Large-volume scintillator detector for rapid real-time 3-D dose imaging of advanced radiation therapy modalities

Abstract

An apparatus and method for measuring three-dimensional radiation dose distributions with high spatial and temporal resolution using a large-volume scintillator. The scintillator converts the radiation dose distribution into a visible light distribution. The visible light is transported to one or more photo-detectors, which measure the light intensity. The light signals are processed to correct for optical artifacts, and the three-dimensional light distribution is reconstructed. The reconstructed light distribution is post-processed to convert light amplitudes to measured radiation doses. The high temporal resolution of the detector makes it possible to observe the evolution of a dynamic dose distribution as it changes over time. Integral dose distributions can be measured by summing the dose over time.

Claims

1. A radiation dose detector device, comprising: a scintillating element; a plurality of light detectors configured to detect light emitted from the scintillating element, wherein: the plurality of light detectors are coupled to a housing extending around the scintillating element; each light detector of the plurality of light detectors comprises a field of view; the entire scintillating element is in the field of view of each light detector of the plurality of light detectors; and a computer, wherein the computer is configured to receive data from the plurality of light detectors and configured to generate a three-dimensional map of light emitted from the scintillating element.

2. The radiation dose detector device of claim 1 wherein the plurality of light detectors are configured to simultaneously detect light emitted from the scintillating element.

3. The radiation dose detector device of claim 1 wherein at least one of the plurality of light detectors are selected from the group consisting of: charge-coupled device (CCD) cameras, complementary metal-oxide sensor (CMOS) cameras, light field cameras, photodiode arrays and photomultiplier tube arrays.

4. The radiation dose detector device of claim 1 wherein the plurality of light detectors are coupled to a housing, wherein the housing is configured to block external light from entering the radiation dose detector.

5. The radiation dose detector device of claim 1 further comprising a collimator between the scintillating element and at least one of the plurality of light detectors.

6. The radiation dose detector device of claim 1 further comprising one or more optical fibers between the scintillating element and at least one of the plurality of light detectors.

7. The radiation dose detector device of claim 1 wherein the computer comprises a computer readable medium comprising software configured to execute a pre-processing algorithm, a tomographic reconstruction algorithm and a post-processing algorithm.

8. The radiation dose detector device of claim 7 wherein the pre-processing algorithm is configured to correct for both optical and dosimetric artifacts.

9. The radiation dose detector device of claim 7 wherein the tomographic reconstruction algorithm converts data received from the plurality of light detectors into a three-dimensional dose distribution.

10. The radiation dose detector device of claim 9 wherein the tomographic reconstruction algorithm comprises a filtered backprojection algorithm.

11. The radiation dose detector device of claim 9 wherein the tomographic reconstruction algorithm comprises an iterative algorithm.

12. The radiation dose detector device of claim 7 wherein the post-processing algorithm is configured to convert grayscale levels of three-dimensional light distribution into actual dose values by comparison with a reference measurement.

13. A three-dimensional radiation dose detector device, comprising: a continuous volumetric scintillating element; and means for measuring the light emission from said scintillating element from multiple positions or directions simultaneously and with high temporal resolution, wherein: said means for measuring the light emission from said scintillating element is positioned around said scintillating element; said means for measuring the light emission from said scintillating element comprises a depth of field that extends through said scintillating element.

14. The radiation dose detector device of claim 13 wherein the continuous volumetric scintillating element has a volume of about 500 to 15,000 cubic centimeters.

15. The radiation dose detector device of claim 13 wherein the temporal resolution is up to 100 samples per second.

16. The radiation dose detector device of claim 13, wherein said scintillating element is an organic or inorganic material in solid, liquid, or gelatinous state.

17. The radiation dose detector device of claim 13, wherein said means for measuring light emission comprises one or more charge-coupled devices, complementary metal-oxide-semiconductor devices, light field cameras, photomultiplier tubes, photodiodes, avalanche photodiodes.

18. The radiation dose detector device of claim 13, wherein said means of measuring light emission comprises one or more light-field imagers or plenoptic cameras.

19. The radiation dose detector of claim 13, wherein said means for measuring light emission includes detectors equally spaced at an angle , with the sum of all angles equal to 360 degrees.

20. The radiation dose detector device of claim 13, wherein said means for measuring light emission includes detectors unequally-spaced at angles i, where the sum of all i equals 360 degrees or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a 3D detector system using a cylindrical plastic scintillator encased in an elliptic cylinder encasing body. Scintillation light is collected by arrays of CCD cameras. A gap in the ring of cameras is left to allow for delivery of the radiation beam.

(2) FIG. 2 shows a 3D detector system using a cylindrical plastic scintillator encased in an elliptic cylinder encasing body. Scintillation light is collected by a few CCD cameras. Mirrors are used to redirect light exiting the phantom at various angles toward the cameras.

(3) FIG. 3 shows a 3D detector system using a cylindrical plastic scintillator encased into an elliptic cylinder encasing body. Scintillation light is collected by arrays of photodetectors. A gap is left to allow for delivery of the radiation beam.

(4) FIG. 4 shows a 3D detector system using a cylindrical plastic scintillator with no encasing body. This embodiment utilizes a single CCD camera, which is attached to a track surrounding the cylindrical surface of the plastic scintillator. The housing may be moved along the track by means of a motor, allowing the camera to view the detector from multiple angles.

(5) FIG. 5 shows a 3D detector system using a cylindrical plastic scintillator encased in an elliptical encasing body. Light is collected by bundles of optical fibers with low numerical aperture. The optical fibers are then directed toward photo-detectors such as CCD cameras.

(6) FIG. 6 shows a 3D representation of a detector system using a fiber optic bundle. Only a single fiber optic bundle is shown for clarity. In this case, a cylindrical scintillator sensitive volume is encased in an octagonal phantom (encasing body).

(7) FIG. 7 shows a 3D detector system using a cylindrical plastic scintillator with no encasing body. Light is collected by one or two light field cameras facing the flat ends of the cylindrical plastic scintillator.

(8) FIG. 8 shows a 3D detector system using a cylindrical plastic scintillator inside an encasing body in the shape of a part of the human anatomy. Light is collected by a light field camera facing a flat face of the encasing body.

(9) FIG. 9 shows a 3D detector system using a transparent cylindrical tank filled with liquid or gelatinous scintillator material. A stand is provided within the tank for the placement of radioactive sources. The tank is surrounded by CCD cameras.

(10) FIG. 10 shows a 3D detector system using a cylindrical plastic scintillator with no encasing body. A hole is drilled through the center of the tank, whereby a radioactive source can be positioned in the center of the cylindrical plastic scintillator with a support rod. The scintillator is surrounded by CCD cameras.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(11) FIG. 1 is a schematic of one exemplary embodiment of a three dimensional (3-D) radiation detector system 100 for measuring radiation dose distributions intended for cancer treatment. A cylindrical plastic scintillator assembly 110 comprises an active element 120 in detector system 100, and in certain embodiments, the dimensions of cylindrical plastic scintillator assembly 110 include a height of approximately 10 to 30 cm and a radius of approximately 5 to 15 cm. In particular embodiments, active element 120 is encased in an elliptic cylinder encasing body 130, which is also called a phantom in the terminology of the medical physics community. In specific embodiments, the external dimensions of encasing body 130 are similar in size to a specific part of a human anatomy, including for example, a human head or human torso. In particular embodiments, encasing body 130 can be made of a clear plastic or other clear material with radiation absorption properties similar to those of water. In certain embodiments, the surface of encasing body 130 can be coated to reduce or prevent light reflection.

(12) In the embodiment shown in FIG. 1, encasing body 130 is surrounded by a plurality of light detectors 140. In specific embodiments, light detectors 140 may comprise CCD cameras positioned at regular angles around the curved face of the elliptic cylinder volume. In the specific embodiment shown FIG. 1, seven cameras are shown at intervals of 45 degrees with one interval forming a gap 150 of 90 degrees. Gap 150 can be left in the regular spacing of light detectors 140 to allow a radiation beam to be delivered through the curved side of encasing body 130. In particular embodiments, light detectors 140 can be coupled to encasing body 130 by a housing 170 made of suitable material, e.g. metal or plastic. Housing 170 can rigidly maintain the positions of light detectors 140 while also blocking external light from entering the system. The distance between the surface of encasing body 130 and light detectors 140 can be between 20 cm and 50 cm in certain embodiments.

(13) In specific embodiments, light detectors 140 may be CCD cameras that are fitted with low-distortion objective lenses. The lens settings can be selected such that the entire active element 120 is in the field of view of each camera, and the depth of field of each camera extends throughout the entire active element 120.

(14) In particular embodiments, a collimator grid (not shown for purposes of clarity) may be included either at the surface of encasing body 130 or in the space between encasing body 130 and light detectors 140 (e.g. between encasing body 130 and an objective lens of each camera for embodiments utilizing cameras). This collimator grid can block light that is not parallel to the axis of a light detector 140, thereby reducing scattered light and decreasing optical artifacts in the detected images.

(15) In exemplary embodiments, light detectors 140 may be configured as CCD cameras that are coupled to a computer 180 which controls the camera exposures and the data acquisition. In certain embodiments, the cameras may also be coupled to a signal provided by the radiation source to trigger the beginning and/or end of the image acquisition.

(16) The embodiment of FIG. 1 may also comprise software implementing algorithms to convert images obtained from light detectors 140 into a three-dimensional (3-D) map of the light emission inside active element 120. Certain embodiments may use the Maximum-a-posteriori (MAP) iterative reconstruction algorithm to produce a 3-D reconstruction of the light emission inside active element 120. In particular embodiments, the algorithm can incorporate corrections for optical artifacts including attenuation and scattering of the scintillation light, refraction at material interfaces, and lens aberrations.

(17) In particular embodiments, a post-processing algorithm can convert the grayscale levels of the three-dimensional dose distribution into actual dose values by comparison with a reference measurement. In the case of protons and other high-linear energy transfer (LET) radiation, a post-processing algorithm can include a method to correct for the non-linear scintillation response, or quenching, of active element 120 when exposed to radiations of varying LET. This method was developed by Birks, and is described by the equation

(18) $\begin{array}{cc}S\text{/}x=\frac{A.Math.E\text{/}x}{1+\mathrm{kB}.Math.E\text{/}x}& \left(\mathrm{equation}1\right)\end{array}$

(19) where S is the scintillation light emitted, dE/dx is the energy deposited by the protons over a distance x in the medium, A is the scintillation efficiency of the medium, and k and B are empirical factors describing the non-scintillation energy loss in the medium. The A and kB factors can be determined by calibration and are unique for each scintillator material. The reconstruction and post-processing operations can be run on a computer with a multi-core processing unit.

(20) The embodiment shown in FIG. 1 can be used to measure 3-D radiation dose distributions delivered by external beam radiation therapy equipment, including intensity-modulated photon beams and passive and scanned proton and heavy ion beams. The radiation beam can be delivered to detector 110 through gap 150 or, in specific embodiments, through flat faces of an elliptic cylinder-shaped encasing body 130. Encasing body 130 provides attenuation to radiation beam 160 in a manner similar to the tissues of a human body, so that the radiation dose measured in active element 120 is similar to the dose delivered to a similarly-located region inside a patient. The scintillator material can convert the radiation in the form of high-energy x-rays or particles into visible light, which is emitted isotropically from the location of energy deposition.

(21) In certain exemplary embodiments, light emitted by active element 120 passes through encasing body 130 and reaches light detectors 140. In particular embodiments, the acquisitions of light detectors 140 are simultaneous and can be triggered manually or automatically through the software interface, or by signals from the radiation delivery machine. Light detectors 140 may make one long acquisition to measure all of the light delivered by the radiation source, or they may rapidly acquire many images during the course of the radiation delivery. These acquisitions may be timed to align with times that the radiation is being delivered so that no (or minimal) signal is lost between camera frames in particular embodiments. In certain embodiments, the control software may also be used to send signals to cameras and the radiation delivery machine in order to trigger the radiation delivery and camera acquisition at the same time in a controlled manner.

(22) In particular embodiments, the image data can be downloaded from light detectors 140 to the control computer, where it is processed by the 3-D reconstruction software to convert the images into a 3D map of the scintillation light intensity inside of active element 120. This software can use the maximum-a-posteriori (MAP) iterative reconstruction scheme using the one step late (OSL) algorithm to perform the reconstruction. The projection operators in the MAP algorithm include correction factors for light scattering, attenuation, noise, and refraction at material boundaries.

(23) In certain embodiments, a post-processing algorithm uses a calibrated conversion factor to convert the reconstructed light signal into units of radiation dose to active element 120 of detector 110. In the case of irradiation by proton or heavy ion beams or other high-linear energy transfer (LET) radiation, the light distribution can be corrected for quenching, which is a non-linear response of scintillating materials to variations in the LET of the incident radiation. The quenching correction method can use equation 1 (provided above) with empirical factors provided by calibration measurements for the scintillating material. The term dE/dx can be obtained from Monte Carlo calculations of the specific proton or heavy ion beamline. These calculations provide a mapping of dE/dx to the beam energy and the depth in the material. This mapping can be used to assign the proper dE/dx value to each voxel in the reconstructed light distribution. After quenching correction is completed, the calibrated conversion factor can be applied to convert the corrected 3-D light distribution into a 3-D dose distribution.

(24) FIG. 2 shows a 3-D detector system 200 using a cylindrical plastic scintillator assembly 210 comprising an active element 220 encased in an elliptic cylinder encasing body 230. In this embodiment, light is collected by a fewer number of light detectors 240, and mirrors are used to redirect light exiting body 230 at various angles toward light detectors 240. This embodiment is generally equivalent to the embodiment shown in FIG. 1, except that a smaller number of light detectors 240 is used (FIG. 2 shows three detectors), and the number of viewing angles is increased by using mirrors 245 to redirect light from areas that would otherwise not be measured by light detectors 240. In this embodiment, mirrors are enclosed in housing 270. Light detectors 240 are directed so that part of the detected image is formed by light traveling directly from active element 220, while another section of the same image is formed by light traveling from a different direction and redirected by a mirror 245.

(25) In the embodiment shown in FIG. 2, the reconstruction algorithm is the same as in the first embodiment, except that each image is segmented into the direct and reflected image, and the reflected image is projected from the appropriate direction in the reconstruction algorithm.

(26) FIG. 3 shows a 3D detector system 300 using a cylindrical plastic scintillator assembly 310 comprising an active element 320 encased into an elliptic cylinder encasing body 330. This detector system is similar to that described in the embodiment of FIG. 1, except that the light detectors are specifically configured as arrays of photodetectors 340, including for example, photodiodes. Photodetector arrays 340 may be positioned in the same locations as the light detectors 140 in the embodiment of FIG. 1, with or without collimators. Additionally, photodetector arrays 340 may be attached directly to the surface of the encasing body 330 or to a collimator on the surface of encasing body 330. Such a design can provide a more compact device and decrease artifacts caused by refraction.

(27) FIG. 4 shows a 3-D detector system 400 using a cylindrical plastic scintillator 410. In this embodiment, there is no encasing body and scintillator 410 is expanded to comprise the entire bulk of the phantom component of the detector. In this embodiment, the entire phantom is the active volume, and radiation dose measurements may be acquired throughout the entire phantom volume.

(28) This embodiment utilizes a light detector 440 coupled to a housing 470, which is in turn coupled to a track 475 surrounding the cylindrical surface of a plastic scintillator 410. In certain embodiments, light detector 440 may be configured as a single CCD camera. Housing 470 may be moved along track 475 by means of a motor 485. This can allow light detector 440 to view scintillator 410 from multiple angles.

(29) The operation of this embodiment is similar to the embodiment of FIG. 1, but instead of acquiring images from multiple images simultaneously through multiple detectors, images can be acquired sequentially, with motor 485 moving light detector 440 to a different position for each image. By repeating the dose delivery at several light detector positions, a 3-D map of the radiation dose can be reconstructed using only one light detector 440.

(30) FIG. 5 shows a 3-D detector system 500 using a cylindrical plastic scintillator assembly 510 comprising an active element 520 encased in an elliptical encasing body 530. In this embodiment, light can be collected by light detectors 540 configured as bundles of optical fibers 542 directed toward photo-detectors 544 (e.g. CCD cameras), where the light signals are recorded. In particular embodiments, optical fibers 542 have a low numerical aperture. The 3-D light emission reconstruction can be accomplished by mapping the signal from each optical fiber 542 to its location on encasing body 530 and using an iterative or backprojection algorithm to reconstruct the 3-D light emission.

(31) FIG. 6 shows a schematic perspective view of a detector system 600 comprising a fiber optic bundle 642. In the embodiment shown in FIG. 6, only a single fiber optic bundle 642 is shown for clarity. It is understood that exemplary embodiments may comprise multiple fiber optic bundles. In this embodiment, a cylindrical scintillator sensitive volume 620 is encased in an octagonal phantom 630. The use of an encasing body with flat faces can simplify the construction process.

(32) FIG. 7 shows a 3-D detector system 700 using a cylindrical plastic scintillator 710 with no encasing body. In this embodiment, light can be collected by one or two light detectors 740 (including for example, light field cameras) facing the flat ends of the cylindrical plastic scintillator 710. In certain embodiments, light field cameras can measure the intensity and direction of incoming light rays, making it possible to recover depth information from a single camera image and to refocus the image after it has been acquired. The 3-D reconstruction process in this embodiment may involve the refocusing of the image at multiple distances to obtain a slice of the light distribution at each focal depth. Reconstruction may also be performed by projecting the light intensity and direction back through the scintillator volume for each measured light ray.

(33) FIG. 8 shows a 3-D detector system 800 using a cylindrical plastic scintillator 810 inside an encasing body 830 in the shape of a part of the human anatomy. In particular embodiments, scintillator 810 may be fixed or removable. Scintillation light can be collected by a light detector 840 (including for example, a light field camera) facing a flat face of encasing body 830. In certain embodiments, additional light detectors may be added. In particular embodiments, light refractions caused by a curved surface of the encasing body may be corrected by applying an angle-dependent refraction calculation to the detected images or by flattening the surface of the encasing body where it is viewed by each light detector 840.

(34) FIG. 9 shows a 3-D detector system 900 using a cylindrical tank 930 filled with liquid or gelatinous scintillator material 910. In the embodiment shown, a stand 935 is provided within tank 930 for the placement of a radioactive source 915. Tank 930 can be surrounded by light detectors 940 (including for example, CCD cameras). In certain embodiments, the 3-D radiation dose distribution from source 915 can be measured by placing source 915 on stand 935 and measuring the light emission from multiple angles using light detectors 940. In particular embodiments, the dose distribution can be reconstructed from the detected images using filtered backprojection or iterative reconstruction algorithms.

(35) FIG. 10 shows a 3-D detector system 1000 using a cylindrical plastic scintillator 1010 with no encasing body. In the embodiment shown, a channel 1025 is drilled through the center of scintillator 1010, whereby a radioactive source 1015 can be positioned in the center of cylindrical plastic scintillator 1010 with a support rod 1035. In particular embodiments, channel 1025 may extend through the entire scintillator block 1010 or channel 1025 may extend halfway through. In particular embodiments, the width of channel 1025 can correspond to the width of radioactive source 1015 to be measured. In certain embodiments, the width of the channel 1025 can be slightly larger than a catheter used with a high-dose-rate brachytherapy robotic afterloader. Scintillator 1010 can be surrounded by light detectors 1040 (including for example, CCD cameras). In certain embodiments, radioactive source 1015 can placed in channel 1025 either using a catheter and robotic afterloader or by placing the source inside the hole and positioning it with a support rod 1022. In particular embodiments, the dose distribution can be reconstructed from detected images using filtered backprojection or iterative reconstruction algorithms.

(36) Additional embodiments may comprise a circular tank filled with a scintillating liquid or circular solid scintillating embodiment of any dimension. Such a structure could have a one CCD, CMOS, light field camera or any type of photodetector or detector system capturing the light produced from the circular lateral surface of such tank or embodiment. The entire apparatus can be stationary or mounted on a motor that would rotate the entire assembly at a continuous rate or to discrete positions.

(37) All of the devices, systems and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the devices, systems and methods of this invention have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the devices, systems and/or methods in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

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