# Patent

## Title
System and method of generating contour structures using a dose volume histogram

## Abstract

A system and method of defining a new region of interest for an existing region of interest using a dose volume histogram. The method includes the acts of generating a dose volume histogram of radiation dose for a pre-existing region of interest, selecting a subset of the dose volume histogram, and defining a new region of interest that corresponds to the selected subset of the dose volume histogram.

## Background
RELATED APPLICATIONS
This application claims priority to U.S. Provisional Patent Application No. 60/701,580, filed on Jul. 22, 2005, titled SYSTEM AND METHOD FOR FEEDBACK GUIDED QUALITY ASSURANCE AND ADAPTATIONS TO RADIATION THERAPY TREATMENT, the entire contents of which are incorporated herein by reference.


BACKGROUND
Over the past decades improvements in computers and networking, radiation therapy treatment planning software, and medical imaging modalities (CT, MRI, US, and PET) have been incorporated into radiation therapy practice. These improvements have led to the development of image guided radiation therapy (“IGRT”). IGRT is radiation therapy that uses cross-sectional images of the patient's internal anatomy to better target the radiation dose in the tumor while reducing the radiation exposure to healthy organs. The radiation dose delivered to the tumor is controlled with intensity modulated radiation therapy (“IMRT”), which involves changing the size, shape, and intensity of the radiation beam to conform to the size, shape, and location of the patient's tumor. IGRT and IMRT lead to improved control of the tumor while simultaneously reducing the potential for acute side effects due to irradiation of healthy tissue surrounding the tumor.
IMRT is becoming the standard of care in several countries. However, in many situations, IMRT is not used to treat a patient due to time, resources, and billing constraints. Daily images of the patient can be used to guarantee that the high gradients generated by IMRT plans are located on the correct position for patient treatment. Also these images can provide necessary information to adapt the plan online or offline if needed.
It is commonly known in the field of radiation therapy that there are many sources of uncertainty and change that can occur during a course of a patient's treatment. Some of these sources represent random errors, such as small differences in a patient's setup position each day. Other sources are attributable to physiological changes, which might occur if a patient's tumor regresses or the patient loses weight during therapy. A third possible category regards motion. Motion can potentially overlap with either of the other categories, as some motion might be more random and unpredictable, such as a patient coughing or passing gas, whereas other motion can be more regular, such as breathing motion, sometimes.
SUMMARY
In radiation therapy, uncertainties can affect the quality of a patient's treatment. For example, when delivering a treatment dose to a target region, it is standard practice to also treat a high-dose “margin” region about the target. This helps ensure that the target receives the desired dose, even if its location changes during the course of the treatment, or even during a single fraction. The less definite a target's location, the larger the margins that typically need to be used.
Adaptive radiation therapy generally refers to the concept of using feedback during the course of radiation therapy treatment to improve future treatments. Feedback can be used in off-line adaptive therapy processes and on-line adaptive therapy processes. Off-line adaptive therapy processes occur while the patient is not being treated, such as in between treatment fractions. In one version of this, during each fraction, a new CT image of the patient is acquired before or after each of the fractions. After the images are acquired from the first few treatment fractions, the images are evaluated to determine an effective envelope of the multi-day locations of target structures. A new plan can then be developed to better reflect the range of motion of the target structure, rather than using canonical assumptions of motion. A more complex version of off-line adaptive therapy is to recalculate the delivered dose after each fraction and accumulate these doses, potentially utilizing deformation techniques, during this accumulation to account for internal motion. The accumulated dose can then be compared to the planned dose, and if any discrepancies are noted, subsequent fractions can be modified to account for the changes.
On-line adaptive therapy processes typically occur while the patient is in the treatment room, and potentially, but not necessarily, during a treatment delivery. For example, some radiation therapy treatment systems are equipped with imaging systems, such as on-line CT or x-ray systems. These systems can be used prior to treatment to validate or adjust the patient's setup for the treatment delivery. The imaging systems may also be used to adapt the treatment during the actual treatment delivery. For example, an imaging system potentially can be used concurrently with treatment to modify the treatment delivery to reflect changes in patient anatomy.
One aspect of the present invention is to disclose new opportunities for the application of adaptive therapy techniques, and additional aspects are to present novel methods for adaptive therapy. In particular, adaptive therapy has typically focused on feedback to modify a patient's treatment, but the present invention focuses on adaptive therapy processes being used in a quality assurance context. This is particularly true in the context of whole-system verification.
For example, a detector can be used to collect information indicating how much treatment beam has passed through the patient, from which the magnitude of the treatment output can be determined as well as any radiation pattern that was used for the delivery. The benefit of this delivery verification process is that it enables the operator to detect errors in the machine delivery, such as an incorrect leaf pattern or machine output.
However, validating that the machine is functioning properly does not itself ensure proper delivery of a treatment plan, as one also needs to validate that the external inputs used to program the machine are effective and consistent. Thus, one aspect of the invention includes the broader concept of an adaptive-type feedback loop for improved quality assurance of the entire treatment process. In this aspect, the invention includes the steps of positioning the patient for treatment and using a method for image-guidance to determine the patient's position, repositioning the patient as necessary for treatment based upon the image-guidance, and beginning treatment. Then, either during or after treatment, recalculating the patient dose and incorporating the patient image information that had been collected before or during treatment. After completion of these steps, quality assurance data is collected to analyze the extent to which the delivery was not only performed as planned, but to validate that the planned delivery is reasonable in the context of the newly available data. In this regard, the concept of feedback is no longer being used to indicate changes to the treatment based on changes in the patient or delivery, but to validate the original delivery itself.
As an example, it is possible that a treatment plan might be developed for a patient, but that the image used for planning became corrupted, such as by applying an incorrect density calibration. In this case, the treatment plan will be based upon incorrect information, and might not deliver the correct dose to the patient. Yet, many quality assurance techniques will not detect this error because they will verify that the machine is operating as instructed, rather than checking whether the instructions to the machine are based on correct input information. Likewise, some adaptive therapy techniques could be applied to this delivery, but if the calibration problem of this example persisted, then the adapted treatments would suffer from similar flaws.
There are a number of processes that can be used to expand the use of feedback for quality assurance purposes. For example, in one embodiment, this process would include the delivery verification techniques described above. The validation of machine performance that these methods provide is a valuable component of a total-system quality assurance toolset. Moreover, the delivery verification processes can be expanded to analyze other system errors, such as deliveries based on images with a truncated field-of-view.
In one embodiment, the invention provides a method of defining a new region of interest using a dose volume histogram. The method comprises the acts of generating a dose volume histogram of radiation dose for a pre-existing region of interest, selecting a subset of the dose volume histogram, and defining a new region of interest that corresponds to the selected subset of the dose volume histogram.
In another embodiment, the invention provides a method comprising the acts of generating a first dose volume representing a first radiation dose for a patient, generating a second dose volume representing a second radiation dose for the patient, comparing the first dose volume and the second dose volume, generating a dose volume histogram based on the comparison, selecting a subset on the dose volume histogram, and generating a region of interest based on the selected subset.
In yet another embodiment, the invention provides a system for generating contours using a dose volume histogram. The system comprises a radiation therapy treatment device and a software program. The radiation therapy treatment device is operable to deliver a treatment plan to a patient and includes a computer processor. The software program is stored in a computer readable medium accessible by the computer processor and is operable to generate a dose volume histogram of radiation dose for a pre-existing region of interest, select a subset of the dose volume histogram, and define a new region of interest that corresponds to the selected subset of the dose volume histogram.
In another embodiment, the invention provides a method of defining a new region of interest using a dose volume histogram. The method comprises the acts of generating a first dose volume, generating a second dose volume, comparing the first dose volume and the second dose volume, generating a histogram based on the comparison, selecting a subset on the histogram, and generating a region of interest based on the selected subset.
In another embodiment, the invention provides a method of defining a new region of interest using a histogram. The method comprises the acts of generating a histogram of radiation dose for a pre-existing region of interest, selecting a subset of the histogram, and defining a new region of interest that corresponds to the selected subset of the histogram.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a radiation therapy treatment system.
FIG. 2 is a perspective view of a multi-leaf collimator that can be used in the radiation therapy treatment system illustrated in FIG. 1.
FIG. 3 is a schematic illustration of the radiation therapy treatment system of FIG. 1.
FIG. 4 is a schematic diagram of a software program used in the radiation therapy treatment system.
FIG. 5 illustrates an image 122 of the head and neck region of a patient 14 including a plurality of identified targets.
FIG. 6 illustrates a dose volume histogram generated by the radiation therapy treatment system of FIG. 1.
FIG. 7 illustrates new contours that were generated based on the dose volume histogram of FIG. 6.
FIG. 8 illustrates which portions of the dose volume histogram of FIG. 6 correspond to the newly-generated contours of FIG. 7.
FIG. 9 is a flow chart of a method of generating a contour using a dose volume histogram according to one embodiment of the present invention.
FIG. 10 is a flow chart of a method of generating a contour using a dose volume histogram according to one embodiment of the present invention.



DETAILED DESCRIPTION
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
Although directional references, such as upper, lower, downward, upward, rearward, bottom, front, rear, etc., may be made herein in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first”, “second”, and “third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance.
In addition, it should be understood that embodiments of the invention include both hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software. As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific mechanical configurations illustrated in the drawings are intended to exemplify embodiments of the invention and that other alternative mechanical configurations are possible.
FIG. 1 illustrates a radiation therapy treatment system 10 that can provide radiation therapy to a patient 14. The radiation therapy treatment can include photon-based radiation therapy, brachytherapy, electron beam therapy, proton, neutron, or particle therapy, or other types of treatment therapy. The radiation therapy treatment system 10 includes a gantry 18. The gantry 18 can support a radiation module 22, which can include a radiation source 24 and a linear accelerator 26 operable to generate a beam 30 of radiation. Though the gantry 18 shown in the drawings is a ring gantry, i.e., it extends through a full 360° arc to create a complete ring or circle, other types of mounting arrangements may also be employed. For example, a C-type, partial ring gantry, or robotic arm could be used. Any other framework capable of positioning the radiation module 22 at various rotational and/or axial positions relative to the patient 14 may also be employed. In addition, the radiation source 24 may travel in path that does not follow the shape of the gantry 18. For example, the radiation source 24 may travel in a non-circular path even though the illustrated gantry 18 is generally circular-shaped.
The radiation module 22 can also include a modulation device 34 operable to modify or modulate the radiation beam 30. The modulation device 34 provides the modulation of the radiation beam 30 and directs the radiation beam 30 toward the patient 14. Specifically, the radiation beam 34 is directed toward a portion of the patient. Broadly speaking, the portion may include the entire body, but is generally smaller than the entire body and can be defined by a two-dimensional area and/or a three-dimensional volume. A portion desired to receive the radiation, which may be referred to as a target 38 or target region, is an example of a region of interest. The target 38 may also include a margin around or partially around the target. Another type of region of interest is a region at risk. If a portion includes a region at risk, the radiation beam is preferably diverted from the region at risk. The patient 14 may have more than one target region that needs to receive radiation therapy. Such modulation is sometimes referred to as intensity modulated radiation therapy (“IMRT”).
The modulation device 34 can include a collimation device 42 as illustrated in FIG. 2. The collimation device 42 includes a set of jaws 46 that define and adjust the size of an aperture 50 through which the radiation beam 30 may pass. The jaws 46 include an upper jaw 54 and a lower jaw 58. The upper jaw 54 and the lower jaw 58 are moveable to adjust the size of the aperture 50.
In one embodiment, and illustrated in FIG. 2, the modulation device 34 can comprise a multi-leaf collimator 62, which includes a plurality of interlaced leaves 66 operable to move from position to position, to provide intensity modulation. It is also noted that the leaves 66 can be moved to a position anywhere between a minimally and maximally-open position. The plurality of interlaced leaves 66 modulate the strength, size, and shape of the radiation beam 30 before the radiation beam 30 reaches the target 38 on the patient 14. Each of the leaves 66 is independently controlled by an actuator 70, such as a motor or an air valve so that the leaf 66 can open and close to permit or block the passage of radiation. The actuators 70 can be controlled by a computer 74 and/or controller.
The radiation therapy treatment system 10 can also include a detector 78, e.g., a kilovoltage or a megavoltage detector, operable to receive the radiation beam 30. The linear accelerator 26 and the detector 78 can also operate as a computed tomography (CT) system to generate CT images of the patient 14. The linear accelerator 26 emits the radiation beam 30 toward the target 38 in the patient 14. The target 38 absorbs some of the radiation. The detector 78 detects or measures the amount of radiation absorbed by the target 38. The detector 78 collects the absorption data from different angles as the linear accelerator 26 rotates around and emits radiation toward the patient 14. The collected absorption data is transmitted to the computer 74 to process the absorption data and to generate images of the patient's body tissues and organs. The images can also illustrate bone, soft tissues, and blood vessels.
The CT images can be acquired with a radiation beam 30 that has a fan-shaped geometry, a multi-slice geometry or a cone-beam geometry. In addition, the CT images can be acquired with the linear accelerator 26 delivering megavoltage energies or kilovoltage energies. It is also noted that the acquired CT images can be registered with previously acquired CT images (from the radiation therapy treatment system 10 or other image acquisition devices, such as other CT scanners, MRI systems, and PET systems). For example, the previously acquired CT images for the patient 14 can include identified targets 38 made through a contouring process. The newly acquired CT images for the patient 14 can be registered with the previously acquired CT images to assist in identifying the targets 38 in the new CT images. The registration process can use rigid or deformable registration tools.
In some embodiments, the radiation therapy treatment system 10 can include an x-ray source and a CT image detector. The x-ray source and the CT image detector operate in a similar manner as the linear accelerator 26 and the detector 78 as described above to acquire image data. The image data is transmitted to the computer 74 where it is processed to generate images of the patient's body tissues and organs.
The radiation therapy treatment system 10 can also include a patient support, such as a couch 82 (illustrated in FIG. 1), which supports the patient 14. The couch 82 moves along at least one axis 84 in the x, y, or z directions. In other embodiments of the invention, the patient support can be a device that is adapted to support any portion of the patient's body. The patient support is not limited to having to support the entire patient's body. The system 10 also can include a drive system 86 operable to manipulate the position of the couch 82. The drive system 86 can be controlled by the computer 74.
The computer 74, illustrated in FIGS. 2 and 3, includes an operating system for running various software programs and/or a communications application. In particular, the computer 74 can include a software program(s) 90 that operates to communicate with the radiation therapy treatment system 10. The software program(s) 90 is operable to receive data from external software programs and hardware and it is noted that data may be input to the software program(s) 90.
The computer 74 can include any suitable input/output device adapted to be accessed by medical personnel. The computer 74 can include typical hardware such as a processor, I/O interfaces, and storage devices or memory. The computer 74 can also include input devices such as a keyboard and a mouse. The computer 74 can further include standard output devices, such as a monitor. In addition, the computer 74 can include peripherals, such as a printer and a scanner.
The computer 74 can be networked with other computers 74 and radiation therapy treatment systems 10. The other computers 74 may include additional and/or different computer programs and software and are not required to be identical to the computer 74, described herein. The computers 74 and radiation therapy treatment system 10 can communicate with a network 94. The computers 74 and radiation therapy treatment systems 10 can also communicate with a database(s) 98 and a server(s) 102. It is noted that the software program(s) 90 could also reside on the server(s) 102.
The network 94 can be built according to any networking technology or topology or combinations of technologies and topologies and can include multiple sub-networks. Connections between the computers and systems shown in FIG. 3 can be made through local area networks (“LANs”), wide area networks (“WANs”), public switched telephone networks (“PSTNs”), wireless networks, Intranets, the Internet, or any other suitable networks. In a hospital or medical care facility, communication between the computers and systems shown in FIG. 3 can be made through the Health Level Seven (“HL7”) protocol or other protocols with any version and/or other required protocol. HL7 is a standard protocol which specifies the implementation of interfaces between two computer applications (sender and receiver) from different vendors for electronic data exchange in health care environments. HL7 can allow health care institutions to exchange key sets of data from different application systems. Specifically, HL7 can define the data to be exchanged, the timing of the interchange, and the communication of errors to the application. The formats are generally generic in nature and can be configured to meet the needs of the applications involved.
Communication between the computers and systems shown in FIG. 3 can also occur through the Digital Imaging and Communications in Medicine (“DICOM”) protocol with any version and/or other required protocol. DICOM is an international communications standard developed by NEMA that defines the format used to transfer medical image-related data between different pieces of medical equipment. DICOM RT refers to the standards that are specific to radiation therapy data.
The two-way arrows in FIG. 3 generally represent two-way communication and information transfer between the network 94 and any one of the computers 74 and the systems 10 shown in FIG. 3. However, for some medical and computerized equipment, only one-way communication and information transfer may be necessary.
FIG. 4 is a schematic illustration of the software program 90. The software program 90 includes a plurality of modules that communicate with one another to perform functions of the radiation therapy treatment process. The various modules communicate with one another to determine if delivery of the radiation therapy treatment plan occurred as intended.
The software program 90 includes a treatment plan module 106 operable to generate a treatment plan for the patient 14 based on data input to the system 10 by medical personnel. The data includes one or more images (e.g., planning images and/or pre-treatment images) of at least a portion of the patient 14. The treatment plan module 106 separates the treatment into a plurality of fractions and determines the radiation dose for each fraction or treatment based on the prescription input by medical personnel. The treatment plan module 106 also determines the radiation dose for the target 38 based on various contours drawn around the target 38. Multiple targets 38 may be present and included in the same treatment plan.
The software program 90 also includes a patient positioning module 110 operable to position and align the patient 14 with respect to the isocenter of the gantry 18 for a particular treatment fraction. While the patient is on the couch 82, the patient positioning module 110 acquires an image of the patient 14 and compares the current position of the patient 14 to the position of the patient in a planning image. If the patient's position needs to be adjusted, the patient positioning module 110 provides instructions to the drive system 86 to move the couch 82 or the patient 14 can be manually moved to the new position. In one construction, the patient positioning module 110 can receive data from lasers positioned in the treatment room to provide patient position data with respect to the isocenter of the gantry 18. Based on the data from the lasers, the patient positioning module 110 provides instructions to the drive system 86, which moves the couch 82 to achieve proper alignment of the patient 14 with respect to the gantry 18. It is noted that devices and systems, other than lasers, can be used to provide data to the patient positioning module 110 to assist in the alignment process.
The software program 90 also includes an image module 114 operable to acquire images of at least a portion of the patient 14. The image module 114 can instruct the on-board image device, such as a CT imaging device to acquire images of the patient 14 before treatment commences, during treatment, and after treatment according to desired protocols. Other off-line imaging devices or systems may be used to acquire pre-treatment images of the patient 14, such as non-quantitative CT, MRI, PET, SPECT, ultrasound, transmission imaging, fluoroscopy, RF-based localization, and the like. The acquired images can be used for registration of the patient 14 and/or to determine or predict a radiation dose to be delivered to the patient 14. The acquired images also can be used to determine a radiation dose that the patient 14 received during the prior treatments.
The software program 90 also includes an analysis module 118 operable to analyze dose distributions during the treatment planning process and/or the post-treatment process. Dose distributions are typically three-dimensional volumes, and can be analyzed with a two-dimensional plot called a dose volume histogram (“DVH”). A DVH can include a plurality of subsets, which may include the dose volume curve and an area above and below the curve. The analysis module 118 can generate the DVH and display it on the screen/monitor for viewing by medical personnel.
FIGS. 5-8 illustrate a sample DVH of the head and neck region of a patient 14. FIG. 5 illustrates an image 122 of the head and neck region of the patient 14 including a plurality of identified targets. FIG. 5 also illustrates a DVH 126 corresponding to some of the identified targets of the head and neck region that received radiation. The DVH 126 includes a curve 130 representing a dose volume of radiation that was delivered to the patient 14. FIG. 6 illustrates an enlarged version of the DVH 126 including a plurality of subsets 134, 138, and 142. Each subset 134, 138, and 142 indicates an amount of radiation delivered to a particular area 146, 150, and 154, respectively of the head. FIG. 7 illustrates new contours that were generated based on the dose distribution of the particular targets 146, 150, and 154 according to the DVH 126. FIG. 8 illustrates which subset 134, 138, and 142 of the DVH 126 corresponds to the newly-generated contours.
A DVH helps provide an understanding of the range of doses provided to each target. This understanding can be useful during the treatment planning process for determining which structures are receiving too much or too little radiation dose. Based on the DVH, the medical personnel can modify the treatment plan to ensure accurate delivery of radiation to the target.
In the course of planning treatment of a patient 14, medical personnel using the system 10 can view the DVH on the display/monitor and select a region of or point on a DVH curve to identify the portions of the 3D image or dose volumes that are receiving doses in the specified range. This method can assist in treatment planning because it can help the user better understand which regions are the most difficult to dose correctly.
In one aspect of the invention, the analysis module 118 can retrospectively analyze dose distributions for radiation treatment plans that have already been delivered to the patient 14. In this aspect, the user can evaluate the success of the treatment by accessing the analysis module 118 to select a region on the DVH plot to identify the locations of dose discrepancy on the dose map. In addition, the analysis module 118 can further utilize not just a single dose distribution and corresponding DVH plot, but effectively compare a plurality of dose volumes, e.g., the planned dose volume with a recalculated dose volume based upon the actual delivery. By incorporating this additional information, the DVH plot can show both dose volumes, or the comparison between dose volumes, and likewise, interaction with the DVH plot can indicate the regions of the dose distribution that are planned to receive a given range of doses and show the regions that the delivered radiation dose varied from the planned radiation doses. A comparison of dose volumes can be a series of sums, or differences, or other appropriate mathematical functions.
As one example, the dose delivered to the patient 14 can be evaluated using a gamma index. The gamma (γ) index is used to simultaneously test both percent dose difference in plateau regions and distance to agreement in high gradient regions. Percent dose difference is a useful metric in regions of uniform dose—the plateau regions—but is not appropriate for high gradient regions. Distance to agreement is a more appropriate metric for high dose gradient regions. The γ index was introduced by Low et. al. (Daniel A. Low, William B. Harms, Sasa Mutic, James A. Purdy, “A technique for the quantitative evaluation of dose distributions,” Medical Physics, Volume 25, Issue 5, May 1998, pp. 656-661.) Given a percent-dose/distance criterion (e.g., 5%-3 mm) γ is calculated for every sample point in a dose profile (1-D), image (2-D), or volume (3-D). Wherever γ<=1 the criteria is met; where γ>1 the criteria is not met.
As another example, the dose delivered to the patient 14 can be evaluated using a xi index. The xi (ξ) index is a generalization of the procedure outlined by Van Dyk et al. (1993) for treatment planning commissioning. With this method, both distributions be compared in their gradient components first, followed by a dose-difference (ΔD) and distance-to-agreement (DTA) analysis. Since there are two dose distributions and two dose gradient classifications (high dose gradient or low dose gradient), there are four possible combinations. Given vref is the voxel in the reference distribution and veval is the voxel in the evaluation distribution, these combinations are:

    
    
        vref is high dose gradient, veval is high dose gradient
        vref is high dose gradient, veval is low dose gradient
        vref is low dose gradient, veval is high dose gradient
        vref is low dose gradient, veval is low dose gradient
    
    


In the proposed comparison tool, for regions in which both the reference and comparison distributions have low dose gradients, ΔD values are obtained. For all other cases, DTA analysis is done. The gradient comparison accounts for the fact that there may be a complete mismatch of dose gradients between the reconstructed and planned distributions. Once ΔD and DTA values are obtained, a numerical index for each voxel can be found that is similar the gamma index proposed by Low et al. (1998). The numerical index ξ is found by the following:




  
    
      
        
          
            ξ
            
              high
              ⁢
              
                
              
              ⁢
              gradient
              ⁢
              
                
              
              ⁢
              voxels
            
          
          =
          
            
            
              DTA
              
                DTA
                ⁢
                
                  
                
                ⁢
                tolerance
              
            
            
          
        
        ,
        
          

        
        ⁢
        
          
            ξ
            
              low
              ⁢
              
                
              
              ⁢
              gradient
              ⁢
              
                
              
              ⁢
              voxels
            
          
          =
          
            
            
              
                Δ
                ⁢
                
                  
                
                ⁢
                D
              
              
                Δ
                ⁢
                
                  
                
                ⁢
                D
                ⁢
                
                  
                
                ⁢
                tolerance
              
            
            
          
        
      
    
    
      
        (
        1
        )
      
    
  




A ξ value of one or less is considered acceptable. Though a volume can have both high and low gradient voxels, this approach is amenable to averaging or display since the ξ values are dimensionless.
After identification of the targets where there is a dose discrepancy, then new contours around the targets 38 can be defined. As such, these identified targets 38 can be evaluated, or used in the generation of new or replacement treatment plans.
The software program 90 can also include a contour module 158 operable to generate one or more contours on an image. Medical personnel can manually define a contour around a target 38 on one of the patient images based on one or more of the DVH plot(s). In another aspect, the analysis module 118 can communicate with the contour module 158 to automatically define a contour around a target 38 based on one or more of the DVH plot(s).
The software program 90 also can include a treatment delivery module 162 operable to instruct the radiation therapy treatment system 10 to deliver radiation therapy to the patient 14 according to the treatment plan. The treatment delivery module 162 can generate and transmit instructions to the gantry 18, the linear accelerator 26, the modulation device 34, and the drive system 86 to deliver radiation to the patient 14. The instructions coordinate the necessary movements of the gantry 18, the modulation device 34, and the drive system 86 to deliver the radiation beam 30 to the proper target in the proper amount as specified in the treatment plan.
The treatment delivery module 162 also calculates the appropriate pattern, position, and intensity of the radiation beam 30 to be delivered, to match the prescription as specified by the treatment plan. The pattern of the radiation beam 30 is generated by the modulation device 34, and more particularly by movement of the plurality of leaves in the multi-leaf collimator. The treatment delivery module 162 can utilize canonical, predetermined or template leaf patterns to generate the appropriate pattern for the radiation beam 30 based on the treatment parameters. The treatment delivery module 162 can also include a library of patterns for typical cases that can be accessed in which to compare the present patient data to determine the pattern for the radiation beam 30.
FIG. 9 illustrates a flow chart of a method of generating contour structures using a dose volume histogram. Medical personnel interact with the software program 90 to generate (at 200) a dose volume histogram of a target 38 of the patient 14. The DVH is typically displayed as an image on a computer monitor connected to the system 10. In one aspect, the dose volume histogram is generated to evaluate the success of the treatment plan. In this aspect, medical personnel interact with the software program 90 to select (at 204) a subset on the displayed image of the dose volume histogram to identify areas of dose discrepancy on a dose map image which corresponds to the selected subset. Medical personnel can select the subset on the displayed image with a mouse, touch pad, or other drawing based recognition system. Based on the selected subset of the dose volume histogram, the software program 90 displays (at 208) the corresponding subset of the dose map image to the medical personnel. In some aspects, the software program 90 can generate (at 212) new contours on the dose map image that better correspond to the dose distribution of the target 38.
FIG. 10 illustrates a flow chart of a method of generating contour structures using a dose volume histogram. Medical personnel generate (at 250) a treatment plan, which includes a first dose volume of a planned radiation dose for the patient 14. After delivery of the treatment plan, the analysis module 118 determines (at 254) a second dose volume which indicates an amount of radiation delivered to the patient 14 during the treatment. Medical personnel further interact with the analysis module 118 to compare (at 258) the first dose volume and the second dose volume and to generate (at 262) a dose volume histogram on the system display/monitor of the resulting comparison. Medical personnel further interact with the analysis module 118 to select (at 266) a subset on the displayed image of the dose volume histogram to identify areas of dose discrepancy on a dose map image which corresponds to the selected subset. Medical personnel can select the subset on the displayed image with a mouse, touch pad, or other drawing based recognition system. Based on the selected subset on the dose volume histogram, the software program 90 displays (at 270) the corresponding subset of the dose map image to the medical personnel. In some aspects, the software program 90 can generate (at 274) new contour(s) on the dose map image that better correspond to the dose distribution of the target 38.
Various features and advantages of the invention are set forth in the following claims.

## Claims

1. A method of defining a new region of interest for an existing region of interest using a dose volume histogram, the method comprising using a computer to carry out the steps of:
generating a dose volume histogram of radiation dose for a pre-existing region of interest;
selecting a subset of the dose volume histogram; and
defining a new region of interest that corresponds to the selected subset of the dose volume histogram.

2. A method as set forth in claim 1 and further comprising displaying a region on an image that corresponds to the selected subset of the dose volume histogram.

3. A method as set forth in claim 1 wherein the radiation dose is a dose delivered in one or more previous treatments.

4. A method as set forth in claim 1 wherein the radiation dose is a planned dose to be delivered to the patient.

5. A method as set forth in claim 1 and further comprising generating a treatment plan for the patient and wherein the new region of interest is used to modify the treatment plan.

6. A method as set forth in claim 1 wherein the new region of interest is an updated version of the existing region of interest.

7. A method as set forth in claim 1 wherein the radiation dose is a combination of a planned radiation dose to be delivered to the patient and a radiation dose previously delivered to the patient.

8. A method as set forth in claim 1 wherein the image is a dose map of a portion of the patient.

9. A method as set forth in claim 1 and further comprising adapting a treatment plan for the patient based on the new region of interest.

10. A method of defining a new region of interest for an existing region of interest using a dose volume histogram, the method comprising using a computer to carry out the steps of:
generating a dose volume histogram of radiation dose for a pre-existing region of interest;
selecting a subset of the dose volume histogram; and

defining a new region of interest that corresponds to the selected subset of the dose volume histogram,
wherein the dose volume histogram is a dose volume histogram of a comparison between at least two dose volumes.

11. A method as set forth in claim 10 wherein one of the dose volumes is a planned radiation dose to be delivered to the patient.

12. A method as set forth in claim 10 wherein one of the dose volumes is a radiation dose previously delivered to the patient.

13. A method as set forth in claim 10 wherein one of the dose volumes is a combination of a planned radiation dose to be delivered to the patient and a radiation dose previously delivered to the patient.

14. A method as set forth in claim 10 wherein one of the dose volumes is one of a sum of or difference between previously delivered doses.

15. A method comprising using a computer to carry out the steps of:
generating a first dose volume representing a first radiation dose for a patient;
generating a second dose volume representing a second radiation dose for the patient;
comparing the first dose volume and the second dose volume;
generating a dose volume histogram based on the comparison;
selecting a subset on the dose volume histogram; and
generating a region of interest based on the selected subset.

16. The method as set forth in claim 15 wherein the comparison is a difference between the first radiation dose and the second radiation dose.

17. The method as set forth in claim 16 wherein the first radiation dose is a planned dose and the second radiation dose is a delivered dose.

18. The method as set forth in claim 15 wherein the region of interest is automatically generated.

19. The method as set forth in claim 15 wherein the delivered radiation dose is a sum of a plurality of delivered doses.

20. The method as set forth in claim 19 wherein the delivered doses are summed using deformation.

21. The method as set forth in claim 15 and further comprising generating a treatment plan for the patient and adapting the treatment plan based on the region of interest.

22. A system for generating contours using a dose volume histogram, the system comprising:
a radiation therapy treatment device including a computer processor, the radiation therapy treatment device operable to deliver a treatment plan to a patient; and
a software program stored in a computer readable medium accessible by the computer processor, the software being operable to generate a dose volume histogram of radiation dose for a pre-existing region of interest, select a subset of the dose volume histogram, and define a new region of interest that corresponds to the selected subset of the dose volume histogram.

23. The system as set forth in claim 22 wherein the software program includes an analysis module operable to generate the dose volume histogram of the patient radiation therapy dose.

24. The system as set forth in claim 22 wherein the software program includes a contour module operable to generate a contour on the image that corresponds to the dose volume histogram.

25. The system as set forth in claim 22 wherein the software program is further operable to generate a treatment plan and modify the treatment plan based on the new region of interest.

26. A method of defining a new region of interest using a dose volume histogram, the method comprising using a computer to carry out the steps of:
generating a first dose volume;
generating a second dose volume;
comparing the first dose volume and the second dose volume;
generating a histogram based on the comparison;
selecting a subset on the histogram; and
generating a region of interest based on the selected subset.

27. The method as set forth in claim 26 wherein the comparison is a difference between the first dose volume and the second dose volume.

28. The method as set forth in claim 26 wherein the region of interest is automatically generated.

29. The method as set forth in claim 26 and further comprising generating a treatment plan for the patient and adapting the treatment plan based on the region of interest.

30. The method as set forth in claim 26 wherein the comparison is based on a gamma index.

31. The method as set forth in claim 26 wherein the comparison is based on a xi function.

32. A method of defining a new region of interest using a histogram, the method comprising using a computer to carry out the steps of:
generating a histogram of radiation dose for a pre-existing region of interest;
selecting a subset of the histogram; and
defining a new region of interest that corresponds to the selected subset of the histogram.

33. A method as set forth in claim 32 wherein the histogram is a dose volume histogram.

34. A method as set forth in claim 32 and further comprising displaying a region on an image that corresponds to the selected subset of the histogram.

35. A method as set forth in claim 32 wherein the radiation dose is a dose delivered in one or more previous treatments.

36. A method as set forth in claim 32 wherein the radiation dose is a planned dose to be delivered to the patient.

37. A method as set forth in claim 32 and further comprising generating a treatment plan for the patient and wherein the new region of interest is used to modify the treatment plan.

38. A method as set forth in claim 32 wherein the new region of interest is an updated version of the existing region of interest.

39. A method as set forth in claim 32 wherein the radiation dose is a combination of a planned radiation dose to be delivered to the patient and a radiation dose previously delivered to the patient.

40. A method as set forth in claim 32 and further comprising adapting a treatment plan for the patient based on the new region of interest.

41. A method as set forth in claim 32 wherein the image is a dose map of a portion of the patient.

42. A method of defining a new region of interest using a histogram, the method comprising using a computer to carry out the steps of:
generating a histogram of radiation dose for a pre-existing region of interest;
selecting a subset of the histogram; and
defining a new region of interest that corresponds to the selected subset of the histogram, wherein the histogram is a dose volume histogram of a comparison between at least two dose volumes.

43. A method as set forth in claim 42 wherein one of the dose volumes is a planned radiation dose to be delivered to the patient.

44. A method as set forth in claim 42 wherein one of the dose volumes is a radiation dose previously delivered to the patient.

45. A method as set forth in claim 42 wherein one of the dose volumes is a combination of a planned radiation dose to be delivered to the patient and a radiation dose previously delivered to the patient.

46. A method as set forth in claim 42 wherein one of the dose volumes is one of a sum of or difference between previously delivered doses.