Limiting the Dose Rate of Pencil Beam Scanning

Abstract

Calculate the dose rate of a voxel within a particle beam (e.g., a proton beam) treatment field delivered using pencil beam scanning (PBS), and report a representative dose rate for the PBS treatment field. The calculation takes into account the dose accumulation in a local region or sub-volume (e.g., a voxel) as a function of time.

Description

Background Art

[0001] It is well known to use radiotherapy to treat cancer. Generally, radiotherapy involves directing high-energy proton, photon, ion, or electron radiation into a volume within a treatment target of a target or unhealthy tissue (e.g., a tumor or lesion).

[0002] Radiotherapy using a proton beam has significant advantages over using other types of beams. The depth at which a proton beam reaches tissue depends on the beam energy, and the proton beam releases most of its energy (delivers most of its dose) at that depth. The region of the depth-dose curve where most of the energy is released is called the Bragg peak of the beam.

[0003] Before treating a patient with radiation, a treatment plan for the patient is developed. The plan uses simulations and optimizations that can be based on past experience to define various aspects of radiotherapy. Generally, the purpose of the treatment plan is to deliver sufficient radiation to the unhealthy tissue while minimizing the exposure of surrounding healthy tissue to the radiation.

[0004] A radiotherapy technique is called pencil beam scanning (PBS), also known as beam spot scanning. In PBS, a small and focused pencil beam of ionizing radiation is directed to specific positions (beam spots) within the treatment target as prescribed by the treatment plan. For each energy layer of the treatment field, the prescribed beam spot positions are typically arranged in a fixed (raster) pattern, and the pencil beam is delivered along a fixed scan path within the energy layer. By superimposing several layers with different energies, the Bragg peaks of the pencil beams overlap, so that a prescribed dose is uniformly delivered through each treatment field within the treatment target and reaches the edge of the target at a prescribed dose rate.

[0005] Precisely calculating the number and positions (localization and distribution) of the beam spots is crucial. The aim is to determine the beam spot positions: 1) to conform to the contour of the treatment target to improve the lateral penumbra and to avoid exposing healthy tissue outside the treatment target to radiation beyond that required to treat the unhealthy tissue; and 2) to be uniform within the treatment target to avoid dose variations (dose inhomogeneities) within the treatment target so that the prescribed dose is delivered to all parts of the target.

[0006] Interest in the biological effects of ultra-high dose rate irradiation has grown significantly in the past five years. Since the start of the research, studies have shown that by irradiating at a dose rate of approximately 40 Gray (Gy) per second, significant sparing of normal tissues has been demonstrated with equivalent effective tumor growth delay. The sparing effect, known as the FLASH effect, has led to a large number of radiobiological experiments, most of which have been performed using broad electron beams or broad proton beams (bbFLASH). In these experiments, the dose is delivered in the time domain in the form of pulses, with the entire field delivered simultaneously within each pulse. This dose delivery pattern has two characteristic dose rates. The first is the instantaneous dose rate, which is the dose per pulse divided by the pulse duration. The second is the average dose rate, which is the total dose divided by the entire delivery duration.

[0007] PBS introduces additional considerations for defining the dose rate because, as described above, the dose at each point in the treatment field is the sum of contributions from doses delivered asynchronously to multiple beam spots that are close enough to that point to contribute to the dose at that point. While each beam spot will have an instantaneous dose rate and an average dose rate similar to those discussed above for broad beams, the dose rate at any voxel within the PBS field is more difficult to characterize. Summary of the Invention

[0008] For general pencil beam scanning (PBS) (beam spot scanning) and particularly for PBS FLASH radiotherapy, it is important to consider the scan time. Without considering the scan time, the time interval between beam spots delivering the effective dose to a given location is not taken into account. As a result, the dose rate estimation results for the beam spot array will be the same regardless of the time period required to accumulate the total dose.

[0009] Embodiments according to the present invention provide methods and systems for considering the dose accumulation in a local region or sub-volume (e.g., voxel) as a function of time. More specifically, in an embodiment, a method is disclosed that is used to (i) calculate the dose rate in a voxel within a particle beam (e.g., proton beam) treatment field delivered using PBS (in other words, the dose rate distribution of the PBS treatment field), and (ii) report a representative dose rate of the PBS treatment field.

[0010] The disclosed methods consider the unique spatio-temporal delivery pattern of PBS FLASH radiotherapy. This provides a framework for determining and describing the PBS dose rate in an accurate and consistent manner, which is a necessary requirement for cross-study comparison of FLASH results. These methods can be used in radiotherapy planning and can also be used to advance the research and application of PBS FLASH radiotherapy.

[0011] After reading the following detailed description which is illustrated in the various figures, those skilled in the art will recognize these and other objects and advantages of the embodiments according to the present invention.

[0012] The present invention content is provided to introduce some concepts that will be further described in the following detailed description. The present invention content is not intended to identify the key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] This patent or application file contains at least one color drawing. Copies of this patent or patent application publication with color drawings will be provided by the authority upon request and payment of the necessary fees.

[0014] The drawings which are incorporated in and form a part of this specification and in which like reference numerals describe like elements illustrate embodiments of the present disclosure and, together with the detailed description, are used to explain the principles of the present disclosure. The drawings do not necessarily have to be drawn to scale.

[0015] Figure 1 is a block diagram of an example of a computer system that can implement the embodiments described herein.

[0016] Figure 2A , Figure 2B and Figure 2C illustrate examples of pen beam scanning (PBS) patterns as a function of time in embodiments according to the present invention.

[0017] Figure 3A , Figure 3B , Figure 3C and Figure 3D illustrate examples of dose accumulation and instantaneous dose rate for the positions identified in Figure 2A , Figure 2B , Figure 2C in embodiments according to the present invention, each dose accumulation and instantaneous dose rate as a function of time.

[0018] Figure 4A illustrates an example of a PBS pattern as a function of time in an embodiment according to the present invention.

[0019] Figure 4B and Figure 4C illustrate examples of the dose as a function of time at positions in a treatment field in an embodiment according to the present invention.

[0020] Figure 5A illustrates an example of a dose distribution in an embodiment according to the present invention.

[0021] Figure 5B illustrates an example of a PBS dose rate distribution in an embodiment according to the present invention.

[0022] Figure 5C Illustrates an example of a dose rate - volume histogram in an embodiment according to the present invention.

[0023] Figure 6A Illustrates an axial view of an example of a three - dimensional PBS dose rate distribution in an embodiment according to the present invention.

[0024] Figure 6B Illustrates an example of a histogram of PBS dose rate versus volume for regions at different depths of a treatment field in an embodiment according to the present invention.

[0025] Figure 6C Illustrates an example of PBS dose rate versus depth at the center of a treatment field in an embodiment according to the present invention.

[0026] Figure 7 Is a flowchart of an example of a computer - implemented method that can be used in a radiotherapy plan in an embodiment according to the present invention. Detailed Description

[0027] Reference will now be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Although described in connection with these embodiments, it is to be understood that they are not intended to limit the present disclosure to these embodiments. On the contrary, the present disclosure is intended to cover alternatives, modifications, and equivalents that may be included within the spirit and scope of the present disclosure as defined by the appended claims. Further, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it is to be understood that the present disclosure may be practiced without these specific details. In other instances, well - known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure.

[0028] Certain portions of the following detailed description are presented in terms of processes, logic blocks, processing, and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means by which those skilled in the data processing arts most effectively convey the substance of their work to others skilled in the art. In the present application, a process, logic block, process, etc. is conceived of as a self - consistent sequence of steps or instructions leading to a desired result. These steps are those utilizing physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. For general reasons, it has proven convenient at times to refer to these signals as transactions, bits, values, elements, symbols, characters, samples, pixels, etc.

[0029] However, it should be remembered that all these and similar terms will be associated with appropriate physical quantities and are merely convenient labels applied to these quantities. Unless otherwise specified, as will be apparent from the following discussion, it should be understood that throughout this disclosure, discussions using terms such as "access", "determine", "use", "store", "execute", "associate", etc. refer to the actions and processes of a computer system or similar electronic computing device or processor (e.g., Figure 1 computer system 100). Figure 7 flowchart). The computer system or similar electronic computing device manipulates or transforms data represented as physical (electronic) quantities within a computer system memory, register, or other such information storage, transmission, or display device.

[0030] The following discussion may include terms such as "dose", "dose rate", "energy", etc. Unless otherwise stated, a value is associated with each such term. For example, a dose has a value and can have different values. Unless otherwise stated or apparent from the discussion, for simplicity, the term "dose" may refer to, for example, the value of the dose.

[0031] The following detailed description section presents and discusses according to methods. Although the steps and their ordering are disclosed in the figures (e.g., Figure 7 ) that depict the operations of these methods, these steps and their ordering are merely examples. Embodiments are well suited to performing various other steps or variations of the steps enumerated in the flowcharts of the figures herein in a different order than depicted and described herein.

[0032] The embodiments described herein may be discussed in the general context of computer-executable instructions in some form that reside on a computer-readable storage medium, such as program modules, and are executed by one or more computers or other devices. By way of example and not limitation, computer-readable storage media may include non-transitory computer storage media and communication media. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. In various embodiments, the functionality of program modules may be combined or distributed as needed.

[0033] Computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes but is not limited to random access memory, read-only memory (ROM), electrically erasable programmable ROM (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical or magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed to retrieve that information.

[0034] A communication medium can embody computer-executable instructions, data structures, and program modules, and includes any information delivery medium. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wire connection, and wireless media such as acoustic, radio frequency (RF), infrared, and other wireless media. Any of the foregoing combinations can also be included within the scope of computer-readable media.

[0035] Figure 1 FIG. shows a block diagram of an example of a computer system 100 that can implement the embodiments described herein. In a most basic configuration of system 100, system 100 includes at least one processing unit 102 and a memory 104. This most basic configuration is illustrated by the dashed line 106 in Figure 1 FIG. System 100 can also have additional features and / or functionality. For example, system 100 can also include additional storage devices (removable and / or non-removable), including but not limited to magnetic disks, optical disks, or magnetic tapes. Such additional storage devices are illustrated by the removable storage device 108 and the non-removable storage device 120 in Figure 1 FIG. System 100 can also include (one or more) communication connections 122 that allow the device to communicate with other devices, such as in a networked environment using a logical connection to one or more remote computers.

[0036] System 100 also includes (one or more) input devices 124 such as a keyboard, mouse, pen, voice input device, touch input device, etc. Also included are (one or more) output devices 126 such as a display device, speaker, printer, etc. The display device can be, for example, a cathode ray tube display, a light emitting diode display, or a liquid crystal display.

[0037] In Figure 1 the example of FIG., the memory 104 includes computer-readable instructions, data structures, program modules, etc. associated with a treatment planning system (TPS) 150. However, the treatment planning system 150 can alternatively reside in any of the computer storage media used by system 100, or can be distributed across some combination of computer storage media or can be distributed across some combination of networked computers. The treatment planning system 150 is used to evaluate and generate a final (prescribed) treatment plan. The treatment planning system 150 can also be used to perform the calculations and related operations described below.

[0038] The proposed radiotherapy plan is defined (e.g., using Figure 1The treatment planning system 150) is stored in the computer system memory and accessed from that memory. The proposed radiotherapy plan includes parameter values that may affect the dose and dose rate, as well as other parameters. Parameters that may affect the dose and dose rate include, but are not limited to, the number of irradiations of the volume in the treatment target, the duration of each irradiation (irradiation time), and the dose deposited in each irradiation. The parameters may also include the angle (direction) of the beam directed at the treatment target, and the beam energy for each beam. Other parameters are as described above. The volume of the treatment target may be divided into sub-volumes or voxels, in which case the parameter values may be based on each sub-volume or each voxel (e.g., the value of each sub-volume or the value of each voxel).

[0039] A control system (not shown) implemented using a computer system such as computer system 100 may be used to implement the prescribed radiotherapy plan. The control system may control the parameters of the beam generation system, the nozzle, and the patient support device based on the data it receives and according to the prescribed radiotherapy plan, including parameters such as the energy, intensity, direction, size, and / or shape of the beam.

[0040] During treatment, in an exemplary embodiment, the particle beam enters the nozzle, which includes one or more components that affect (e.g., reduce, modulate) the beam energy to control the dose delivered by the beam and / or control the dose-versus-depth curve of the beam, depending on the type of beam. For example, for a proton beam or an ion beam with a Bragg peak, the nozzle may control the position of the Bragg peak within the treatment target.

[0041] In an embodiment according to the present invention, the nozzle emits particles in a beam spot scan beam (also known as a pencil beam). The nozzle is mounted on a movable gantry such that it can be delivered from different directions (angles) relative to the patient (treatment target) on the patient support device, and the position of the patient support device relative to the beam can also be changed. The target area is irradiated by the beam spot scan beam using raster scanning. The increased flexibility obtained by means of beam spot scanning greatly improves the accuracy of the dose delivered for treatment, maximizing the dose delivered to unhealthy tissue and minimizing damage to healthy tissue.

[0042] The beam may deliver a relatively high dose rate (a relatively high dose in a relatively short period of time). For example, the beam may deliver at least 40 Gy in less than one second and may deliver up to 120 Gy or more per second.

[0043] In radiotherapy techniques such as intensity modulated radiotherapy (IMRT) and intensity modulated particle therapy (IMPT) in which the intensity of a particle beam across a delivery field is constant or modulated, the beam intensity varies across each treatment area (volume within a treatment target) of a patient. Depending on the treatment modality, the degrees of freedom available for intensity modulation include beam shaping (collimation and cross-section), beam weighting (spot scanning), spot spacing (delivery pattern), spot radius (interaction range), scanning speed, beam delivery time, number of energy layers, and angle of incidence (which may be referred to as beam geometry). These degrees of freedom effectively result in an infinite number of potential treatment plans, and thus consistently and effectively generating and evaluating high-quality treatment plans is beyond human capabilities and relies on the use of computer systems, especially considering the time constraints associated with using radiotherapy to treat diseases (e.g., cancer) and the large number of patients who undergo or need to undergo radiotherapy during any given period. For IMPT, steep dose gradients are typically used at target boundaries and field edges to enhance dose conformity.

[0044] Embodiments in accordance with the present invention contribute to improving radiotherapy planning and the treatment itself. Compared to conventional techniques, the treatment plans generated considering the present disclosure are superior for avoiding radiation of healthy tissue by optimizing the balance between the dose rate delivered to unhealthy tissue (e.g., a tumor) and the dose rate delivered to surrounding healthy tissue within the volume of a treatment target. Thus, while treatment planning remains a complex task, it can be improved relative to conventional treatment plans.

[0045] In summary, embodiments in accordance with the present disclosure contribute to generating and implementing a treatment plan that is the most effective and has the least (or most acceptable) side effects (e.g., lower dose rates outside the treated area) relative to other plans. Thus, embodiments in accordance with the present invention can specifically improve the field of radiotherapy planning and radiotherapy treatment generally.

[0046] In addition to radiotherapy techniques such as IMRT and IMPT, embodiments in accordance with the present invention can be used for spatially fractionated radiotherapy, including high-dose spatially fractionated grid radiotherapy, pencil beam radiotherapy, and microbeam radiotherapy.

[0047] Defining the dose rate for pencil beam scanning

[0048] Embodiments in accordance with the present invention provide methods and systems for considering the dose accumulation in a local region or sub-volume (e.g., a voxel) as a function of time. More specifically, in an embodiment, a method is disclosed for (i) calculating the dose rate in a voxel within a particle beam (e.g., a proton beam) treatment field delivered using pencil beam scanning (PBS) (also referred to as spot scanning), and (ii) reporting a representative dose rate for the PBS treatment field. These methods and related operations can useFigure 1 executed by the TPS 150 of

[0049] Embodiments in accordance with the present invention facilitate the development of improved methods that can be used to generate radiotherapy plans for radiotherapy (RT) including FLASH RT. For FLASH RT, dose rates of at least 40 Gy in less than 1 second and up to 120 Gy or more per second can be used.

[0050] The disclosed methods account for the unique spatio-temporal delivery pattern of PBS FLASH radiotherapy. This provides a framework for determining and describing PBS dose rates in an accurate and consistent manner, which is a necessary requirement for cross-study comparison of FLASH results. Thus, these methods can also advance the research and application of PBS FLASH radiotherapy, thereby contributing to improved radiotherapy planning.

[0051] Figure 2A , Figure 2B and Figure 2C illustrate pencil beam scanning patterns as a function of time in embodiments in accordance with the present invention. For simplicity of discussion and illustration, Figures 2A - 2C the examples of Figure 2A consider mono-energetic field delivery (in other words, no energy layer switching). Figure 2B shows the beam spot irradiated within the first 10 milliseconds (ms); Figure 2C shows the beam spot irradiated after 92.5 ms; and Figures 2A - 2C shows the beam spot irradiated after 237.5 ms. The scanning pattern is shown as a dashed line in

[0052] Figure 3A , Figure 3B , Figure 3C and Figure 3D illustrate, in embodiments in accordance with the present invention, the dose accumulation and instantaneous dose rate as a function of time for three selected points (a, b, and c) shown in Figures 2A - 2C .

[0053] Figure 3A and Figure 3C respectively show, for three points of interest identified in Figure 2A ( and ), the cumulative dose and instantaneous dose rate plotted, indicating that the time to accumulate the total dose at a given point is limited to a fraction of the total field delivery time.

[0054] Figure 3B and Figure 3D respectively show example electron broad beam FLASH (bbFLASH) (dashed curves) and PBS (solid lines) deliveries, and also respectively show, for the points in Figure 2A ​ The cumulative dose and instantaneous dose rate as a function of time. These plots provide a comparison of the following two characteristics: the points Characteristics of time-dependent dose accumulation, characteristics of similar points in the electron bbFLASH field delivered in a series of pulses. Figure 3B and Figure 3D show that the dose rate within the beam spot of PBS is similar to the instantaneous dose rate of bbFLASH.

[0055] Figures 2A - 2C and Figures 3A - 3D Examples of show the values of dose accumulation in a local region or sub-volume (e.g., voxel) of the PBS field as a function of time. For PBS planning and treatment and for studying FLASH RT, it is beneficial to consider the dose accumulation time of individual voxels, specifically because the FLASH effect may be related to the average dose rate.

[0056] In an embodiment, generally, the dose rate at each voxel of the PBS radiation field is approximately the quotient of the dose of the voxel and the "effective irradiation time" of the voxel. As used herein, the effective irradiation time of each voxel starts when the cumulative dose at the voxel rises above a first threshold dose value and stops when the cumulative dose at the voxel reaches a second threshold dose value. In one embodiment, the second threshold dose value is the total dose at the voxel minus the first threshold dose value. The above quotient yields the dose rate distribution of the voxel within the PBS treatment field.

[0057] To determine and report a representative dose rate of the PBS treatment field, a metric above a specified dose rate of the dose rate distribution is determined. In one embodiment, a user-selectable parameter p is used to determine the p-th percentile of the dose rate distribution such that the (100 - p)-th percentile of the treatment field is above the specified dose rate. For example, if p is 5, then 95% of the treatment field is above the specified dose rate.

[0058] Now refer to Figure 4A 、 Figure 4B and Figure 4C . Figure 4A Illustrates a PBS pattern as a function of time in an embodiment of the present invention. Figure 4B and Figure 4C are curves of the dose at position (in arbitrary units) as a function of time t in an embodiment of the present invention.

[0059] In Figure 4A , "X" indicates an example of the position within the treatment field. Figure 4A The larger points in indicate the pair of positions A PBS beam spot that contributes a significant dose. Times t0 and t1 indicate the effective irradiation time Position Start and end of: That is, at time t0, a first threshold dose value (as described above) is reached, and at time t1, a second threshold dose value is reached.

[0060] Figure 4B It shows that most of the dose accumulates within a relatively narrow time window (represented by the rectangle in the figure). In Figure 4B the example, most of the dose is delivered between 10.0 ms and 92.5 ms of the PBS field delivery period.

[0061] Figure 4C Expanded Figure 4B the time axis and illustrated the effective irradiation time as well as graphical examples of the first and second dose thresholds for positions in the PBS field. In Figure 4C the example, the first threshold dose value is and the second threshold dose value is where is the total dose delivered to position f within the full-field application time t . The value of

[0062] Continuing to refer to Figures 4A - 4C , consider the two-dimensional (2D) plane near the surface of the PBS field as shown in Figures 2A - 2C . The total dose D delivered to position f within the full-field application time t can be expressed as:

[0063]

[0064] where the corresponding average dose rate or "field" dose rate is calculated as follows:

[0065]

[0066] However, as shown in Figures 3A - 3D , most of the dose accumulation at position only occurs during a portion of the full-field application time t f . As described above, for example, Figure 4B illustrates at position (in Figure 4AThe dose accumulated at X (in ) occurs between 10.0 ms and 92.5 ms of the 250 ms PBS field delivery period. The PBS dose rate as defined herein takes this into account. For this purpose, the effective irradiation time is considered In an embodiment, the times t0 and t1 can be defined according to the dose by the following expressions as follows:

[0067] and

[0068]

[0069] In other words, in one embodiment, when the cumulative dose at position exceeds the first threshold dose value, the effective irradiation time starts at time t0, and when the cumulative dose at position exceeds the second threshold dose value, the effective irradiation time ends at time t1; that is, when the cumulative dose at position is within of the total dose the effective irradiation time ends. Figure 4C shows a graphical example of how to calculate In this embodiment, the PBS dose rate at position is the quotient of and as follows:

[0070]

[0071] In an example of an embodiment according to the present invention, for a matrix of 113×113 points directly below the surface of a five-by-five centimeter (cm) monoenergetic (250 meV) PBS treatment field, Figure 5A is the dose distribution curve, while Figure 5B is the PBS dose rate distribution curve. The 50% isodose line is drawn with a dashed line at the periphery of the field shown in Figure 5A and Figure 5B The scan pattern and beam spot positions are drawn with dashed lines and circles, respectively. In this example, the prescribed dose is 10 Gy.

[0072] Figure 5C shows the dose rate-volume histogram (DRVH) of the region enclosed by the 50% isodose line in Figure 5B where the dose is greater than or equal to 50% of the prescribed dose. As shown by the rectangle in Figure 5C 95% of the points have an effective dose rate exceeding 100 Gy / second.

[0073] InFigures 5A - 5C In the example of Figure 5A and Figure 5B is shown as a color display. Figure 5A The uniform dose distribution in

[0074] The first notable observation is the difference in the dose and PBS dose rate distributions. In the PBS dose rate distribution ( Figure 5B ), two distinct features are evident: the discrete and continuous variations in the dose rate.

[0075] The discrete behavior can be understood as follows. In fact, as Figure 4A shown, the effective irradiation time reflects the time required for the scanning path to pass between the beam spots delivered at times t0 and t1. In Figure 4A , the point of interest needs to include just over three rows of beam spots. However, considering Figure 5B the voxels along the x-axis in , the total number of scan lines can vary between 2 and 4, depending on the relative position of the voxel to the scan line, the beam spot spacing, and the beam spot radius (interaction range). As a result, the effective irradiation time will increase or decrease significantly, thus drastically changing the dose rate. In this case, the discrete nature of the delivery pattern and the beam spot interaction range (imposed by the selected value of the threshold

[0076] Refer to Figure 5C the DRVH in Figure 5B to understand the continuous variation of the PBS dose rate across the field (the gradient along the y-axis in ), consider the transmission path length required to deliver the contributing beam spots as a function of the y-position in the field. In general, the number of scan lines affecting the effective irradiation time will decrease as the position of the beam spot of interest Figure 5B approaches the edge where the beam spot pattern is not connected (the edge opposite the U-turn in the pattern), with a minimum at the corners of the treatment field opposite the start and end of the pattern. Refer to Those points in the upper corners of the treatment field include scan time contributions from more beam spots compared to the contributing few adjacent lines.

[0077] To illustrate the basic characteristics of the PBS dose rate in 3D, the dose rate distribution is calculated for a 250 MeV monoenergetic 10×10 cm 2 proton field in a water phantom with a beam spot sigma in air of approximately 3.3 mm, which delivers 10 Gy to an isodepth point located at 10 cm depth. For simplicity but without loss of generality, quasi-static beam spot delivery is assumed, where the dose is deposited at points on a 5 mm square grid, assuming a beam spot delivery time of 2 ms and a scan speed of 10 mm per second. These parameters nominally represent modern scanning systems. Based on these values, for a total field delivery time of 1000 ms, the total dose delivery plus beam traversal time is 2.5 ms per beam spot, and the dose rate is 10 Gy per second.

[0078] For a prescribed dose of 10 Gy, a reasonable threshold of 0.1 Gy is selected. The dose rate distribution is calculated at a grid interval of 2.5 mm in all dimensions.

[0079] The above calculation results are as Figure 6A , Figure 6B and Figure 6C shown. Figure 6A is a color display of an axial view of the 3D PBS dose rate distribution for an example in an embodiment according to the present invention. Figure 6B Illustrates a histogram of PBS dose rate versus volume for regions at different depths of a treatment target that receives at least 50% of the prescribed dose in an embodiment according to the present invention. Figure 6C Illustrates the relationship between PBS dose rate and depth at the center of the treatment field for an example in an embodiment according to the present invention.

[0080] An obvious feature is that the dose rate decreases with depth, which is quantitatively shown in Figure 6C . Since the pencil beam radius (and the influence radius) increases with depth due to multiple Coulomb scattering, the dose rate decreases with increasing depth (up to the Bragg peak) within the irradiated volume. As a result, the beam spot size increases relative to the scan pattern dimension, which leads to an increase in the effective irradiation time with depth, and thus a corresponding decrease in the dose rate. Figure 6B ​The DRVH quantifies the decrease in dose rate with increasing depth. Specifically, in this example, at depths between 0 and 10 cm, 95% of the irradiated volume (defined as the region receiving at least 50% of the prescribed dose) receives greater than 40 Gy per second, while at depths of 0 - 20 cm and 0 - 30 cm, 95% of the irradiated volume receives greater than 36 Gy and greater than 24 Gy per second, respectively.

[0081] The decrease in dose rate with depth can be modulated by selecting a threshold value. Figure 6C Representative depth dose rate (DDR) curves are shown for two values (0.1 Gy and 0.001 Gy). The results show that the dose rate decreases with decreasing threshold value, and approaches the near - field dose rate as the threshold approaches zero. The PBS DDR approaches the value of a single beam spot with increasing threshold value, and approaches the value of a uniform field with decreasing threshold value. The origin for this is similar to 2D discrete features. The sudden change in dose rate for the middle two curves is due to the rapid increase in the effective irradiation time when the beam spot size is increased to include more beam spots contributing to the dose at position .

[0082] In summary, a novel method for calculating the dose rate at each voxel of a scanned pencil beam is disclosed herein, which takes into account the relationship between dose accumulation and irradiation time at that voxel. The method can be applied in 2D and 3D. Although the above discussion is for an example of discrete beam spot delivery, it can be applied to continuous scanning as long as the dose is known, where the beam flux and scanning speed are input parameters. Additionally, this embodiment can be extended to PBS delivery using an extended Bragg peak or any other similar PBS dose delivery.

[0083] As described above, there is a user - selectable parameter: a clock for measuring the effective irradiation time for a voxel is started when a threshold for the cumulative dose is reached. In an embodiment, when the delivered dose is within the total dose at the voxel minus the threshold value, the same threshold is applied for the end - of - irradiation time. In one of the above examples, a value of 0.1 Gy is selected as the threshold or one percent of the prescribed dose of 10 Gy is selected as the threshold. The choice of different thresholds will affect the value of the effective irradiation time and thus the calculated value of the dose rate. Specifically, a decrease in the threshold will result in an effective irradiation time (relative to when the threshold As the time approaches zero, there is an increase in the effective irradiation time of the total field in the limit and a decrease in the calculated dose rate.

[0084] Since there is a distribution in the dose rate calculated for the PBS domain (e.g., see Figure 5B ), it is necessary to meaningfully and concisely characterize the representative PBS dose rate. Such choices include the mean, median, and minimum dose rates in the calculated dose rate distribution. For FLASH RT, since the biological effect only seems to occur above a certain dose rate, it seems reasonable to choose the minimum dose rate. However, this choice may be deviated by outliers. Therefore, in an embodiment according to the present invention, another user-selectable parameter p corresponding to the p-th percentile of the dose rate distribution is used, such that (100 - p) percent of the treatment field is above the corresponding dose rate. In Figure 5C 's example, the 5th percentile is selected such that 95% of the treatment field is above a dose rate of 100 Gy per second.

[0085] For the threshold and the choice of the value of the percentile p affect the reported PBS dose rate. To the extent that the FLASH phenomenon is dose-rate related, there may be implications in terms of associating the reported PBS dose rate with radiobiological observations. For example, choosing the 5th percentile as the representative dose rate means that 5% of the treatment volume does not receive the desired FLASH dose rate. Therefore, in order to further study and understand FLASH, it may be important to standardize the nomenclature for reporting the representative dose rate or the effective dose rate of the PBS treatment field (e.g., proton field). For a given region of interest (e.g., 50% isodose line), the form 's nomenclature is used to indicate that the dose rate is for the threshold and the percentile p in the dose rate distribution selected for the effective dose rate. For Figure 6B 's example, for the irradiated volume between 0 and 10 cm depth, the reported effective dose rate is per second, which means that when the threshold ( ) is 0.1 Gy, 95% of this volume has a dose rate of at least 40 Gy per second.

[0086] Figure 7 is a flowchart 700 of an example of a computer-implemented method in an embodiment according to the present invention. Flowchart 700 can be implemented as computer-executable instructions (e.g., Figure 1 the TPS 150 of Figure 1 ) residing in the memory of a computer system 100 in some form of computer-readable storage medium (e.g.,

[0087] AlthoughFigure 7 The operations in the flowchart are presented as occurring serially and in a specific order, but the present invention is not limited thereto. These operations can be performed in a different order and / or in parallel, and they can also be performed in an iterative manner. As described above, due to the different parameters to be considered, the range of values of these parameters, the interrelationships of these parameters, the treatment plan that needs to be effective but minimize patient risk, the need to quickly generate a high-quality treatment plan, and the need to consistently study the FLASH effect, the use of the TPS 150 that can be reliably executed on the computer system 100 ( Figure 1 ) is important for radiotherapy planning and for studying and understanding the FLASH effect.

[0088] In Figure 7 box 702, the dose value at the voxel in the treatment target is accessed.

[0089] In box 704, the first threshold dose value and the second threshold dose value are accessed or determined. In one embodiment, the second threshold dose value is the difference between the total dose value of the voxel and the first threshold dose value.

[0090] In box 706, the time amount between the time when the dose accumulated at the voxel reaches the first dose value threshold and the time when the dose accumulated at the voxel reaches the second threshold dose value is determined or measured.

[0091] In box 708, using the dose value at the voxel, the first threshold dose value, the second threshold dose value, and the time amount, the dose rate value at the voxel is determined.

[0092] In box 710, the value of the dose rate (from box 708) is stored in the computer system memory as a candidate parameter in the radiotherapy plan.

[0093] In box 712, the dose rate distribution at multiple voxels in the treatment target is determined. The selected value of the dose rate (e.g., an isocontour) is accessed. The measure (e.g., percentile) of the dose rate distribution that exceeds the selected value is determined. The dose rate distribution can be determined as a function of the depth in the treatment target.

[0094] In box 714, the effective dose rate value representing the dose rate distribution is determined and stored in the computer system memory. The measure and the first threshold dose value (from boxes 712 and 704 respectively) are associated with the effective dose rate value in the computer system memory.

[0095] In summary, embodiments according to the present invention generally consider the scan time of PBS (pencil beam scanning), and particularly consider the scan time of PBS FLASH radiotherapy. By considering the scan time, taking into account the time interval between the dose deliveries of the pencil beams, the resulting dose rate estimation for the pencil beam array takes into account the time period required for the cumulative dose.

[0096] Embodiments in accordance with the present invention provide methods and systems for considering dose accumulation in a local region or sub-volume (e.g., voxel) as a function of time. More specifically, in an embodiment, a method is disclosed for (i) calculating the dose rate within a voxel in a particle beam (e.g., proton beam) treatment field delivered using PBS (in other words, the dose rate distribution of the PBS treatment field), and (ii) reporting a representative dose rate of the PBS treatment field.

[0097] The disclosed methods account for the unique spatio-temporal delivery pattern of PBS FLASH radiotherapy. This provides a framework for determining and characterizing the PBS dose rate in an accurate and consistent manner, which is a necessary requirement for cross-study comparison of FLASH results. These methods can be used for radiotherapy planning and also for advancing the research and application of PBS FLASH radiotherapy.

[0098] In summary, embodiments in accordance with the present invention contribute to improving radiotherapy planning and the treatment itself. Compared to conventional techniques, the treatment plans generated as described herein are superior for avoiding radiation of normal tissue by reducing (if not minimizing) the magnitude (and in some cases the overall) of the dose to normal tissue (outside the target) according to the design. When used with FLASH dose rates, the management of patient motion is simplified since the dose is delivered in a short time period (e.g., less than one second).

[0099] In addition to radiotherapy techniques such as IMRT and IMPT where the intensity of the particle beam is constant or modulated across the delivery field, embodiments in accordance with the present invention can be used for spatially fractionated radiotherapy, which includes high-dose spatially fractionated grid radiotherapy, pencil beam radiotherapy, and microbeam radiotherapy. The techniques described herein can be used for stereotactic radiosurgery as well as stereotactic body radiotherapy in the case of single or multiple metastases.

[0100] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the above specific features and acts are disclosed as example forms of implementing the claims.

Claims

1. A computer system, comprising: A processor; And A memory coupled to the processor and including instructions that, when executed, cause the processor to execute a method for planning radiotherapy, the method comprising: Accessing information including dose values at voxels in a treatment target; Accessing information including a first threshold dose value and a second threshold dose value, the second threshold dose value being greater than the first threshold dose value; Determining an amount of time between a time when the cumulative dose at the voxel reaches the first threshold dose value and a time when the cumulative dose at the voxel reaches the second threshold dose value; Using the dose value at the voxel, the first threshold dose value, the second threshold dose value, and the amount of time to determine a dose rate value at the voxel; and Storing the dose rate value as a candidate parameter in a radiotherapy plan.

2. The computer system according to claim 1, wherein the second threshold dose value comprises a difference between a total dose value for the voxel and the first threshold dose value.

3. The computer system according to claim 1, wherein the method further comprises: Determining a dose rate distribution, the dose rate distribution including dose rate values at a plurality of voxels in the treatment target; Accessing information including a selected value of the dose rate; And Determining a measure of the dose rate distribution that exceeds the selected value.

4. The computer system according to claim 3, wherein the method further comprises: Storing, in the memory, an effective dose rate value representing the dose rate distribution.

5. The computer system according to claim 4, wherein storing the effective dose rate value further comprises: Causing, in the memory, the effective dose rate value to be associated with the measure and the first threshold dose value.

6. The computer system according to claim 3, wherein the dose rate distribution is a function of depth in the treatment target.

7. The computer system according to claim 3, wherein the dose rate distribution is determined using parameter values selected from the group consisting of: beam energy; beam delivery mode; interaction range; beam cross-sectional area; beam scanning speed; and beam delivery time.

8. A non-transitory computer-readable storage medium having computer-executable instructions for causing a computer system to execute a method for planning radiotherapy, the method comprising: Accessing information including dose values at voxels in a treatment target; Accessing information including a first threshold dose value and a second threshold dose value, the second threshold dose value being greater than the first threshold dose value; Determining an amount of time between a time when the cumulative dose at the voxel reaches the first threshold dose value and a time when the cumulative dose at the voxel reaches the second threshold dose value; Using the dose value at the voxel, the first threshold dose value, the second threshold dose value, and the amount of time to determine a dose rate value at the voxel; And Storing the dose rate value as a candidate parameter in a radiotherapy plan.

9. The non-transitory computer-readable storage medium according to claim 8, wherein the second threshold dose value comprises a difference between a total dose value for the voxel and the first threshold dose value.

10. The non-transitory computer-readable storage medium according to claim 8, wherein the method further comprises: Determining a dose rate distribution, the dose rate distribution including dose rate values at a plurality of voxels in the treatment target; Accessing information including a selected value of the dose rate; And Determining a measure of the dose rate distribution that exceeds the selected value.

11. The non-transitory computer-readable storage medium according to claim 10, wherein the method further comprises: Storing an effective dose rate value representing the dose rate distribution.

12. The non-transitory computer-readable storage medium according to claim 11, wherein storing the effective dose rate value further comprises: Associating the effective dose rate value with the measure and the first threshold dose value.

13. The non-transitory computer-readable storage medium according to claim 10, wherein the dose rate distribution is a function of depth in the treatment target.

14. The non-transitory computer-readable storage medium according to claim 10, wherein the dose rate distribution is determined using parameter values selected from the group consisting of: beam energy; beam delivery mode; interaction range; beam cross-sectional area; beam scanning speed; and beam delivery time.

15. A computer-implemented method for radiotherapy planning, the method comprising: Accessing information including dose values at voxels in a treatment target; Accessing information including a first threshold dose value and a second threshold dose value, the second threshold dose value being greater than the first threshold dose value; Determining an amount of time between a time when the cumulative dose at the voxel reaches the first threshold dose value and a time when the cumulative dose at the voxel reaches the second threshold dose value; Using the dose value at the voxel, the first threshold dose value, the second threshold dose value, and the amount of time to determine a dose rate value at the voxel; And Storing the dose rate value as a candidate parameter in a radiotherapy plan.

16. The computer-implemented method according to claim 15, wherein the second threshold dose value comprises a difference between a total dose value for the voxel and the first threshold dose value.

17. The computer-implemented method according to claim 15, further comprising: Determining a dose rate distribution, the dose rate distribution including dose rate values at a plurality of voxels in the treatment target; Accessing information including a selected value of the dose rate; And Determining a measure of the dose rate distribution that exceeds the selected value.

18. The computer-implemented method according to claim 17, further comprising storing an effective dose rate value representing the dose rate distribution.

19. The computer-implemented method according to claim 18, wherein storing the effective dose rate value further comprises: Associating the effective dose rate value with the measure and the first threshold dose value.

20. The computer-implemented method according to claim 17, wherein the dose rate distribution is a function of depth in the treatment target.

21. The computer-implemented method according to claim 17, wherein the dose rate distribution is determined using parameter values selected from the group consisting of: beam energy; beam delivery mode; interaction range; beam cross-sectional area; beam scanning speed; and beam delivery time.

Images