{\σ}}_y^2}]}{2\mathrm{\π}{\mathrm{\σ}}_x{\mathrm{\σ}}_y},---\left(4\right)$

Wherein, x ₀, y ₀for bundle spot center; S is mass stopping power;

(5) the flushing-free checking film utilizing Film scanner to scan label orientation and cut, obtains film red channel average pixel value

(6) flushing-free is verified that film perpendicular fasciculus flow path direction such as to be placed at the center, arrange suitable reference ionization chamber counting (MU), the Gaussian bundle spot utilizing step (2) to obtain irradiates; After film fully exposes 24h, scanner is again utilized to obtain film red channel pixel value distribution PV _irr(x, y); Utilize formula (5) to obtain and irradiate the clean optical density distribution of rear film;

$\mathrm{netOD}(x,y){\mathrm{OD}}_{\mathrm{irr}}(x,y)-{\mathrm{OD}}_{\mathrm{unirr}}(x,y)={\log }_{10}\left(\frac{{\stackrel{\‾}{\mathrm{PV}}}_{\mathrm{unirr}}-{\mathrm{PV}}_{\mathrm{bckg}}}{{\mathrm{PV}}_{\mathrm{irr}}(x,y)-{\mathrm{PV}}_{\mathrm{bckg}}}\right),---\left(5\right)$

Wherein, netOD, OD _irrand OD _unirrbe respectively clean optical density, optical density and pre-irradiation optical density after film irradiates; PV _bckgfor opaque black plastic plate red channel pixel value; Utilize two-dimensional Gaussian function to carry out matching to the clean optical density distribution of two dimension, obtain the central point (x of the clean optical density distribution of film ₀, y ₀), thus obtain netOD (x, y, x ₀, y ₀) distribution function;

(7) corresponding physical dosage D (x, y, x is obtained according to formula (4) to MU value set during this film of irradiation ₀, y ₀) distribution function, compare netOD (x, y, x finally by data processing tools ₀, y ₀) and D (x, y, x ₀, y ₀) distribution function obtain flushing-free checking film dose response curve.

(8) because the impact of large angle scattering and secondary fragment can occur ion beam in transmitting procedure, single two-dimensional Gaussian function is usually adopted completely truly can not to reflect the absolute physical dosage distribution of ion beam spot edge cold spot area, especially

(9) be at dimensional Gaussian dosage distribution peaks 15% with lower area, there are differences with actual value.Therefore step (5) can be repeated to step (7), select the individual suitable reference ionization chamber the varied in size counting of 2-3 to irradiate 2-3 block flushing-free and verify that film obtains the dose response curve of multiple dosage range, merge these dose response curves to obtain the wider more reliable response curve of dosage range.

Embodiment 5: the method for the device of described quick acquisition flushing-free checking film dosimetry response curve, the steps include:

(1) identical with embodiment 4 step (1);

(2) identical with embodiment 4 or embodiment 6 step (2);

(3) utilize two-dimentional ionization chamber matrix, obtain the X of Gauss's pencil beam spot, the relative dosage distribution in Y-direction, recycles multiple Gaussian function fitting, obtains its relative dosage fitting of distribution parameter w _i, σ _xi, σ _yi(i=1 ..., n), wherein, w _ibe the weight of i-th Gaussian function, meet Σ w _i=1; σ _xi, σ _yibe respectively the parameter of i-th gauss of distribution function;

(4) distribution of bundle spot absolute physical dosage is obtained:

Measured by step (1) and step (3) and obtain K (E) value and bundle spot distribution parameter w _i, σ _xi, σ _yi, bundle spot absolute physical dosage distribution D (x, y) when waiting center to irradiate specific reference ionization chamber counting MU can be derived, that is:

$D(x,y;x_0,y_0)=\frac{1.6\×{10}^{-8}\·S\·\mathrm{MU}\·K\left(E\right)}{2\mathrm{\π}}\underset{i}{\mathrm{\Σ}}\frac{w_i}{{\mathrm{\σ}}_{\mathrm{xi}}{\mathrm{\σ}}_{\mathrm{yi}}}\exp [-\frac{{(x-x_0)}^2}{2{\mathrm{\σ}}_{\mathrm{xi}}^2}-\frac{{(y-x_0)}^2}{2{\mathrm{\σ}}_{\mathrm{yi}}^2}],---\left(4\right)$

Wherein, x ₀, y ₀for bundle spot center; S is mass stopping power;

(5) identical with embodiment 4 step (5);

(6) identical with embodiment 4 step (6);

(7) identical with embodiment 4 step (7).

Embodiment 6: the method for described quick acquisition flushing-free checking film dosimetry response curve, the steps include:

(1) identical with embodiment 4 step (1);

(2) by regulate accelerator by the regularization of form of a stroke or a combination of strokes line, the multiple scattering of line in air act on wait center obtain positive gauss distribute form of a stroke or a combination of strokes line;

(3) identical with embodiment 4 or embodiment 5 step (3);

(4) identical with embodiment 4 or embodiment 5 step (4);

(5) identical with embodiment 4 or embodiment 5 step (5);

(6) identical with embodiment 4 or embodiment 5 step (6);

(7) identical with embodiment 4 or embodiment 5 step (7);

(8) if step (3) and step (4) identical with embodiment 4 step (3) and step (4), then identical with embodiment 4; If step (3) and step (4) identical with embodiment 5 step (3) and step (4), then this step can be omitted.

Embodiment 7: the method for described quick acquisition flushing-free checking film dosimetry response curve, the steps include:

(1) identical with embodiment 4 step (1);

(2) identical with embodiment 4 or embodiment 6 step (2);

(3) identical with embodiment 6 step (3);

(4) identical with embodiment 6 step (4);

(5) identical with embodiment 6 step (5);

(6) flushing-free is verified that film perpendicular fasciculus flow path direction such as to be placed at the center, arrange suitable reference ionization chamber counting (MU), the Gaussian bundle spot utilizing step (2) to obtain irradiates; After film fully exposes 24h, scanner is again utilized to obtain film red channel pixel value distribution PV _irr(x, y); Utilize formula (5) to obtain and irradiate rear film pixel change profile;

ΔPV(x,y)＝|PV _irr(x,y)-PV _unirr|， (5)

Utilize two-dimensional Gaussian function to carry out matching to two-dimensional pixel value change profile, obtain the central point (x of film pixel value change profile ₀, y ₀), thus obtain Δ PV (x, y, x ₀, y ₀) distribution function;

(7) corresponding physical dosage D (x, y, x is obtained according to formula (4) to MU value set during this film of irradiation ₀, y ₀) distribution function, compare Δ PV (x, y, x finally by data processing tools ₀, y ₀) and D (x, y, x ₀, y ₀) distribution function obtain flushing-free checking film dose response curve;

(8) identical with embodiment 6 step (8).

Checking example 1: see Fig. 1,

It is carry out on the HIRFL (HIRFL) of the CAS Institute of Modern Physics that this checking example is measured.For verifying the feasibility of the inventive method, examples measure adopts classic method and the inventive method to obtain the dose response curve of EBT2 flushing-free checking film (second generation EBT flushing-free checking film) respectively, as shown in Figure 6.

The experiment of the dose response curve of classic method scale EBT2 film is (according to active beam delivery system based on passive type beam delivery system, then each irradiation is measured all needs to form uniform irradiation open country at active beam delivery system), utilize 250MeV/u carbon ion beam to carry out.Gas-monitoring carries out calibrated scale with reference to the Physical Absorption dosage that the every MU of ionization chamber (self-control) is corresponding under experimental conditions by absolute dosages ionization chamber (Markus-23343, German PTW company).Get an EBT2 film to utilize professional scanner (Epson expression10000XL) to scan to obtain after original image data file, mark film orientation be cut into EBT2 film in parts 16 fritters, distribution be placed on wait center irradiation 0.0,0.1,0.2,0.3,0.4,0.5,0.7,1.0,1.5,2.0,3.0,4.0,5.0,6.0,7.0,8.0Gy dosage.After film fully develops (about 24h), each fritter film is placed on scanner central scan according to the orientation of scanning whole film and obtains view data.Utilize special software analysis and process film image data, obtain the netOD value under corresponding exposure dose, thus obtain the dose response curve of EBT2 film.

The experiment of the dose response curve of the inventive method scale EBT2 film utilizes 250MeV/u carbon ion beam, carries out based on active spot scan beam delivery system.First, what carry out is that gas-monitoring is with reference to the experiment of ionization chamber dose calibration.Experiment condition is carbon ion beam stream energy 250MeV/u, pencil beam bundle spot FWHM is about 10mm, Δ x and Δ y is 2mm, and scanning obtains the circular irradiation field that diameter is 6cm, irradiates the Markus-23343 ionization chamber being placed in circular irradiation field center at carbon ion beam Bragg curve Ping Qu.By formula (4) and heavy ion mass stopping power (mass stopping power, stopping power professional term) theoretical calculation formula, obtain K ≈ 1050.Pencil beam bundle spot size is increased by regulating the mode of accelerator magnet parameter and scattering, the bundle spot waiting center to obtain approximate Gaussian distribution, utilize two-dimentional ionization chamber matrix (2D-Array seven29, PTW company of Germany) measure bundle spot size, obtain horizontal direction bundle spot σ=22.48mm.Keep beam status, the EBT2 film perpendicular fasciculus stream incident direction one whole being obtained raw image data be placed on wait center, irradiate reference ionization chamber 10 ⁷the dosage of individual counting, after about 24h, again scans this film and obtains postradiation film image data.For simplicity, in this checking example, taking-up bundle spot X-direction physical dosage distribution (Fig. 4) and film X-direction gradation data (Fig. 5) carry out Data Analysis Services.Finally obtain the dose response curve of this film, result as shown in Figure 6.Found by two kinds of method contrasts, the dose response curve that the inventive method and classic method obtain EBT2 film is consistent, thus confirms the feasibility of the inventive method.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (7)

1. obtain a device for flushing-free checking film dosimetry response curve fast, it is characterized in that in beam line, being provided with X respectively successively to sweeping magnet, Y-direction sweeping magnet, collimating apparatus, reference monitor ionization chamber, position sensitive detector; Pencil beam successively by collimating aperture, the reference monitor ionization chamber of X to sweeping magnet, Y-direction sweeping magnet, collimating apparatus, is waiting the form of a stroke or a combination of strokes line of center acquisition positive gauss distribution in beam line.

2. the device obtaining flushing-free checking film dosimetry response curve fast as claimed in claim 1, is characterized in that described position sensitive detector is high-resolution multiwire proportional chamber, itemize ionization chamber or two-dimentional ionization chamber matrix.

3. the method obtaining flushing-free checking film dosimetry response curve fast as claimed in claim 1, is characterized in that step:

(1) obtain with reference to ionization chamber counting and number of ions relation, i.e. ion beam active spot scan beam delivery system Dose calibration factor K (E) value:

Under the active spot scan beam delivery system of ion beam, Dose calibration need measure the relation obtaining MU and number of ions, that is,

K(E)＝N/MU， (1)

Wherein, K (E) is often corresponding with reference to ionization chamber counting number of ions; N is the number of ions irradiating single analyzing spot;

MU is the reference ionization chamber counting irradiating single analyzing spot;

Because dose value D and number of ions N has following relation:

D[Gy]＝1.6×10 ^-8×S[MeV/g·cm ^-2]×N/A[mm ^-2]， (2)

Wherein, D is dose value; N is the number of ions irradiating single analyzing spot; S is ion mass stopping power in media as well; A is the area of single analyzing spot;

In spot scan Dose calibration, use form of a stroke or a combination of strokes line to form uniform enough large irradiation field waiting center, namely each analyzing spot irradiates identical reference ionization chamber and counts (MU); Therefore, have:

$K\left(E\right)=N/\mathrm{MU}=\frac{D_{\mathrm{meas}}}{1.6\×{10}^{-8}\·S_E\left(z\right)\·\mathrm{MU}}\mathrm{\Δx\Δy},---\left(3\right)$

Wherein, D _measfor the dose value that absolute dosages ionization chamber is measured at irradiation field center; S _ez (), for demarcating the mass of ion stopping power at degree of depth z place, utilizes Bethe-Bloch formulae discovery to obtain; Δ x, Δ y are analyzing spot spacing in x and y directions;

(2) by collimating aperture or regulate accelerator by the regularization of form of a stroke or a combination of strokes line, the multiple scattering of line in air act on wait center obtain positive gauss distribute form of a stroke or a combination of strokes line;

(3) utilize position sensitive detector to obtain the X of Gauss's pencil beam spot, the relative dosage distribution in Y-direction, recycling Gaussian function fitting, obtains its relative dosage distribution parameter σ _x, σ _y;

(4) distribution of bundle spot absolute physical dosage is obtained:

Measured by step (1) and step (3) and obtain K (E) value and bundle spot Gaussian Distribution Parameters σ _x, σ _y, derive bundle spot physical dosage distribution D (x, y) when waiting center to irradiate specific reference ionization chamber counting MU, that is:

$D(x,y;x_0,y_0)=\frac{1.6\×{10}^{-8}\·S\·\mathrm{MU}\·K\left(E\right)\·\exp [-\frac{{(x-x_0)}^2}{2{\mathrm{\σ}}_x^2}-\frac{{(y-x_0)}^2}{2{\mathrm{\σ}}_y^2}]}{2\mathrm{\π}{\mathrm{\σ}}_x{\mathrm{\σ}}_y},---\left(4\right)$

Wherein, x ₀, y ₀for bundle spot center; S is mass stopping power;

(5) the flushing-free checking film utilizing Film scanner to scan label orientation and cut, obtains film red channel average pixel value

(6) flushing-free is verified that film perpendicular fasciculus flow path direction such as to be placed at the center, arrange suitable reference ionization chamber counting (MU), the Gaussian bundle spot utilizing step (2) to obtain irradiates; After film fully exposes 24h, scanner is again utilized to obtain film red channel pixel value distribution PV _irr(x, y); Utilize formula (5) to obtain and irradiate the clean optical density distribution of rear film;

$\mathrm{netOD}(x,y)={\mathrm{OD}}_{\mathrm{irr}}(x,y)-{\mathrm{OD}}_{\mathrm{unirr}}(x,y)={\log }_{10}\left(\frac{{\stackrel{\‾}{\mathrm{PV}}}_{\mathrm{unirr}}-{\mathrm{PV}}_{\mathrm{bckg}}}{{\mathrm{PV}}_{\mathrm{irr}}(x,y)-{\mathrm{PV}}_{\mathrm{bckg}}}\right),---\left(5\right)$

Wherein, netOD, OD _irrand OD _unirrbe respectively clean optical density, optical density and pre-irradiation optical density after film irradiates; PV _bckgfor opaque black plastic plate red channel pixel value; Utilize two-dimensional Gaussian function to carry out matching to the clean optical density distribution of two dimension, obtain the central point (x of the clean optical density distribution of film ₀, y ₀), thus obtain netOD (x, y, x ₀, y ₀) distribution function;

(7) corresponding physical dosage D (x, y, x is obtained according to formula (4) to MU value set during this film of irradiation ₀, y ₀) distribution function, compare netOD (x, y, x finally by data processing tools ₀, y ₀) and D (x, y, x ₀, y ₀) distribution function obtain flushing-free checking film dose response curve.

4. the method obtaining flushing-free checking film dosimetry response curve fast as claimed in claim 3, characterized by further comprising step:

(8) step (5) is repeated to step (7), select several reference ionization chamber counting varied in size to irradiate several pieces of flushing-frees respectively and verify that films obtain the dose response curve of multiple dosage range, merge these dose response curves to obtain the wider more reliable response curve of dosage range.

5. the method obtaining flushing-free checking film dosimetry response curve fast as claimed in claim 3, is characterized in that described step (3) is:

Utilize two-dimentional ionization chamber matrix, obtain the X of Gauss's pencil beam spot, the relative dosage distribution in Y-direction, recycles multiple Gaussian function fitting, obtains its relative dosage fitting of distribution parameter w _i, σ _xi, σ _yi(i=1 ..., n), wherein, w _ibe the weight of i-th Gaussian function, meet Σ w _i=1; σ _xi, σ _yibe respectively the parameter of i-th gauss of distribution function.

6. the method obtaining flushing-free checking film dosimetry response curve fast as claimed in claim 3, is characterized in that described step (4) is:

Obtain the distribution of bundle spot absolute physical dosage:

Measured by step (1) and step (3) and obtain K (E) value and bundle spot distribution parameter w _i, σ _xi, σ _yi, bundle spot absolute physical dosage distribution D (x, y) when waiting center to irradiate specific reference ionization chamber counting MU can be derived, that is:

$D(x,y;x_0,y_0)=\frac{1.6\×{10}^{-8}\·S\·\mathrm{MU}\·K\left(E\right)}{2\mathrm{\π}}\underset{i}{\mathrm{\Σ}}\frac{w_i}{{\mathrm{\σ}}_{\mathrm{xi}}{\mathrm{\σ}}_{\mathrm{yi}}}\exp [-\frac{{(x-x_0)}^2}{2{\mathrm{\σ}}_{\mathrm{xi}}^2}-\frac{{(y-x_0)}^2}{2{\mathrm{\σ}}_{\mathrm{yi}}^2}],---\left(4\right)$

Wherein, x ₀, y ₀for bundle spot center; S is mass stopping power.

7. the method obtaining flushing-free checking film dosimetry response curve fast as claimed in claim 3, it is characterized in that in described step (6), directly adopting pixel value to change the data processing method of the clean optical density of replacement calculating, then in step (7), obtain the relation curve of pixel value change and dosage as film dosimetry response curve.