Abstract:
A radiation dosimetry quality assurance system is disclosed that includes a three-dimensional (3D) phantom extending along a longitudinal axis to form an exterior surface and an interior volume and a passage formed to extend into the interior volume of the 3D phantom to removeably receive a detector array therein. The system also includes an angular-compensation system coupled to the exterior surface of the 3D phantom and having a physical contour extending from the exterior surface of the 3D phantom and configured to control an angular dependence of the detector array during measurement of the actual radiation dose delivered by the radiation delivery system. The system further includes a detector-angle adjustment system configured to allow selection of a relative position of the detector array with respect to a radiation source of the radiation delivery system during measurement of the actual radiation dose delivered during the planned medical process.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to radiation systems and methods and, more particularly, relates to systems and methods for improved radiation dosimetry using a customizable three dimensional (3D) dosimetry phantom. 
     Radiation as a source for acquiring medical imaging data and delivering therapy has become a mainstay of modern medicine. In either clinical setting, but particularly radiation therapy, radiation is delivered to a defined target volume, generally a specifically designated portion of a patient. In radiation therapy, where the delivered dose is substantially higher than imaging applications, effort is made to deliver the radiation dose in such a manner that the healthy tissue surrounding the target tissues does not receive radiation doses in excess of desired tolerances. In order to achieve this control of the imparted dose to the subject, highly accurate radiation delivery techniques are required. Many factors provide difficulties in obtaining the desired level of accuracy, including differences between the planned and delivered dose distributions and uncertainty in subject position with respect to the treatment system. 
     Conventional external beam radiation therapy is commonly administered by directing a linear accelerator (“linac”) to produce beams of ionizing radiation that irradiate the defined target volume in a patient. The radiation beam is a single beam of radiation that is delivered to the target region from several different directions, or beam paths. Together, the determination of how much dose to deliver along each of these beam paths constitutes the so-called radiation therapy “plan.” The purpose of the treatment plan is to accurately identify and localize the target volume in the patient that is to be treated. This technique is well established and is generally quick and reliable. 
     Intensity modulated radiation therapy (“IMRT”) is an external beam radiation therapy technique that utilizes computer planning software to produce a three-dimensional radiation dose map, specific to a target tumor&#39;s shape, location, and motion characteristics. IMRT treats a patient with multiple rays of radiation, each of which may be independently controlled in intensity and energy. Because of the high level of precision required for IMRT methods, detailed data must be gathered about tumor locations and their motion characteristics. In doing so, the radiation dose imparted to healthy tissue can be reduced while the dose imparted to the affected region, such as a tumor, can be increased. In order to achieve this, accurate geometric precision is required during the treatment planning stage. Thus, while conventional IMRT methods have had success in increasing the effective dose imparted to the defined target volume while mitigating the imparted radiation dose to the surrounding healthy tissue, further reduction of the radiobiological effect on healthy tissue is desirable. 
     Image-guided radiation therapy (“IGRT”) employs medical imaging, such as computed tomography (“CT”), concurrently with the delivery of radiation to a subject undergoing treatment. In general, IGRT is employed to accurately direct radiation therapy using positional information from the medical images to supplement a prescribed radiation delivery plan. The advantage of using IGRT is twofold. First, it provides a means for improved accuracy of the radiation field placement. Second, it provides a method for reducing the dose imparted to healthy tissue during treatment. Moreover, the improved accuracy in the delivery of the radiation field allows for dose escalation in the tumor, while mitigating dose levels in the surrounding healthy tissue. The concern remains, however, that some high-dose treatments may be limited by the radiation toxicity capacity of healthy tissues that lay close to the target tumor volume. 
     However, despite the progressive sophistication in the systems methods for planning and delivering radiation therapy, there is still a substantial potential for the subject to receive undesired radiation doses. In particular, despite the ability to create complex treatment plans where 3D dose distributions are highly customized for each patient, there is a substantial potential for the actual dose delivered to be greater than the planned dose or to be received by the patient in a manner different than that simulated in the plan. 
     One reason for this undesired potential is a low availability/high cost of systems and methods to verify the radiation dose prior to or during the treatment. Another, more prevalent reason for this undesired potential is a substantial lack of systems and methods that allow for customized measurement and analysis of dose in critical regions of interest. 
     For example, many of the sophisticated radiation therapy modalities mentioned above feature rotational therapy where it is desirable to use a 3D phantom instead of the very common 2D arrays that are used for static gantry angle IMRT. However, such 3D phantoms generally fall into one of two categories: 3D phantoms coupled with 2D detection arrays and 3D phantoms coupled with 3D detection systems. 
     In a first case, some have attempted to employ commonly-available 2D radiation detection arrays inserted into fixed “3D” phantoms. In these cases, though the phantom extends along the three planes (sagittal, coronal, and transverse) corresponding to those planes of a subject, due to the use of a 2D detection array, these systems are only capable of measuring dose along the one plane along which the 2D detection array extends. Furthermore, these systems are plagued by inaccuracies associated with problems of angular dependence. That is, it is known that the 2D detection arrays have a substantial change in sensitivity with variations in the angle of incidence of radiation on the 2D detection array. Thus, the angular dependence of the 2D detection array limits the accuracy of these systems. 
     Some have recognized the limitations of these systems combining 3D phantoms with 2D detection arrays and, in a second case, have developed 3D dosimetry arrays that are combined with 3D phantoms in a fixed dose detector arrangement. However, these systems are expensive and have limited, if not entirely very unsuitable, detector placement. Thus, though such systems are quite sophisticated, they still present substantial limits on practical clinical use in per-patient dose quality assurance (QA). 
     It would therefore be desirable to provide a system and method for QA in radiation dosimetry that provides greater flexibility without increases in overall system costs or complexity. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned drawbacks by providing a system and method for utilizing available detector arrays with a highly configurable 3D phantom to acquire accurate 3D dosimetry information. Specifically, the system and method allow user selection of a number of customizable features of the system based on a desired detector array to be used with the 3D phantom that both compensate for specific features of the desired detector array and allow the desired detector array to be utilized in a manner that improves the accuracy of the 3D dosimetry information, even when the desired detector array is a 2D detector array. 
     In accordance with one aspect of the invention, a radiation dosimetry quality assurance system is disclosed that is configured to measure an actual radiation dose delivered by a radiation delivery system during a planned medical process. The radiation dosimetry quality assurance system includes a three-dimensional (3D) phantom extending from a first end to a second end along a longitudinal axis to form an exterior surface and an interior volume and a passage formed to extend into the interior volume of the 3D phantom to removeably receive a detector array therein. The system also includes an angular-compensation system coupled to the exterior surface of the 3D phantom and having a physical contour extending from the exterior surface of the 3D phantom and configured to control an angular dependence of the detector array during measurement of the actual radiation dose delivered by the radiation delivery system during the planned medical process. The system further includes a detector-angle adjustment system configured to allow selection of a relative position of the detector array with respect to a radiation source of the radiation delivery system during measurement of the actual radiation dose delivered by the radiation delivery system during the planned medical process. 
     In accordance with another aspect of the invention, a radiation dosimetry quality assurance system is disclosed that is configured to measure an actual radiation dose delivered by a radiation delivery system during a planned medical process. The radiation dosimetry quality assurance system includes a three-dimensional (3D) phantom extending from a first end to a second end along a longitudinal axis to form an exterior surface and an interior volume and a passage formed to extend into the interior volume of the 3D phantom. An adapter system is configured to receive a detector array having a predetermined geometry and configured to removeably couple the detector array within the passage. The system also includes an angular-compensation system coupled to the exterior surface of the 3D phantom to control an angular dependence of the detector array during measurement of the actual radiation dose delivered by the radiation delivery system during the planned medical process. The system further includes a detector-angle adjustment system configured to allow selection of relative position(s) of the detector array with respect to radiation source(s) of the radiation delivery system during measurement of the actual radiation dose delivered by the radiation delivery system during the planned medical process and a processor configured to receive the measure of the actual radiation dose delivered by the radiation source during the planned medical process from the detector array and generate 3D dosimetry information therefrom. 
     The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary image-guided radiation therapy (“IGRT”) system and, associated therewith, a quality assurance dosimetry system in accordance with the present invention including customizable 3D dosimetry phantom. 
         FIG. 2  is a perspective view of the customizable 3D dosimetry phantom of  FIG. 1  in accordance with the present invention. 
         FIG. 3  is an elevational view of another configuration of the customizable 3D dosimetry phantom in accordance with the present invention. 
         FIG. 4  is a flow chart setting forth the steps of a method for using the quality assurance dosimetry system in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an exemplary image-guided radiation therapy (IGRT) system  100  is illustrated. The succeeding description of the invention is made with respect to the IGRT system  100 ; however, it should be readily appreciated by those skilled in the art that the present invention can be readily used with any number of radiation-delivery systems. For example, the present invention is readily designed for use with intensity modulated radiation therapy (IMRT) systems, stereotactic radiosurgery systems such as the CyberKnife® system (Accuray, Sunnyvale, Calif.), traditional gantry-mounted linear accelerator (“linac”) systems, and other radiation-delivery and/or imaging systems that can benefit from the use of 3D dose measurement and quality assurance (QA) capabilities. Specifically, as will be described, the present invention provides a dosimetry quality assurance (QA) system  101  that can be configured and adapted for use with any of a variety of radiation sources and can be adjusted by clinicians to perform per-patient dose QA with an accuracy and cost efficiency generally unavailable from traditional systems. 
     The illustrated IGRT system includes a therapeutic x-ray source  102  and a diagnostic x-ray source  104 . The diagnostic x-ray source  104  projects a cone-beam of x-rays toward a detector array  116 . Both the therapeutic x-ray source  102  and diagnostic x-ray source  104  are attached adjacent each other and housed at the same end of a first rotatable gantry  106 , which rotates about a pivot axis  108 . The first rotatable gantry  106  allows either of the x-ray sources,  102  and  104 , to be aligned in a desired manner with respect to the QA system  101  and, particularly, a configurable 3D phantom system  110  of the QA system  10  that is positioned on a patient table  112 . 
     A second rotatable gantry  114  is rotatably attached to the first rotatable gantry  106  such that it too is able to rotate about the pivot axis,  108 . Disposed on one end of the second rotatable gantry  114  is an x-ray detector  116 . The x-ray detector  116  functions not only as a diagnostic image device when receiving x-rays from the diagnostic x-ray source  104 , but also as a portal image device when receiving x-rays from the therapeutic x-ray source  102 . The detector array  116  is formed by a number of detector elements that together sense the projected x-rays that pass through the subject  112 . Each detector element produces an electrical signal that represents the intensity of an impinging x-ray beam and, hence, the attenuation of the beam as it passes through the subject  112 . The second rotatable gantry  114  further includes an articulating end that can pivot about three points  118 ,  120 , and  122 . The pivoting motion provided by these points  118 ,  120 , and  122 , allows the x-ray detector  116  to be moved within a two-dimensional plane. 
     The rotation of the rotatable gantries,  106  and  114 , and the operation of the x-ray sources,  102  and  104 , are governed by a control mechanism  140  of the IGRT system  100 . The control mechanism  140  includes an x-ray controller  142  that provides power and timing signals to the x-ray sources,  102  and  104 , and a gantry motor controller  144  that controls the rotational speed and position of the gantries,  106  and  114 . A data acquisition system (“DAS”)  146  in the control mechanism  140  samples analog data from detector elements and converts the data to digital signals for subsequent processing. An image reconstructor  148 , receives sampled and digitized x-ray data from the DAS  146  and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer  150  which stores the image in a mass storage device  152 . 
     The computer  150  also receives commands and scanning parameters from an operator via a console  154  that has a keyboard. An associated display  156  allows the operator to observe the reconstructed image and other data from the computer  150 . The operator supplied commands and parameters are used by the computer  150  to provide control signals and information to the DAS  146 , the x-ray controller  142  and the gantry motor controller  144 . In addition, the computer  150  operates a table motor controller  158  which controls the motorized patient table  112  to position the subject  112  within the gantries,  106  and  114 . 
     With the generalities of the IGRT system  100  serving as a general context for a radiation-delivery system, whether therapeutic or imaging, the present invention provides the aforementioned QA system  101 . As will be described, the QA system  101  includes the configurable 3D phantom  110  and a phantom control interface  160  that connects the configurable 3D phantom  110  to the computer  150  of the IGRT system  100  or another computer system. As will be described, the configurable 3D phantom  110  and phantom control interface  160  are configured to operate in conjunction with a computer system to allow operators to select customizable dosimetry detection planes, control and compensate for angular dependence of detector accuracy, and translate feedback from a 2D detector array into a 3D dosimetry QA analysis. 
     Referring now to  FIG. 2 , the configurable 3D phantom system  110  of the present invention is illustrated in further detail. Specifically, the configurable 3D phantom system  110  includes a base phantom unit  200  that, as illustrated, may be formed as a cylinder or other shape, such as the oval-shaped cylinder of  FIG. 3 . Particularly when formed as a cylinder, the base phantom unit  200  may be accompanied by a rack or other support system  202  to allow the base phantom unit  200  to be advantageously positioned on the patient table of a radiation delivery system, such as illustrated in  FIG. 1 . However, as also illustrated in  FIG. 3 , the support system  202  may also be utilized with other advantageous shapes. Regardless of the particular shape of the base phantom unit  200 , the 3D design of the base phantom unit  200  defines an exterior surface  201  and interior volume  203 . 
     The base phantom unit  200  of the configurable 3D phantom system  110  is designed to receive any of a plethora of commercially-available 2D detector arrays  204 . To facilitate coupling the variety of shapes, sizes, and designs of commercially-available 2D detector arrays  204 , an adapter system  206  is provided. The adapter system  206  is formed by a plurality of interchangeable adapters having respective openings  208  configured to receive one of the commercially-available 2D detector arrays  204 . Accordingly, regardless of the specific dimensions or configuration of a particular 2D detector array  204 , a proper adapter system  106  can be used to couple the 2D detector array  204  with the base phantom unit  200  by positioning the particular 2D detector array  204  in the adapter system  206  through the opening  208  and positioning the combined 2D detector array  204  and adapter system  206  in a detector opening  210  formed in the base phantom unit  200 . By providing a configurable 3D phantom system  110  that is capable of utilizing any of a variety of common 2D detector arrays  204 , the configurable 3D phantom system  110  provides 3D QA capabilities at a fraction of the cost of dedicated 3D phantom systems having integrated 3D detector arrays. Furthermore, it provides the operator and maintenance staff with substantially greater flexibility and interoperability. Though illustrated as being designed to receive a 2D detector array  204  and 2D adapter system  206 , it is contemplated that the base phantom unit  200  may include any of a variety of openings  210  configured to receive differing detector arrays  204  and associated adapter systems  206 , including 3D detector geometries. 
     Beyond being customizable to receive any of a variety of detector arrays, the base phantom unit  200  may also include an angular-compensation system  212 . The angular-compensation system  212  may be formed by a plurality of selected and, if desired, interchangeable angular dose-shaping wings  214 ,  216 ,  218 . The dose-shaping wings  214 ,  216 ,  218  are designed to be coupled in pairs with the base phantom unit  200  to correct for the angular dependence of the particular detector array  214  that is coupled, through the adapter system  206 , with the base phantom unit  200 . Thus, preferably, the dose-shaping wings  214 ,  216 ,  218  are selected, along with the adapter system  206 , based on the detector array  204  selected for coupling with the customizable 3D phantom system  110 . 
     In addition to providing systems for correcting the angular dependence of a particular, selected detector array  204 , the customizable 3D phantom system  110  includes a dynamically-adjustable, detector-angle system  219  designed to facilitate user-selection of optimized measurement planes within which to arrange the detector array  204 . This is achieved by allowing user selection and adjustment of the relative position of the detector array  204  about a longitudinal axis  220  of the base phantom unit  200 . As illustrated in  FIG. 2 , this user selection and adjustment can be achieved by rotating the base phantom unit  200  relative to the support system  202 , such that the plane formed by the detector array  204  is rotated about a central axis formed by the longitudinal axis  220  of the base phantom unit  200 . To assist in tracking the relative position of the measurement plane of the detector array  204  when being adjusted, it is contemplated that the support system  202  may include a reference indicator  222  configured to provide an indication of relative position relative to a plurality of angular markers  224  formed on the base phantom unit  200 , or vice versa. 
     However, the configuration described with respect to  FIG. 2  is but one system designed to facilitate user-selection of optimized measurement planes within which to arrange the detector array  204 . For example, it is contemplated that the base phantom unit  200  may include an inner cylinder  226  configured to rotate within an outer shell  228 . In this regard, it is contemplated that control and/or monitoring of the relative position of the detector array  204  may be performed automatically, for example, under computerized control. Whether or not automated, a positional indicator  230  and angular markers  232  may be provided, such as through indicators positioned on or about the inner cylinder  226  and outer shell  228 . 
     Referring now to  FIG. 4 , the general steps of a process for radiation delivery QA in accordance with the present invention are provided in a flow chart. The process begins at process block  300  by selecting a desired configuration of the above-described customizable 3D phantom. This step may take a variety of forms depending on the clinical setting and general resources available to the operator. For example, in some cases, the selection at process block  300  may be performed when purchasing the above-described customizable phantom. For example, during the purchasing of the QA system or the customizable 3D phantom, one may indicate the particular detector array intended for use with the QA system and the customizable 3D phantom. As such, the proper adapter and angular-compensation systems can be provided to couple the particular detector array with the customizable 3D phantom and compensate for the particular angular dependence of the selected detector array. Alternatively, of course, a plurality of adapter and angular-compensation systems may be readily available to the operator to then chose which adapter and angular-compensation systems to couple to the customizable 3D phantom based on the detector array. 
     Once the customizable 3D phantom has been properly coupled with a selected detector array and corresponding adapter and angular-compensation systems, at process block  302 , the operator selects the desired angles for the detection plane based on the plan that will be evaluated using the QA system. As described above, this can be achieved by, for example, rotating the customizable 3D phantom in the support system or, if provided, by rotating an inner portion of the customizable 3D phantom within an outer portion of the customizable 3D phantom. In either case, the selection process performed in conjunction with process block  302  may be performed manually or with automated assistance, or may be performed in a fully automated fashion. In the manual case, the operator may rotate the detection plane as described above to a desired angle. In the case of automated assistance or a fully automated process, the computer and control systems associated with the QA system may suggest or automatically select a desired angle for the detection plane based on the specifics of the radiation delivery procedure that are planned. 
     Thereafter, at process block  304 , the radiation delivery plan is calculated and, at process block  306 , the actual dose received by the customizable 3D phantom is measured. Using the acquired measurements, at process block  308 , an associated computer system transforms the measured dose positions/values into a 3D dose coordinate system matching what was previously calculated by the Treatment Planning System (TPS) in step  304 . Thereafter, at process block  310 , the measurements and calculations may be analyzed to generate metrics of accuracy pertaining to the radiation delivery plan. 
     Accordingly, a system and method are provided that permits user customizable angles of the dosimetry detection plane, physically controls the effects of angular dependence of detection arrays, and is capable of utilizing cost-effective and readily available 2D detector arrays and translating the acquired information into 3D information to thereby overcome the need to invest in costly, dedicated 3D detector arrays, unless desired. Unlike some traditional systems that provide multiple angles of the dosimetry detection plane by simply utilizing multiple detector arrays, for example in a “cross” configuration, the present invention provides the desired ability to use multiple angles of the dosimetry detection plane, without the cost associated with multiple, dedicated detector arrays in a fixed configuration. Similarly, while some systems may permit small ranges or fixed positions through which the angle of the dosimetry detection plane can be adjusted, the present invention provides a highly adjustable system that, for example, can provide an operator with a continuous range and continuously variable number of angles through which the dosimetry detection plane can be adjusted. Further still, many systems simply ignore the challenges of angular dependence of detector arrays and some systems have attempted to overcome these challenges by forming large, for example, cylindrical detector arrays or have included “shaping features,” such as air pockets, within a 3D phantom, these attempts to overcome the challenges of angular dependence of detector arrays have substantial limitations. First, ignoring the challenges of angular dependence of detector arrays, particularly 2D detector arrays, reduces the effectiveness of any QA system and, in particular, seems to be counterproductive to an expressed goal of true quality assurance. Second, large, shaped, for example cylindrical, detector arrays are quite costly to manufacture and maintain. Finally, internally arranged, “shaping features,” such as air pockets, limit the versatility of the 3D phantom substantially. For example, the necessary fixed position of the “shaping features” with respect to the detector array retrains the ability to perform any adjustment of the angle of the dosimetry detection plane. Similarly, these internal “shaping features” are designed very specifically to the particular angular dependence of the associated detector array and cannot be readily adjusted or reviewed/considered by the operator. 
     The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.