Method and device for determining the stopping power for proton therapy

Abstract

A method is provided for determining the stopping power from computed tomography scans. The method includes preparing computed tomography scans of a body region with two different recording energies; determining the stopping power for different CT numbers from dual energy image areas of the computed tomography scans; forming a data field in which the determined values for the stopping power for different CT numbers from dual energy image areas are applied as a function of the CT numbers; forming a look-up table from the data field; determining the stopping power for different CT numbers from single energy image areas of the computed tomography scans by the look-up table. A corresponding device and control device, a corresponding particle therapy system, and a corresponding computed tomography system, are also provided.

Claims

1. A method for determining a stopping power from computed tomography (CT) scans, the method comprising: receiving CT scans of a body region from a CT system having a scanner and an X-ray source, the CT scans comprising a first CT scan having a first recording energy for a first field of view and a second CT scan having a second, different recording energy for a second, different field of view, wherein the first field of view and the second field of view overlap a first part of the body region to provide an overlapping area, wherein the first field of view and the second field of view do not overlap a second part of the body region to provide a non-overlapping area, wherein the non-overlapping area is covered by one field of view of the first or second field of view but not the other field of view, and wherein a dual energy image area is defined by the overlapping area and a single energy image area is defined by the non-overlapping area; determining a dual energy stopping power for different CT numbers from the dual energy image area; forming a data field in which determined values for the determined dual energy stopping power for the different CT numbers from the dual energy image area are applied as a function of the different CT numbers from the dual energy image area; forming a look-up table from the data field; determining a single energy stopping power for different CT numbers from the single energy image area by the look-up table.

2. The method of claim 1, wherein the data field exists as a point cloud and a function which defines values of the look-up table is configured to the point cloud.

3. The method of claim 2, wherein the data field is in a form of a histogram.

4. The method of claim 1, wherein a location-dependent dual energy stopping power and/or single energy stopping power is determined for a number of voxels of a CT scan with known image position.

5. The method of claim 1, wherein different look-up tables are created for different diameters of scanned regions.

6. The method of claim 5, wherein, in the determining of the single energy stopping power for a CT number in the single energy image area, a diameter in the single energy image area is estimated and the single energy stopping power results from a linear interpolation of look-up tables.

7. The method of claim 5, wherein relevant diameters for a look-up table are determined or estimated from a region depicted in an associated CT scan.

8. The method of claim 7, wherein, in the determining of the single energy stopping power for a CT number in the single energy image area, a diameter in the single energy image area is estimated and the single energy stopping power results from a linear interpolation of look-up tables.

9. The method of claim 1, wherein, before the determining of the values of the dual energy stopping power, a beam hardening correction takes place.

10. The method of claim 9, wherein at least one dedicated calibration takes place to generate a dedicated look-up table for the beam hardening correction.

11. The method of claim 1, wherein in a case of the dual energy image area and the single energy image area adjoining in a predetermined transition area with a thickness , an effective stopping power is calculated from the dual energy stopping power of the dual energy image area and the single energy stopping power of the single energy image area and a predetermined transition function w(r) with location parameter r, with 0<r<.

12. The method as claimed in claim 11, wherein the effective stopping power is calculated with the dual energy stopping power, the single energy stopping power, and a transition function w(r) according to the formula:
SPR.sub.Eff(r)=w(r).Math.SPR.sub.DE+(1w(r)).Math.SPR.sub.SE.

13. A device for determining a stopping power from computed tomography (CT) scans, the device comprising: an interface configured to receive CT scans of a body region from a CT system having a scanner and an X-ray source, the CT scans comprising a first CT scan having a first recording energy for a first field of view and a second, different recording energy for a second, different field of view, wherein the first field of view and the second field of view overlap a first part of the body region to provide an overlapping area, wherein the first field of view and the second field of view do not overlap a second part of the body region to provide a non-overlapping area, wherein the non-overlapping area is covered by one field of view of the first or second field of view but not the other field of view, and wherein a dual energy image area is defined by the overlapping area and a single energy image area is defined by the non-overlapping area; and a processor configured to: determine a dual energy stopping power for different CT numbers from the dual energy image area; form a data field in which determined values for the dual energy stopping power for the different CT numbers from the dual energy image area are applied as a function of the CT numbers from the dual energy image area; form a look-up table from the data field; and determine a single energy stopping power for different CT numbers from the single energy image area by the look-up table.

14. A computed tomography or particle therapy system comprising: a scanner; an X-ray source; and a control device configured to: receive computed tomography (CT) scans of a body region from the scanner and the X-ray source, the CT scans comprising a first CT scan having a first recording energy for a first field of view and a second CT scan having a second, different recording energy for a second field of view, wherein the first field of view and the second field of view overlap a first part of the body region to provide an overlapping area, wherein the first field of view and the second field of view do not overlap a second part of the body region to provide a non-overlapping area, wherein the non-overlapping area is covered by one field of view of the first or second field of view but not the other field of view, and wherein a dual energy image area is defined by overlapping areas for the first and second fields of view and a single energy image area is defined by the non-overlapping area; determine a dual energy stopping power for different CT numbers from the dual energy image area; form a data field in which determined values for the dual energy stopping power for the different CT numbers from the dual energy image area are applied as a function of the CT numbers from the dual energy image area; form a look-up table from the data field; and determine a single energy stopping power for different CT numbers from the single energy image area by the look-up table.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is explained again in more detail hereinafter with reference to the attached figures on the basis of exemplary embodiments. In the various figures, the same components have identical reference numerals. The figures are not to scale as a rule. In the diagrams:

(2) FIG. 1 depicts a diagrammatic view of a look-up table according to the prior art.

(3) FIG. 2 depicts an example of a view of a computed tomography scan with two energies and two fields of view FoV.

(4) FIG. 3 depicts an example of an outline of the transition area.

(5) FIG. 4 depicts a diagrammatic block diagram of the method according to an example.

(6) FIG. 5 depicts an example of a data field and a look-up table.

(7) FIG. 6 depicts a diagrammatic view of an imaging system with an exemplary embodiment of a control device for the execution of the method.

(8) FIG. 7 depicts a diagrammatic view of a particle therapy system with an exemplary embodiment of a control device for the execution of the method.

DETAILED DESCRIPTION

(9) FIG. 1 depicts a diagrammatic view of a look-up table L according to the prior art as already explained in the introductory part. Based on calibration measurements, a look-up table L for single energy data is generated. The look-up value curve N assigns each CT value an SPR value at a specific interval.

(10) FIG. 2 depicts a view of a computed tomography scan CA with two recording energies A, B and two fields of view FoV.sub.A, FoV.sub.B. During recording, the two fields of view FoV.sub.A, FoV.sub.B indicated as cones rotate around a determined angular range, (e.g., 180), and in the process, record the body region K, which is shown here as a circle. The field of view FoV.sub.A of the recording energy A scans a larger area of the body region K than the field of view FoV.sub.B of the recording energy B. Image data with both recording energies A, B is present in the inner part of the circle, the dual energy image area AB, and image data with only a single recording energy A is present in the outer part of the circle, the single energy image area (A\B).

(11) FIG. 3 serves to clarify the transition area U. The two circular areas of FIG. 2 corresponding to the dual energy image area AB (inside) and the single energy image area A\B (outside) are shown again here. At the point where these two areas are adjacent, a discontinuity, a jump, would be identifiable in the subsequent data regarding the stopping power SPR.sub.DE and SPR.sub.SE. To compensate for this discontinuity of the data, a transition function w(r) may be employed.

(12) The transition area U is here located inside the dual energy image area AB (edge of the dashed circle to the edge of the white circle) and has a width . If r is a number between 0 and , this transition function w(r) may determine the weighting of the influence of the CT numbers of the dual energy image area AB and the single energy image area A\B on the determined effective stopping power SPR.sub.Eff.

(13) The effective stopping power SPR.sub.Eff may, according to the formula SPR.sub.Eff(r)=w(r).Math.SPR.sub.DE+(1w(r)).Math.SPR.sub.SE, be calculated with the stopping power SPR.sub.DE and SPR.sub.SE and the transition function w(r). For example, w(r)=r may be adopted as a simple transition function w(r) which produces a linear transition, as indicated here. The influence of SPR.sub.DE declines in a linear fashion outwardly and the influence of SPR.sub.SE increases in a linear fashion outwardly.

(14) FIG. 4 depicts a diagrammatic block diagram of the method for determining the stopping power SPR from computed tomography scans CA. The method includes the following acts.

(15) In act I, computed tomography scans CA of a body region K are provided. This may also mean the production of scans. The computed tomography scans CA are produced or provided with two different recording energies A, B. The scans may take place as outlined in FIG. 2.

(16) In act II, which is an optional act, a calculation of CT numbers H from image data BD of the computed tomography scans CA is undertaken. This act may be necessary if the aforementioned computed tomography scans CA are made available to the method in the form of raw data and firstly an image reconstruction takes place, as is explained in more detail, for example, in the context of FIG. 6.

(17) In act III, the stopping power SPR.sub.DE is determined for different CT numbers H from dual energy image areas AB of the computed tomography scans CA, in other words, in those image areas in which image data DB with both recording energies A, B is present.

(18) In act IV, a data field DF is formed in which the determined values for the stopping power SPR.sub.DE for different CT numbers H from dual energy image areas AB are applied as a function of the CT numbers H.

(19) In act V, a look-up table L is formed, for example, in the form of a Hounsfield look-up table (HLUT), from the data field DF. This may be achieved, for example in a data field DF which exists as a point cloud, by adapting (fitting) a function F to the extremes of the point cloud. This function F then determines the values of the look-up table L.

(20) In act VI, the stopping power SPR.sub.SE for different CT numbers H is determined from single energy image areas A\B of the computed tomography scans CA, that is to say, the image areas in which image data SB with a single recording energy A, B is present, from the look-up table L.

(21) FIG. 5 depicts a data field DF produced by the method in which the solid lines are intended to indicate a point cloud of differing intensity. A function F (dashed line), which defines the look-up table L, is fitted into this point cloud.

(22) FIG. 6 depicts a roughly diagrammatic view of a computed tomography system 1 with a control device 10 for the performance of the method. In certain examples, the computed tomography system 1 has a scanner 2 with a gantry in which an X-ray source 3 rotates, which irradiates a patient who is pushed into a measuring area of the gantry by a couch 5 so that the radiation impinges on a respective detector 4 opposite the X-ray source 3.

(23) The computed tomography system 1 is designed to record dual energy scans. It is possible that the X-ray source 3 may generate radiation with two different energies or a second X-ray source (not shown here) with a second detector is present, for example at an angle of 90 to the aforementioned X-ray source 3. Furthermore, it is assumed that the two scans of different recording energy A, B take place with different fields of view FoV.sub.A, FoV.sub.B (see FIG. 2).

(24) It is explicitly pointed out that the exemplary embodiment according to FIG. 6 is only an example of a CT and other CT constructions may be used, for example, with a ring-shaped fixed X-ray detector and/or a plurality of X-ray sources.

(25) Likewise, only the components which are helpful for the description of the disclosure are shown in the control device 10. In principle, such CT systems and associated control devices are known to a person skilled in the art and therefore do not need to be explained in detail.

(26) Here, a core component of the control device 10 is a processor 11 on which various components are implemented in the form of software modules. The components shown in the processor 11 correspond to the components of the device 11.

(27) Furthermore, the control device 10 has a terminal interface 14 to which a terminal 20 is connected, by way of which an operator may operate the control device 10 and thus the computed tomography system 1. A further interface 15 is a network interface for connection to a data bus 21 in order to establish a connection to an Radiology Information System (RIS) or Picture Archiving and Communication System (PACS).

(28) The scanner 2 may be controlled by the control device 10 by way of a control interface 13, e.g., the rotation speed of the gantry, the displacement of the patient couch 5 and the X-ray source 3 itself, for example, are controlled. The raw data RD are read out from the detector 4 via an acquisition interface 12. Moreover, the control device 10 has a storage unit 16 in which, for example, control or measurement protocols may be stored.

(29) An interface 6 for receiving the computed tomography scans CA of a body region K with two different recording energies A, B is embodied on the processor 11 as a software component. In this example, the interface receives raw data RD, which is first prepared. For this purpose, an image data reconstruction unit 18 is implemented in the interface 6 with which the desired image data is reconstructed from the raw data RD obtained via the data acquisition interface 12. This image data reconstruction unit 18 processes the raw data such that the resulting image data corresponds to the CT numbers H or at least contains these.

(30) The reconstructed computed tomography scans CA are forwarded to a first determination unit 7. This determines the stopping power SPR.sub.DE for different CT numbers H from dual energy image areas AB of the computed tomography scans CA.

(31) The determined data is forwarded to a computing unit 8. This forms a data field DF in which the determined values for the stopping power SPR.sub.DE for different CT numbers H from dual energy image areas (AB) are applied as a function of the CT numbers H.

(32) From this data field DF, a look-up table module 9 creates a look-up table L.

(33) Finally, a second determination unit 7a determines the stopping power SPR.sub.SE for different CT numbers H from single energy areas A\B of the computed tomography scans CA from the look-up table.

(34) The determined values for the respective stopping powers SPR.sub.DE and SPR.sub.SE may then be output on the terminal 20, be stored in the storage unit 16 or be made available to other devices by the data bus 21 or stored in a network storage unit.

(35) FIG. 7 depicts a roughly diagrammatic view of a particle therapy system 1a with an exemplary embodiment of a control device 10 for execution of the method. The particle therapy system 1a is here shown as an accelerator system and includes three treatment places 5a. By way of the beamline 1c shown on the right of the figure, pre-accelerated particles, for example protons, are introduced into an accelerator ring 1b, there accelerated to terminal velocity and if necessary, stored. The particles are directed to the treatment places 5a by way of an extraction beamline 1d and are there available for the treatment of patients.

(36) The particle energy is precisely controlled so that the particle energy develop their maximum effect at a clearly defined place in the patient. The stopping power in the corresponding body region K of the patient is an important measurement for the determination of this energy.

(37) The control device 10 in the processor 11 of which the device is formed, as already explained in more detail in FIG. 6, for example controls the energy of the accelerator ring 1b and extraction by way of the extraction beamline 1d. The device in the processor 11 may determine the stopping power in the relevant body region K from appropriate computed tomography scans CA and the control device 10 determine the appropriate accelerator energy from this stopping power and control the accelerator accordingly. It may be advantageous if the stopping power is known as precisely as possible. The more precisely the stopping power may be determined, the more precise the planning, which directly affects the effectiveness of the radiation.

(38) It is finally pointed out again that the method previously described in detail and the computed tomography system 1 shown and the particle therapy system 1a are only exemplary embodiments which may be modified by a person skilled in the art in a variety of ways without departing from the scope of the disclosure. Furthermore, the use of the indefinite article a or an does not exclude the possibility of the relevant features also being present multiple times. Likewise, the terms unit and module do not exclude the relevant components from including a plurality of interacting subcomponents which may, if necessary, also be spatially distributed.

(39) Although the disclosure has been illustrated and described in detail by the exemplary embodiments, the disclosure is not restricted by the disclosed examples and the person skilled in the art may derive other variations from this without departing from the scope of protection of the disclosure. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.

(40) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.