阅读说明：本技术 准直器几何结构的剂量测定投影 (Dosimetry projection of collimator geometry ) 是由 T·伊科南 C·博伊兰 A·哈犹 P·希尔图南 J·考皮南 P·科可恩 V·佩塔加 M 于 2020-02-20 设计创作，主要内容包括：一种计算辐射剂量的方法包括准直器几何结构的剂量测定投影。方法包括限定准直设备的三维(3D)几何结构,三维几何结构限定被配置为允许辐射束穿过的孔,将准直设备沿辐射束投影到平面中的二维(2D)几何结构中,基于准直设备的3D几何结构来计算在邻近孔的位置处的准直设备的剂量测定不透明度值,以及基于在平面中所投影的2D几何结构并且使用在邻近孔的位置处的准直设备的剂量测定不透明度值来计算通过准直设备的辐射束的传送。(A method of calculating a radiation dose includes a dosimetry projection of a collimator geometry. The method includes defining a three-dimensional (3D) geometry of a collimating device, the three-dimensional geometry defining an aperture configured to allow a radiation beam to pass through, projecting the collimating device along the radiation beam into a two-dimensional (2D) geometry in a plane, calculating a dosimetry opacity value of the collimating device at a location adjacent to the aperture based on the 3D geometry of the collimating device, and calculating a delivery of the radiation beam through the collimating device based on the projected 2D geometry in the plane and using the dosimetry opacity value of the collimating device at the location adjacent to the aperture.)

1. A method, comprising the steps of:

defining a three-dimensional (3D) geometry of a collimating device, the three-dimensional geometry defining an aperture configured to allow a radiation beam to pass through;

projecting the collimating device along the radiation beam into a two-dimensional (2D) geometry in a plane;

calculating a dosimetry opacity value of the collimating device at a location adjacent to the aperture based on the 3D geometry of the collimating device; and

calculating a transmission of the radiation beam through the collimating device based on the 2D geometry projected in the plane and using the dosimetric opacity values of the collimating device at the location adjacent to the aperture.

2. The method of claim 1, wherein the calculating of dosimetric opacity values comprises: designating a plurality of points of the collimating device at a boundary adjacent the aperture, calculating dosimetry opacity values at the designated plurality of points, and performing interpolation between the designated plurality of points.

3. The method of claim 2, wherein the calculation of dosimetric opacity values at the specified plurality of points comprises: numerical calculation or analytical calculation.

4. The method of claim 1, wherein calculating the transmission of the radiation beam through the collimating device comprises: calculating the shape and flux of the radiation beam exiting the collimating device.

5. The method of claim 4, further comprising the step of: calculating a dose deposition in an object based on the shape and flux of the radiation beam exiting the collimating device.

6. The method of claim 1, wherein the collimating device comprises: multi-leaf collimators (MLC), Stereotactic Radiosurgery (SRS) cones, motorized collimation clamps, or custom molded collimation blocks.

7. The method of claim 6, wherein at least some of the plurality of beam blocking leaves have a curved leaf end profile in side view.

8. The method of claim 1, wherein the aperture of the collimation device has a size and/or shape suitable for stereotactic radiosurgery.

9. A computer product comprising a non-transitory computer-readable medium storing instructions executable by a computer system, the instructions comprising:

defining a three-dimensional (3D) geometry of a collimating device, the three-dimensional geometry defining an aperture configured to allow a radiation beam to pass through;

projecting the collimating device along the radiation beam into a two-dimensional (2D) geometry in a plane;

calculating a dosimetry opacity value of the collimating device at a location adjacent the aperture based on the 3D geometry of the collimating device; and

calculating a transmission of the radiation beam through the collimating device based on the 2D geometry projected in the plane and using the dosimetric opacity values of the collimating device at the location adjacent to the aperture.

10. The computer product of claim 9, wherein the calculation of the dosimetric opacity value comprises: designating a plurality of points of the collimating device at a boundary adjacent the aperture, calculating dosimetry opacity values at the designated plurality of points, and performing interpolation between the designated plurality of points.

11. The computer product of claim 10, wherein calculating dosimetric opacity values at the specified plurality of points comprises: numerical calculation or analytical calculation.

12. The computer product of claim 9, wherein calculating the transmission of the beam of radiation through the collimating device comprises: calculating the shape and flux of the radiation beam exiting the collimating device.

13. The computer product of claim 12, further comprising the step of: calculating a dose deposition in an object based on the shape and flux of the radiation beam exiting the collimating device.

14. A method, comprising the steps of:

providing a collimator defining an aperture configured to allow at least part of an aperture through which a radiation beam passes;

calculating a dosimetry opacity value of the collimator at a location adjacent to the aperture based on a three-dimensional (3D) geometry of the collimator; and

constructing a computational model for calculating radiation transmission through the collimator, wherein the computational model is based on a two-dimensional (2D) geometry of the collimator and the computer model comprises a function of the dosimetric opacity value of the collimator.

15. The method of claim 14, wherein the calculating of dosimetric opacity values comprises: the thickness of the collimator at one of the positions is calculated along a ray from a point at the source and a point on the projection plane, and the thickness calculation is used to dosimetry the opacity value.

16. The method of claim 14, wherein the calculating of dosimetric opacity values comprises: a plurality of positions of the collimator in the radiation beam are determined, and dosimetry opacity values of the collimator at the plurality of positions are calculated.

17. The method of claim 14, wherein the calculating of dosimetric opacity values comprises: a numerical calculation of dosimetric opacity values at said positions of said collimator, and an estimation of dosimetric opacity values between said positions.

18. The method of claim 14, wherein the calculating of dosimetric opacity values comprises: an analytical calculation of a dosimetry opacity value at said position of said collimator and an analytical estimation of a dosimetry opacity value between said positions.

19. The method of claim 14, further comprising: calculating a dose deposit in the subject using the radiation transmission calculated by the calculation model calculation.

20. The method of claim 14, wherein the collimator comprises a multi-leaf collimator (MLC), a Stereotactic Radiosurgery (SRS) cone, motorized collimation clamps, or a custom molded collimation block.

Technical Field

The present application relates generally to radiation methods and apparatus. In particular, various embodiments of methods of dosimetry projection and calculation of dose deposition for collimator geometry of a treatment plan are described.

Background

External beam radiation therapy requires a treatment plan to determine the desired radiation dose to the target and the maximum dose that can be safely absorbed by healthy tissue or organs within the treatment volume near the target. In treatment planning, the deposited dose within the treatment volume is calculated or predicted using a suitable dose calculation algorithm, which may involve tracking the radiation beam from the source to the treatment volume.

To achieve a desired dose distribution in the target, a collimation device is used in the treatment machine to modulate the size, shape and/or intensity of the beam. For example, multi-leaf collimators (MLC) are widely used in radiotherapy machines to support various forms of treatment, including 3D conformal radiation therapy (3D-CRT), Intensity Modulated Radiation Therapy (IMRT), Volume Modulated Arc Therapy (VMAT), Stereotactic Radiosurgery (SRS), and the like. The MLC comprises a plurality of beam blocking leaf pairs which can be moved independently into and out of the radiation beam. In use, a plurality of selected beam blocking leaves are positioned to form an aperture in the radiation beam through which the unblocked beam passes. The shape and size of the aperture in the MLC defines the shaped field at the target in the isocenter plane. In some applications, the aperture in the MLC is configured to be sufficiently small for small field radiotherapy or Stereotactic Radiosurgery (SRS). Alternatively, the SRS cone may be used to perform stereotactic radiosurgery. The SRS cone is a collimating device, typically made of tungsten, with a small conical hole to allow the radiation beam delivered for the focused beam to pass through.

As the radiation beam from the source passes through the MLC, SRS cone, and/or other collimating device, the characteristics of the beam (including the shape or flux of the beam) are modified and therefore need to be determined to provide input to a dose calculation algorithm to calculate or predict the dose deposited in the treatment volume. One conventional method of calculating the shape or flux of a beam exiting a collimating device, such as an MLC, is to project the MLC geometry along the beam line onto a plane, essentially flattening the three-dimensional (3D) MLC geometry into a two-dimensional (2D) opening, where the structural details of the MLC blade tip are not taken into account in the calculation. While this approach works well in many cases, it becomes less accurate in planning small field radiotherapy, including stereotactic radiotherapy, where the size of the treatment field is comparable to the size of the 3D structural features of the MLC leaf apex. In small field radiotherapy, the 3D geometry details of the MLC must be considered to accurately predict the dose distribution for a small field. However, full 3D models for beam tracking or flux computation are currently too expensive and too slow computationally to be used in a treatment planning system in a clinical setting.

Accordingly, there is a need for beam tracking and dose calculation methods that can provide both accuracy and speed for treatment planning of radiation therapy. There is a particular need for such a method for planning small field radiotherapy using a radiation system comprising a multi-leaf collimator.

Disclosure of Invention

Embodiments of the present disclosure provide a method for tracking or calculating beam flux through a collimating device. The three-dimensional (3D) shape of the collimation device, such as the MLC, is taken into account by local dosimetry projection of the geometry. For example, the dimensions of the MLC portion are projected along the beam into a dosimetry opacity value or dosimetry thickness. The dosimetry projections are based on the true 3D geometry of the MLC, but by localizing the dosimetry projections (e.g., around MLC tips and edges) and by defining boundary points or surfaces, the algorithm can be made faster than a full 3D model. Dosimetric opacity can be calculated by, for example, ray tracing or analysis, and by interpolating between geometric boundaries or using analytical approximations to calculate dosimetric opacity at geometric boundaries. For example, dependencies on variables such as collimator shape and position may be taken into account by parameterizing the dosimetry projections as a function of the variables or by analyzing approximations. The opacity value or thickness of the dosimetry projection can then be used as input to a dose calculation algorithm within the flux calculation module. The method of the present disclosure requires comparable computational effort to current 2D methods, but does significantly improve the accuracy of dose calculation to a level comparable to full 3D models.

In one embodiment, a method comprises the steps of: defining a three-dimensional, 3D, geometry of a collimating device, the 3D geometry defining an aperture configured to allow a radiation beam to pass through, projecting the collimating device into a 2D geometry in a plane along the radiation beam, calculating a dosimetric opacity value of the collimating device at a location adjacent to the aperture based on the 3D geometry of the collimating device, and calculating a transmission of the radiation beam through the collimating device based on the projected 2D geometry in the plane and using the dosimetric opacity value of the collimating device at the location adjacent to the aperture.

In another embodiment, a computer product includes a non-transitory computer-readable medium storing instructions executable by a computer system, the instructions comprising: defining a 3D geometry of a collimating device, the 3D geometry defining an aperture configured to allow a radiation beam to pass through, projecting the collimating device along the radiation beam into a 2D geometry in a plane, calculating a dosimetric opacity value of the collimating device at a location adjacent to the aperture based on the 3D geometry of the collimating device, and calculating a transmission of the radiation beam through the collimating device based on the projected 2D geometry in the plane and using the dosimetric opacity value of the collimating device at the location adjacent to the aperture.

In yet another embodiment, a computer system includes a processor and a memory storing instructions executable by the processor. The instructions include: defining a 3D geometry of a collimating device, the 3D geometry defining an aperture configured to allow a radiation beam to pass through; projecting a collimating device along a radiation beam into a 2D geometry in a plane; calculating a dosimetry opacity value of the collimating device at a position adjacent to the aperture based on the 3D geometry of the collimating device, and calculating a transmission of the radiation beam through the collimating device based on the projected 2D geometry in the plane and using the dosimetry opacity value of the collimating device at the position adjacent to the aperture. .

This summary is provided to introduce a selection of aspects and embodiments of the disclosure in a simplified form and is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The aspects and embodiments selected are presented to provide the reader with a brief summary of certain forms the disclosure may take and are not intended to limit the scope of the disclosure. Other aspects and embodiments of the disclosure are described in the detailed description section.

Drawings

These and various other features and advantages of the present disclosure will be better understood from the following detailed description, taken in conjunction with the drawings provided below and the appended claims, in which:

fig. 1 is a simplified illustration of a radiation system according to an embodiment of the present disclosure.

Fig. 1A is an enlarged perspective view of a multi-leaf collimator (MLC) shown in fig. 1.

Fig. 2 illustrates a three-dimensional (3D) model for computing beam transmission through an MLC.

Fig. 3 illustrates a two-dimensional (2D) model for calculating beam flux through an MLC.

Fig. 4 and 5 illustrate a dosimetry projection model for calculating beam flux through an MLC according to an embodiment of the disclosure.

Fig. 6 is a flow diagram illustrating a method of calculating dose deposition using dosimetric projections of collimator geometry according to an embodiment of the disclosure.

Fig. 7 illustrates an example method of calculation of dosimetric opacity values for MLC leaves, according to an embodiment of the disclosure.

Fig. 8 is a flowchart illustrating example steps of collimator geometry dosimetry projection according to an embodiment of the disclosure.

Fig. 9 is an image showing the results of a dosimetry projection of an example collimator according to an embodiment of the present disclosure.

Fig. 10 shows a statistical graph comparing the accuracy of dose calculations based on various models.

Fig. 11 is a simplified illustration of a computing system according to an embodiment of the disclosure.

Detailed Description

With reference to fig. 1 to 11, various embodiments of a dosimetry projection and dose calculation method of a collimator geometry are described.

Fig. 1 is a simplified illustration of a radiation system 100 in which the methods of the present disclosure may be implemented. As shown, the radiation system 100 may include a radiation source 102 that generates or emits a beam 104 of radiation, such as photons, electrons, protons, or other types of radiation. For example, the radiation source 102 may include a metal target configured to generate an x-ray beam or a photon beam when electrons impinge. It should be noted that although described in connection with various embodiments of an x-ray system, the principles of dosimetry projection of collimator geometry and the method of dose calculation described in the present disclosure may also be implemented in other types of radiation systems, such as ion, electron, carbon or proton systems.

The radiation system 100 can include various collimators or assemblies configured to modify the size, shape, flux, and other characteristics of the beam. By way of non-limiting example, primary collimator 106, which is adjacent to source 102, generally limits the extent to which beam 104 propagates from source 102 toward an object, such as patient 108. Optionally, an electrically driven sub-collimator or collimating clamp 109 may be included to define the field size. A multi-leaf collimator (MLC)110 may be disposed between the source 102 and the patient 108 to shape the beam, as indicated by the shaped field 112 shown in fig. 1A. Placing the MLC 110 in various orientations, the MLC 110 may be rotated about a central beam line or axis 114. Radiation system 100 can optionally include a flattening filter 116 to provide a uniform beam profile. Alternatively, the radiation system does not include any flattening filters or is a flattening-free filter (FFF) to increase the dose rate for treatment. The ion chamber 118 monitors parameters of the beam from the source 102.

The source 102, primary collimator 106, secondary collimator 109, MLC 110 and other devices or components may be enclosed in a treatment head 120, and the treatment head 120 may be rotated about an axis (such as a horizontal axis) by a gantry (not shown). Thus, the system 100 may deliver radiation to a target in the subject 108 from various beam angles. The shape, size, and/or intensity of the beam 104 may be adjusted or dynamically adjusted by the MLC 110 as the beam angle steps or sweeps around the target. The operation of the source 102, MLC 110 and other devices of the radiation system 100 can be controlled by the control system 122. Control system 122 may include a computer processor that receives and executes a treatment plan generated by treatment planning system 1100, which will be described in more detail below.

As shown in fig. 1 and 1A, the MLC 110 may be a single-level MLC or a multi-level MLC. As used herein, the term "MLC" or "multi-leaf collimator" refers to a set of multiple beam blocking leaves 111, each of which can move longitudinally in and out of the beam to modify one or more parameters of the beam (such as beam shape, size, energy, or flux, etc.). Each beam blocking leaf 111 may be driven by a motor with a lead screw or other suitable means. The beam blocking leaves 111 may be arranged in pairs. The beam blocking leaves of each pair may be contacted or telescoped with each other to close or open the path for the radiation beam to pass through the MLC. The bundle blocking leaves may be arranged in opposing rows and supported by a frame, box, bracket, or other support structure having features that allow the individual bundle blocking leaves to extend to and telescope from the bundle. In addition to individual leaf movement, the frame, box, carriage or other support structure may be further moved or translated.

The beam-blocking leaves 111 may have various tip profiles or end configurations, as well as leaf edge profiles or leaf side configurations. By way of non-limiting example, the beam blocking leaves 111 of the MLC 110 may have a flattened front end surface and a flattened side surface. The beam blocking leaves with flattened front end surfaces can be shown to have a straight line orthogonal to the leaf longitudinal movement direction and two right angles on each side of the straight line, both in side and top views. As used herein, the term "top view" refers to a view from a source or viewed along a direction in the central beam line. In some embodiments, the beam-blocking leaves of the MLC 110 may have curved front end surfaces. In a side view, a beam blocking lobe with a curved front end surface may be shown as a curve with a radius and two parallel lines on either side of the curve. In top view, a leaf with a curved front end surface may be shown as having a straight line orthogonal to the longitudinal direction of movement of the leaf and two right angles on each side of the straight line. In the detailed description and the appended claims, the term "square" may be used to describe a tip profile having, in plan view, a straight line orthogonal to the direction of longitudinal movement of the blade and two right angles on each side of the straight line. The term "non-square" may be used to describe any tip profile that does not have a square shape in top view. The non-square shape in top view may include a curved or oval or chamfered leaf shape, as will be described in more detail below.

In some embodiments, the MLC tip may have a circular or non-circular profile. In some embodiments, the MLC leaf side may have tongue and groove engagement (tongue-and-groove) features, a sloped surface, or some other type of profile.

In some embodiments, the beam blocking leaves 111 of the MLC 110 may have a tip profile that includes a combination of curved surface portions and beveled or planar portions on each side of the curved surface portions. The term "chamfered leaf" may be used herein to refer to a leaf that includes a combination of a curved end surface portion and a beveled or planar end surface portion at either side of the curved end surface portion. In a top view or beam perspective view, the end portions or tips of the chamfered leaves may be shown as having a straight midline cross-section orthogonal to the direction of longitudinal leaf movement and a chamfer or angled line cross-section at each side of the straight midline cross-section.

In some embodiments, the MLC 110 may be a multi-level MLC. For example, the MLCs 110 may include a first MLC located in a first level distal to the source 102 and a second MLC located in a second level proximal to the source 102. The first MLC and the second MLC may be arranged such that directions of movement of the individual beam blocking leaves of the first MLC and the second MLC are generally parallel. Alternatively, the first MLC and the second MLC may be arranged such that the direction of movement of the beam blocking leaves of the first MLC is not parallel, e.g. perpendicular to the direction of movement of the beam blocking leaves of the second MLC. The first MLC and the second MLC may be arranged such that a leaf of the second MLC may be laterally offset from a leaf of the first MLC when viewed in a top view or from a source direction.

In some embodiments of the present disclosure, the MLC may not be present, or combined with other collimation or beam shaping devices, including but not limited to collimation clamps, cones, wedges, and filters.

In operation, the MLC 110 may be configured to form an aperture that defines a shaped field 112 that approximates a target geometry at the isocenter plane. Alternatively, the MLC 110 may be configured to define different shaped fields at different MLC orientations and/or beam angles, and the doses of the multiple fields may be added to establish a desired dose distribution in the target. The radiation may be delivered intermittently or statically, with the MLC leaves in place while moving or while delivering the radiation. Radiation can also be delivered dynamically, with MLC leaves moving or the MLC rotating while the radiation is delivered. In some applications, the aperture of the MLC is formed substantially small for small field radiation treatments, such as Stereotactic Radiosurgery (SRS). By way of non-limiting example, the MLC may be configured to form an aperture defining a field size in the range of 1 to 10 mm or 4 to 5 mm. The 1 to 10 mm may be comparable to the projected dimension of an MLC tip, which may have a curved profile in side view or a non-square profile in top view, as described above.

In a treatment plan for radiation delivery, a deposited dose within the target or treatment volume is calculated or predicted using a suitable dose calculation algorithm. To accurately calculate dose deposition, a number of factors need to be considered, including the composition of the tissue and the characteristics of the radiation beam from the source. As the radiation beam produced by the source is transmitted through various collimating devices, including for example MLCs, it is necessary to determine the characteristics of the beam exiting the MLC and provide it to a dose calculation algorithm for use in calculating or predicting the dose deposited in the target or treatment volume.

Fig. 2 shows a method or model for calculating radiation delivery through a collimation device, such as an MLC. According to the method illustrated in fig. 2, a three-dimensional collimator geometric model is constructed and computer software is created based on the three-dimensional model. The three-dimensional model used to calculate the radiation delivery can be very accurate because the details of the three-dimensional collimator geometry, including the fine features of the area near the aperture, are taken into account in the calculation. However, building a 3D model and computer software based on the 3D model is very time consuming in full detail. Radiation delivery computation based on full 3D models is too slow to be used in treatment planning systems in clinical settings, especially in treatment planning optimization.

Fig. 3 shows another method or model for calculating radiation transmission through a collimation device, such as an MLC. According to the method shown in fig. 3, the 3D collimator geometry is flattened or projected along the beam line into a 2D geometry beam line and computer software based on the 2D geometry is created. The 2D model of the computed radiation transmission is fast and suitable for a variety of clinical cases. However, conventional 2D models for calculating radiation transmission are less accurate, especially around the hole edges, because the fine features of the hole edges are not accurately modeled, which is especially relevant when the hole is small, for example for stereotactic radiosurgery. For example, the actual MLC leaf end portion, which has a curved profile in side view, is shown as having a square shape when the MLC leaf is flattened or projected into a 2D geometry along the beamline. As such, the fine features of the actual MLC tip profile are not considered in conventional 2D modeling, which would affect the attenuation or transmission of the radiation beam. Likewise, the fine features of the chamfered lobes described above are also not taken into account in conventional 2D modeling for calculating radiation transmission. In small field radiotherapy, especially stereotactic radiotherapy, the field size may be comparable to the projected dimension of the MLC leaf tip contour. Therefore, the fine features of the aperture edges must be considered to accurately calculate radiation delivery.

Fig. 4 illustrates a new method or model for calculating radiation transmission through a collimating device 410 according to an embodiment of the present disclosure. According to the disclosed method, the geometry of the collimator 410 is flattened or projected in a plane along the beam line from 3D to 2D, and a computational algorithm is created based on the 2D geometry. When the collimator geometry is flattened from 3D to 2D, the dosimetry opacity value or dosimetry thickness of the collimator section will be calculated based on the actual 3D geometry of the collimator. The dosimetric opacity values or thicknesses can be encoded in a 2D geometry-based computational algorithm, as shown by the shaded area around the hole edges in fig. 4. The calculation algorithm model is 2D, so that the calculation speed is high. Furthermore, since the dosimetry opacity value or thickness is obtained based on the actual 3D shape of the collimator, the calculation of the radiation delivery, including the calculation of the aperture edge, is as accurate or nearly as accurate as the 3D model.

Fig. 5 shows that the dosimetry opacity value or thickness depends on the 3D shape of the collimator section (e.g. MLC tip profile) and the position of the collimator distribution in the radiation field. For example, the beam blocking leaves 412 of the MLC 410 at the position shown in fig. 5 exhibit a wider range of shading than the same leaves 412 at a different position shown in fig. 4. This can be interpreted as the dosimetry opacity value or thickness being a function of the length or dimension of the collimator section along the beam path. For convenience in describing various embodiments, the term "dosimetry projection" may be used hereinafter to refer to a method of obtaining a dosimetry opacity value or thickness of a collimator based on its three-dimensional shape or geometry.

Fig. 6 illustrates a dose calculation method using dosimetry projections of collimator geometry according to an embodiment of the disclosure. The method may be implemented in planning radiation delivery using 100 of fig. 1 or other suitable radiation therapy machine. The method may be performed in a treatment planning system 1100 shown in FIG. 11, which is described in more detail below. The method may begin at block 602 by defining a radiation source characteristic. Radiation source characteristics can be defined using a variety of methods, including Monte Carlo simulations and empirical measurements. These methods are well known in the art and thus a detailed description thereof is omitted herein to focus on the description of the various embodiments of the present disclosure. In general, based on the design of the irradiator, which includes the target and the electron beam energy, the flux and energy of the radiation produced by the source and direction at all points on the reference plane can be calculated. The characteristics of the radiation source may be provided as an initial spatial photon spectrum describing flux, energy and direction in a beam reference plane.

At block 604, the geometry of the collimator is defined. As used herein, the term "collimator" refers to any collimation device configured to modify one or more characteristics of radiation from a source, including, but not limited to, multi-leaf collimation devices (MLC), Stereotactic Radiosurgery (SRS) cones, motorized collimation clamps, custom molded or machined collimation blocks, and any other collimation device that may be included in a radiation machine. As used herein, the term "geometry of the collimator" refers to a geometry comprising a contour defining an aperture of the collimator that allows radiation to pass through. The collimator geometry defining the aperture has a three-dimensional configuration in which the cross-sectional shape along the beam-line traversal dimension may or may not vary. The 3D geometry of the collimator may be predetermined by the design of the collimator (such as in the case of custom molded collimator blocks), which in turn may be determined by the geometry of the object to be processed. In the case of a multi-leaf collimator, the 3D geometry of the MLC can be determined by the positioning of a set of beam blocking leaves, which can change over time depending on the treatment plan. As described above, the beam-blocking leaves of an MLC may have a variety of tip profiles, such as curved or rounded leaf end surfaces, the view angle view of the beam or the beam-blocking effect of which may vary depending on the position of the beam-blocking leaves. Furthermore, since the MLC may be rotated around the central beam line, the same geometry of the MLC may have different collimation or attenuation effects when the MLC is in different orientations, especially at the edges of the aperture, as the tips of the beam blocking leaves defining the aperture change the angle relative to the source. The 3D geometry of the MLC can be defined by specifying the spatial position of the beam blocking leaves and their angle relative to the central beam line, the physical dimensions, and the tip profile of the beam blocking leaves, among other variables.

At block 606, dosimetry projections of the collimator are calculated. The dosimetry projection of the collimator comprises a projection of the collimator geometry from 3D to 2D along the beam line, wherein the collimator is represented or coded with dosimetry opacity values along the dimensions of the beam line. As used herein, the term "dosimetric opacity" refers to the quality of a collimator in attenuating radiation. The value of dosimetric opacity is obtained by applying a dosimetric projection method on a given collimator. The value of dosimetric opacity depends on the material of the collimator, the physical dimensions of the collimator or the "thickness" of the material through which the radiation passes, and the position of the collimator relative to the beam centerline. Thus, the term "dosimetric opacity" may be used interchangeably with the term "dosimetric thickness". The dosimetric opacity values of a given collimator section can be calculated using a suitable method based on the real 3D geometry of the collimator.

According to an embodiment of the present disclosure, a local dosimetry projection of the collimator geometry is performed. In the partial dosimetry projection, dosimetry opacity values at positions adjacent to the aperture defined by the collimator are calculated. By way of non-limiting example, a plurality of points or surfaces on the end portion of an MLC leaf are specified, which together represent the boundary of the MLC leaf end or indicate the tip profile. The dosimetric opacity values at these boundary points or surfaces may be calculated by, for example, ray tracing or any other suitable analytical method. Interpolation or analytical approximation may be performed between the boundary points and the surface dosimetric opacity values.

FIG. 7 illustrates an example collimator section (MLC beam stop sheet) and method of calculating a dosimetry opacity value according to an embodiment of the disclosure. In fig. 7, the horizontal axis indicates the leaf projection position and the vertical axis represents the normalized leaf thickness. The curve 702 depicts the physical geometry or true contour of the collimator section at a position relative to the source. As shown, the example MLC leaves have a curved tip profile. The points on the curve 702 may represent designated boundary points or surfaces for calculating a dosimetry opacity value. Curve 704 shows the calculated thickness of the collimator section. As shown, curve 704 substantially overlays curve 702, indicating that the thickness of the collimator section may be accurately calculated using analytical or numerical methods (such as ray tracing and interpolation as known in the art). Based on the results of the ray tracing, the dosimetry projection thickness may be defined, for example, as a function of the approximated ray tracing curve 704. As illustrated in fig. 4 and 5, the dosimetry projection may be defined in such a way that an approximation remains valid and that the dependency of the dosimetry thickness on the MLC leaf positions is taken into account. In fig. 7, the dosimetry projection shape or thickness is indicated by curve 706.

FIG. 8 is a flowchart illustrating example steps for computing collimator dosimetry projections. At 802, the collimator thickness along the ray from point A at the source to point B on the projection plane is calculated. The calculation of the thickness of the collimator can be carried out numerically, for example by ray tracing or analytically. Analytical calculations can be performed in which the collimator is represented by a suitable set of geometric primitives, e.g. two-dimensional circles and lines or three-dimensional cylinders and planes. The collimator position may be fixed when calculating the collimator thickness at 802.

At 804, the calculation of 802 is repeated for a different point B' on the projection plane. The different points B' may be located near the aperture defined by the collimator.

At 806, the calculations of 804 are repeated for different positions of the collimator.

At 808, a thickness function is constructed from the results of 806. This may be accomplished by, for example, interpolating between the points calculated at 806 or by analyzing the approximation. The interpolation-based function may take the form of a pre-computed look-up table coupled with an interpolation algorithm (such as multi-linear interpolation) or other suitable method known in the art. A function based on the analytical approximation may be obtained by numerically fitting an analytical function (such as a multidimensional polynomial) to the points calculated at 806. If an accurate analytical solution is available, an analytical approximation is obtained from the accurate analytical solution by approximating the solution for higher numerical efficiency using numerical calculation methods known in the art.

At 810, the thickness function is converted to dosimetric opacity. Radiation source characteristics such as the dominant particle type and energy spectrum and the radiation delivery physics may be considered in obtaining opacity. This step may depend on the implementation — if the geometry data (thickness) is used for the radiation delivery algorithm instead of the transmission/opacity for the collimator assembly, it can be considered as part of the radiation delivery calculation (608 in fig. 6).

FIG. 9 is an image showing dosimetry projection results, dosimetry opacity using a single MLC leaf as an example. In fig. 9, the vertical axis indicates dosimetric opacity values and the horizontal axis indicates tip position and distance from the tip, respectively. For convenience of explanation, the unit of the axis in fig. 9 is arbitrary. Fig. 9 shows that dosimetric opacity can be represented by a function of two variables, namely leaf position and distance to leaf tip, for an exemplary MLC leaf.

Returning to FIG. 6, at block 608, the method may continue to calculate radiation delivery using the dosimetric opacity value or thickness. Various algorithms have been developed to calculate the transmission of the beam through the collimating device. These methods are well known in the art, and thus their detailed description is omitted to avoid obscuring the description of the various embodiments of the present disclosure. In general, according to embodiments of the present disclosure, an algorithm for calculating radiation delivery takes into account factors including primary sources, extra-focal sources, electronic contamination, photon scattering, etc., and the dosimetric opacity values obtained by the above-described local dosimetry projections are used as inputs to a 2D geometric model-based algorithm to calculate radiation delivery. The beam exiting the collimator may be provided as a spatial flux spectrum in a reference plane.

At block 610, the method may continue with calculating dose deposits in the target within the treatment volume using treatment planning software including a dose calculation algorithm. As a non-limiting example, methods and algorithms based on pencil-bundle convolution superposition may be used. Other suitable methods and algorithms, for example based on Boltzmann Transport Equation (BTE), may also be used. It should be noted that the present disclosure is not limited to a particular dose calculation algorithm. Examples of commercial dose calculation software includeAn XB dose calculation algorithm and an Anisotropy Analysis Algorithm (AAA), both of which are available from warian medical systems, inc. As input for dose calculation, the spatial flux spectrum, or thickness at the boundary of the collimator defining the aperture, which has been calculated using the dosimetric opacity values in block 608, is provided to the dose calculation algorithm.

Embodiments of the present disclosure provide an improved method of calculating radiation transmission or transmission through a collimator using a 2D or quasi-2D model to achieve computational accuracy approximating a 3D model. However, the disclosed method does not require calculation of radiation transmission in a three-dimensional geometry each time a result is required or over the entire spatial extent of the collimator. Instead, the disclosed method may use the above-described dosimetry projections to pre-calculate radiation transmission only once in a 3D or near 3D geometry, or only locally around the aperture defined by the collimator and pre-calculated for different collimator positions (field sizes). Using pre-computed values, 2D or quasi-2D geometries or computational models, algorithms, functions, etc. representing the delivery of radiation in a 3D geometry can be constructed by approximating the 3D details with dosimetric opacity. The 2D or quasi-2D model of dosimetric opacity can be implemented in a flux calculation module of the treatment planning software that calculates dose deposition.

Figure 10 provides a comparison of the accuracy of dose calculation using different methods. The curve shown in FIG. 10The line graph depicts the dose distribution for a small field (e.g., 5x 5 mm). Diagrams 1002 and 1004 illustrate utilizingTreatment planning software andthe XB dose deposition algorithm calculated dose distribution, plot 1002 calculated using conventional 2D MLC modeling, and plot 1004 calculated using a dosimetry projection method according to an embodiment of the disclosure. For comparison, graph 1006 shows the dose distribution calculated using Geant4 monte carlo modeled using a full 3D MLC. The results show that dose deposition is more accurately calculated using the dosimetry projection method described herein (graph 1004), especially at the field edges (at +5 or-5 mm), compared to the conventional 2D MLC modeling method (graph 1002), compared to the reference graph 806.

Various embodiments of dosimetry projection and dose calculation methods for collimator geometries are described in connection with fig. 1-10. It will be appreciated that more or fewer steps, actions, or processes may be incorporated into the methods without departing from the scope of the present disclosure. The arrangement of blocks shown and described herein does not imply a particular order. It will also be appreciated that the method described in connection with fig. 1. Fig. 1-10 may be embodied in a computer-based treatment planning system that performs dosimetry projection and dose calculation methods according to the present disclosure. The present disclosure may be in the form of a computer product comprising a computer-readable medium storing or carrying instructions that, when executed by a computer processor, cause the computer processor to perform the methods described in the present disclosure. The instructions may be implemented as software code executed using a processor used in any suitable computer language, such as Java, C + + or Perl, for example conventional or object-oriented techniques. The computer-readable medium may include any suitable medium that can store or encode a sequence of instructions for execution by a computer processor and that cause the computer processor to perform any one of the methods of the present disclosure. Accordingly, computer readable media shall include, but are not limited to, solid state memories, optical and magnetic disks. Examples of computer readable media include volatile and nonvolatile, removable and non-removable media for storage of computer readable instructions. By way of non-limiting example, computer-readable media include Random Access Memory (RAM), Read Only Memory (ROM), electrically erasable programmable ROM (eeprom) flash memory or other memory technology, compact disc ROM (CD-ROM), Digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed to retrieve the information. In some embodiments, the instructions or software programs may be encoded and transmitted using carrier wave signals suitable for transmission over wired, optical, and/or wireless networks conforming to various protocols, including the Internet. Thus, a computer readable medium may be created using such program encoded data signals. The computer readable medium encoded with the program code may be packaged with a compatible device or provided separately from other devices, for example, by downloading over the internet. Further, any such computer readable medium may reside on or within a computer product, such as a hard drive, a CD, or an entire computer system.

Fig. 11 schematically illustrates a treatment planning system 1100 upon which an embodiment of the present disclosure may be implemented. The treatment planning system 1100 includes a computer system 1110, the computer system 1110 generally including a processor 1112, a memory 1114, a user interface 1116, and a network interface 1118, each of the processors coupled to a system bus 1120.

Processor 1112 may include a Central Processing Unit (CPU), such as is well known in the artProcessor orProcessors, or Graphics Processing Units (GPUs), such asGPUs, or other types of processing units. The processor 1112 can retrieve and execute computer-executable instructions from the memory 1114, which can cause the processor 1112 to perform any methods and/or steps in accordance with embodiments of the present disclosure described above.

The memory 1114 can include any one or combination of volatile memory elements and non-volatile memory elements. Memory 1114 can include Random Access Memory (RAM) or other dynamic storage devices for storing information and instructions to be executed by processor 1112, as well as for storing temporary variables or other intermediate information during execution of instructions by processor 1112. Memory 1114 may also include a Read Only Memory (ROM) or other static storage device for storing static information and instructions for processor 1112. Memory 1114 may also include data storage devices such as magnetic or optical disks for storing information and instructions. The memory 1114 (e.g., a non-transitory computer readable medium) may include programs (logic) for operating the computer system and for executing an application including dosimetry projection and dose calculation as described above or other treatment planning applications. Further, the memory 1114 may include a database that stores any information that may be selected by a user (such as a radiation oncologist or radiation therapist).

User interface devices 1116 may include components such as a keyboard, pointing device, pen, touch input device, voice input device, etc., through which a user interacts with computer system 1110. Output devices such as a display device, printer, speakers, etc. can also be included in computer system 1110.

Network interface 1118 allows the computer system to communicate with other devices or systems via a communication network 1122, such as the internet or an intranet (e.g., a local area network). The network interface 1118 may include a Wi-Fi interface, an ethernet interface, a bluetooth interface, or other wireless or wired interface. Network interface 1118 allows computer system 1110 to receive and transmit electrical, electromagnetic or optical signals that carry data streams representing various types of information. For example, the network interface 1118 may allow the computer system 1110 to receive a data stream representing a software program for treatment planning via the communication network 1122.

Various embodiments have been described with reference to the accompanying drawings. It should be noted that some of the numbers are not necessarily drawn to scale. The drawings are intended to facilitate the description of particular embodiments only and are not intended to be exhaustive or to limit the scope of the disclosure. Furthermore, in the drawings and description, specific details may be set forth in order to provide a thorough understanding of the present disclosure. It will be apparent to one of ordinary skill in the art that some of these specific details may not be used to practice embodiments of the present disclosure. In other instances, well-known components or process steps may not be shown or described in detail to avoid unnecessarily obscuring embodiments of the disclosure.

Unless otherwise specifically defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. As used in the specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. The term "or" refers to a non-exclusive "or" unless the context clearly dictates otherwise. Furthermore, the terms "first" or "second," etc. may be used to distinguish one element from another when describing various similar elements. It should be noted that the terms "first" and "second" as used herein include two or more references. Moreover, unless the context clearly dictates otherwise, the use of the terms "first" or "second" should not be construed as in any particular order.

Those skilled in the art will appreciate that various other modifications may be made. All such and other variations and modifications are contemplated by the inventors and are within the scope of the present disclosure.