Cubic electron detector array for radiation therapy validation

Abstract

A volumetric radiation dose detector provides radiation sensors distributed along plates of a laminated stack, the stack comprising materials having different Compton scattering such that the stack has water equivalence. The plate configuration allows for convenient adjustment of the spacing between photodetectors to provide different resolutions across the entire area and depth of the detector. Printed circuit technology may be used to produce a board holding a photodetector for simplified signal management.

Description

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] --

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims the benefit of U.S. Provisional Application No. 63 / 484,582, filed February 13, 2023, and which is incorporated herein by reference. Background Art

[0005] The present invention relates generally to radiation therapy equipment and, in particular, to dosimeters for use in quality assessment of radiation therapy equipment and patient treatment plans.

[0006] Before entering clinical service, new radiotherapy linear accelerators (linacs) must undergo extensive data acquisition measurements to determine the linac's dosimetric performance. This sets the benchmark for subsequent quality assurance (QA) checks throughout the linac's lifespan. Furthermore, the acquired data serves as input to the treatment planning software (TPS), which provides accurate simulations and dose calculations for patient radiotherapy treatments to be delivered with the linac. This extensive data acquisition process is known as commissioning.

[0007] The commissioning data includes: percentage depth dose (PDD), tissue maximum ratio (TMR), beam profile, output factor, off-axis factor, wedge factor and taper factor, which are acquired for different field sizes, photon energies and electron energies.

[0008] Currently, commissioning data is measured in a water tank using an ion chamber (IC) or diode detector mounted on a carriage system to measure the water along a 50×50×50 cm 3 The slide moves along the transverse, longitudinal, and vertical axes of the volume. Beam profiles are acquired by transverse / longitudinal beam scanning, while PDD / TMR is acquired by vertical scanning. The slide is computer-controlled, and the computer software provides the acquired data in real time. Furthermore, the software can be programmed to perform multiple sequential scans according to pre-defined parameters.

[0009] A linear accelerator producing 6mV, 10mV, 15mV, 6FFF MV, and 10FFF MV photon beams, and 6MeV, 9MeV, 12MeV, 15MeV, 18MeV, and 22MeV electron beams, might require a total of 2,255 commissioning measurements. Although the water scanning system used to acquire commissioning data has been automated, it is estimated that acquiring this data might still require two to three weeks of around-the-clock operation, assuming no equipment failures. On average, data collection time might approach one month, with 10 to 12 hours of work per day, six or seven days a week. Summary of the Invention

[0010] The present invention provides a solid-state dose verification instrument that can replace water tank measurements, providing nearly instantaneous PDD, profile, and output factor data acquisition across the entire volume of interest. Solid-state detectors are embedded in water-equivalent material at fixed depths and at varying spacings to achieve a balance between detector complexity, resolution, and specific regions of interest. Deviations from the water-equivalent performance of the detectors, detector support structures, and extensive wiring are minimized by using integrated circuit technology to reduce component and conductor size and by compensating for these deviations through a calibration process that models the structure of the instrument's various materials.

[0011] More specifically, in one embodiment, the present invention provides a radiation therapy dose verification apparatus comprising a radiolucent stack of planar plates assembled together along an axis to define a measurement volume defined by the area of ​​the plates and the cumulative thickness of the plates in the stack. A plurality of solid-state electronic radiation detectors are distributed within the measurement volume and supported on the set of plates, the plates being selected to provide a radiolucent stack having water-equivalent absorption at megavoltage x-rays.

[0012] It is therefore a feature of at least one embodiment of the invention to provide an apparatus that allows rapid radiotherapy verification in a volume using a dense array of solid-state detectors.

[0013] The plates may include a first set of plates holding solid state electronic radiation detectors, the first set of plates separated by a second set of plates of a different material having lower Compton scattering at megavolt radiation levels than the material of the first set of plates.

[0014] Thus, a feature of at least one embodiment of the invention is to allow some of the plates to be customized for use in supporting circuitry for solid-state detectors (e.g., circuitry that may require materials with higher Compton scattering properties) while maintaining water equivalence by appropriate selection of the remaining plates.

[0015] In one example, the first set of boards is a printed circuit board supporting a photodetector electrically connected to an applied copper conductor having a thickness measured along an axis of less than 0.5 mm.

[0016] It is thus a feature of at least one embodiment of the present invention to enable tractable interconnection of electronic photodetection elements using axially thin, high-density copper via integrated circuit technology, avoiding the manufacturing problems associated with relatively thin discrete wiring.

[0017] The plurality of solid-state electron radiation detectors have spacing along the axis that increases from an upper side of the volume to a lower side of the volume along the axis.

[0018] It is thus a feature of at least one embodiment of the invention to provide a dose verification instrument that is well suited for use with photon and electron beams having relatively shallow penetration as well as x-ray radiation operating at greater depths.

[0019] In some embodiments, the plurality of solid-state electronic radiation detectors on each panel may be spaced closer together near a central region of the panel than at the edges of each panel.

[0020] It is thus a feature of at least one embodiment of the invention to provide improved resolution in a region that may be aligned with a treatment region of interest and a reference field size for beam dose calibration.

[0021] The solid state electronic radiation detectors may be staggered relative to a path along an axis through the stack.

[0022] It is thus a feature of at least one embodiment of the invention to minimize deviations from water equivalence caused by a relatively high density of photodetection elements by reducing the likelihood that the plurality of photodetection elements will become misaligned.

[0023] The second plate is an elastomeric material that conformally covers the first plate.

[0024] It is thus a feature of at least one embodiment of the invention to provide an instrument having inherent impact resistance and minimization of air voids.

[0025] The instrument may also include electronic circuitry that receives signals from the plurality of solid-state electronic radiation detectors and applies a calibration factor to the signals, the calibration factor being a function of the radiation energy and the radiation angle.

[0026] It is thus a feature of at least one embodiment of the invention to provide accuracy comparable to that of an ionization detector in a uniform water bath by preparing calibration weights that compensate for deviations caused by non-uniformities in the stack.

[0027] These particular objects and advantages may apply only to some embodiments falling within the claims and therefore do not limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a simplified perspective view of a radiation therapy machine that may be positioned over a detector cube of the present invention supported on a patient table and in communication with a computer for providing quality assurance reports;

[0029] Figure 2 yes Figure 1 An exploded perspective view of a cubic detector showing support for a detector array on a planar integrated circuit substrate sandwiched between water equivalent materials, the detector array having multiple regions of varying detector spacing;

[0030] Figure 3 It passes through Figure 2 A partial cross-sectional view of an assembled cubic detector illustrating different vertical spacing of the integrated circuit substrate to provide different detection resolutions at different detector depths;

[0031] Figure 4 yes Figure 3 A partial cross-sectional view of a detector showing the close fit of the water equivalent material to the detector elements and the interlacing of the detector elements;

[0032] Figure 5 is a flow chart of a calibration process for reducing the effects of non-water equivalent materials in a cube detector; and

[0033] Figure 6 is a schematic diagram showing a multiplexing system of detector elements for minimizing wire interconnections. DETAILED DESCRIPTION

[0034] Now refer to Figure 1 The radiation detector system 10 of the present invention can be used with a radiotherapy device 12 of the type that provides a radiation beam 14 that can be directed at various angles toward a patient table 16. These angles can be distributed in both azimuth and elevation around the treatment area occupied by the radiation detector system 10, and the radiation can be photon radiation or electron radiation. In this regard, the present invention contemplates use with radiotherapy linear accelerators and intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment modalities.

[0035] In one embodiment, the detector system 10 can be placed on a patient table that supports it, stabilized by its own weight and, for example, resilient feet (not shown), and positioned relative to a known reference of the radiation therapy device 12. With this positioning, the radiation detector system 10 can communicate with a computer 28 via a cable 26 or wirelessly, and the computer 28 can receive electrical signals from the detector system 10 that are indicative of the radiation dose at various locations within the measurement volume of the detector system 10. Using this data, the computer 28 can provide a display of various forms of dose information, as will be described below.

[0036] Now also refer to Figure 2 , the detector system 10 can be constructed from alternating layers of a water-equivalent material 30 (e.g., silicone rubber, acrylic, or other known water-equivalent materials) and a detector array 32 (e.g., a thin, planar substrate that supports the electronic components and the conductive traces that hold the components together). For example, the detector array 32 can employ substrates using bakelite, a plastic made from a synthetic material and having a density comparable to water, e.g., having a thickness of 1.57 mm or less or in a range between 0.78 mm and 2.36 mm. These substrates can support thin copper traces 34, e.g., less than 0.150 mm thick, that interconnect the electronic components of the detection pixel elements 36, thereby providing a point measurement of the radiation dose. In addition, the pixel elements (diodes, capacitors, MOSFETs [transistors]) can be made of graphene, which has a biological composition comparable to that of the human body and further reduces calibration factor corrections.

[0037] Typically, the water equivalence of a material can be assessed by comparing ionization chamber measurements of the material to water in terms of equivalent physical depth, percent depth dose (PDD), etc., where the water-equivalent material deviates from water in these measurements by less than 5% and typically less than 2%.

[0038] In one embodiment, the detector system 10 may have outer dimensions of 40 cm wide by 40 cm long by 35 cm high, with twenty 30 by 30 cm detector arrays 32, each providing 1200 spaced-apart pixel elements 36 along its surface.

[0039] The central region 38 of the detector array 32 may have closer spacing of the detector pixel elements 36 than the peripheral regions 40 of the detector array 32. Thus, for example, a 10 x 10 cm 2The pixel elements 36 in the central region 38 may have a spacing of 0.5 cm in both the width and length dimensions, while elsewhere the pixel elements 36 may have a spacing of 1.0 cm. The entire detector system 10 may have a total of 24,000 pixel elements 36 .

[0040] The layers of water equivalent material 30 may each be, for example, approximately 40 x 40 centimeters on a side and 1 cm thick.

[0041] Now refer to Figure 3 In one embodiment, the spacing between the detector arrays 32 can vary with height and be positioned at depths of 1.0 cm, 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm, 4.0 cm, 6.0 cm, 8.0 cm, 9.0 cm, 9.5 cm, 10.0 cm, 10.5 cm, 11.0 cm, 12.0 cm, 14.0 cm, 18.0 cm, 22.0 cm, 26.0 cm, and 30.0 cm. Thus, in a first range 31 between a depth of 1.0 cm and 4.0 cm, the spacing between the detector arrays 32 is 0.5 cm, which covers the maximum depth of the photon and electron beam dose. Furthermore, in a second range 33 between a depth of 9.0 cm and 11.0 cm, the detector arrays 32 have a spacing of 0.5 cm. This is related to the photon beam quality at a reference depth of 10 cm.

[0042] The inventors contemplate that, in one embodiment, individual or grouped detector arrays 32 supported by one or more layers of water-equivalent material 30 can be physically disassembled for isolated use. For example, the bottommost detector array 32 can be used solely for daily linear accelerator quality assurance. The upper detector layer 32 and water-equivalent material 30 within a 10 cm depth can be used solely for quality assurance of clinical programs. Figure 3 All detector arrays 32 depicted in the drawings and the assembled water equivalent material 30 are available for monthly quality assurance. These individually removable elements may be held in place by the weight of the elements in the stack, for example, when aligned by radiolucent alignment pins or the like, or may be assembled by radiolucent straps or other known attachment mechanisms.

[0043] Reference Figure 4 , the pixel elements 36 on each detector array 32 can be staggered vertically to reduce the cumulative scattering or absorption of the x-ray beam 14 received along a single trajectory that is different from the water-equivalent material 30. Typically, the water-equivalent material 30 can be configured to flow around the electronic components of the pixel elements 36 during manufacturing to provide a conformal coating to eliminate air pockets or voids that may also cause discontinuities in the water equivalence of the detector system 10. After this flow, the material can be hardened to facilitate transportation and shock resistance of the device 10, especially when the water-equivalent material 30 is an elastomer.

[0044] Now refer to Figure 5 Deviations from uniform water equivalence of the detector system 10 caused by the material of the detector array 32 can be adjusted through a calibration process in which the physical characteristics of the detector system 10 are modeled, such as the dimensions and sizes of each of the components of the detector array 32, the circuitry of the pixel elements 36, the traces 34, and the water equivalent material 30. Monte Carlo simulations of the water equivalent and detector array materials can be performed according to process block 42 for various angles and energies of photon and electron radiation to calculate the expected relative dose value at each pixel element 36, as each pixel may have manufacturing variations and respond differently to a particular beam quality. Then, at process block 44, another Monte Carlo simulation of the position of the pixel element 36 in water can be performed for each of these photon and electron energies and angles, and a weighting factor can be calculated for each of the pixel elements 36, photon and electron energies, and angles, and stored as calibration factors 46 associated with each detector system 10.

[0045] In one embodiment, Monte Carlo simulations are used (with each detector array embedded in an acrylic block and silicone rubber) to obtain a characterization function for each pixel in the array. Subsequently, using the MC data in water, a correction factor for that medium is determined for each pixel. These data can be converted to absolute dose using dose measurement data collected using a calibrated Farmer chamber.

[0046] During use of the detector system 10, as indicated at process block 48, readings from the pixel elements 36 obtained from the radiation therapy machine 12 may be adjusted by the weighting or calibration factors stored at process block 46, according to process block 49, to provide a final output 50 that has been corrected for minor deviations caused by the non-aqueous equivalence of the materials of the substrate of the detector array 32, the electronic components of the pixel elements 36, and the traces 34. The specific weighting factors may be identified by a user input indicating the radiation intensity and angle of the radiation therapy machine 12 being tested, so that the correct weighting factors may be identified from a table.

[0047] Now refer to it again Figure 1 The electrical signals from the traces 34 can be collected and digitized by the interface circuit 64 for transmission along the cable 26 to the computer 28 (in Figure 1 ), at computer 28, processing steps 49 and 50 may be implemented using the values ​​of the weighting factors stored at processing block 46.

[0048] The data collected by the present invention can be used to provide various output displays directly on the computer 28, including, for example: percent depth dose (PDD), tissue maximum ratio (TMR), beam profile, output factor, off-axis factor, wedge factor, and cone factor obtained for different field sizes, photon energies, and electron energies.

[0049] Now refer to Figure 5 , the pixel (composed of diodes, capacitors, MOSFET [transistors]) elements 36 can be arranged to be multiplexed in an active array to reduce the number of traces required to connect each of these detectors to the computer 28. In each pixel element 36, a gate line 74 can be connected to the gate of a thin film transistor 78. Transistor 78 can connect the output line 76 of the diode 36 to the anode of a capacitor 80 that stores radiation sensitivity in the form of charge. Each capacitor is discharged by disconnecting the transistor gate. In one embodiment, the diode 80 can be a PIN photodiode. The cathode of the diode 80 can be connected to a ground line (not shown) that passes through each pixel element 36 in a raster manner through the rows 70 and columns 72. The MOSFET transistor 82 shunts the pixel capacitor 80, sends the charge of the pixel capacitor 80 to the data acquisition unit (DAQ), resets the pixel capacitor 80 to zero charge, and prepares the pixel capacitor 80 for the next data acquisition 36. The diodes 80 can each have a width of approximately 0.5×0.5 cm in the plane of the pixel element 36. 2 and has a thickness along the surface normal of approximately 0.3 mm.

[0050] To further illustrate, each pixel can be composed of a diode, a capacitor, and a MOSFET. When the diode is illuminated, the MOSFET is in the off state, allowing charge to be stored in the capacitor. The MOSFET then closes the gate and opens the readout gate, which discharges the capacitor back to zero charge and prepares it for the next acquisition.

[0051] Since each detector array is an active matrix, all detectors in a row are read sequentially in a raster manner, and the number of readout channels is equal to the number of rows.

[0052] To query the dose received by diode 80 at a given pixel element 36 (time-integrated in capacitor 82), the corresponding gate line 74 is raised by the output of first multiplexer 55 of interface circuit 54 (multiplexed between gate lines 74). Output line 76 of pixel element 36 from pixel element 68 is read by second multiplexer 57 and provided to analog-to-digital converter 52 and received by cable 26 for transmission to computer 28. This process can be repeated for other pixel elements 36, for example, by similar circuits in parallel.

[0053] Data is received at the computer 28 via the interface circuit 64 and processed by one or more processors 90 which execute a stored program 92 in the computer memory 94 to provide output data on an associated terminal screen 100 (e.g., as selected by a user via a keyboard 102).

[0054] As used herein, the term "cube" is intended to describe a volumetric parallelepiped shape and is not necessarily limited to an equilateral cube.

[0055] Certain terms used herein are for reference purposes only and, therefore, are not intended to be limiting. For example, terms such as "upper," "lower," "above," and "below" refer to directions in the accompanying drawings to which they are referenced. Terms such as "front," "rear," "back," "bottom," and "side" describe the orientation of portions of a component within a consistent but arbitrary reference frame, which orientation becomes apparent by reference to the text and associated drawings describing the component in question. Such terms may include the words specifically mentioned above, derivatives thereof, and words of similar meaning. Similarly, the terms "first," "second," and other such numerical terms referring to structures do not imply a sequence or order unless the context clearly indicates otherwise.

[0056] When introducing the elements or features of the present disclosure and exemplary embodiments, the quantifier-free modifiers, "the" and "said" are intended to mean that there are one or more such elements or features. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be other elements or features except those specifically pointed out. It should also be understood that the method steps, processing and operations described herein are not to be interpreted as necessarily requiring them to be performed in the particular order discussed or illustrated, unless clearly identified as an execution order. It should also be understood that additional or alternative steps can be adopted.

[0057] References to "microprocessor" and "processor" or "the microprocessor" and "the processor" may be understood to include one or more microprocessors that may communicate in one or more independent and / or distributed environments, and thus may be configured to communicate with other processors via wired or wireless communications, wherein such one or more processors may be configured to operate on one or more processor-controlled devices, which may be similar or different devices. Furthermore, unless otherwise specified, references to memory may include one or more processor-readable and accessible memory elements and / or components, which may be internal to the processor-controlled device, external to the processor-controlled device, and accessible via a wired or wireless network.

[0058] In particular, the present invention is not intended to be limited to the embodiments and illustrations contained herein, and the claims should be understood to include modifications of these embodiments, including portions of the embodiments and combinations of elements of different embodiments within the scope of the appended claims. All disclosures described herein, including patent disclosures and non-patent disclosures, are hereby incorporated by reference in their entirety.

[0059] To assist the Patent Office and any reader of any patent that issues based on this application in interpreting the appended claims, Applicant wishes to point out that unless the words "means for" or "step for" are expressly used in a particular claim, Applicant does not intend that any appended claim or claim element invoke 35 U.S.C. §112(f).

Claims

1. A radiotherapy dose verification instrument, comprising: a radiolucent stack of planar plates assembled together along an axis to define a measurement volume defined by the areas of said plates and the cumulative thickness of said plates in said stack; as well as a plurality of solid-state electron radiation detectors, distributed in the measurement volume and supported on a set of the plates; The ray-transmissive stack provides water-equivalent absorption at megavoltage x-rays.

2. The radiotherapy dose verification instrument according to claim 1, wherein: The plates include a first set of plates holding the solid-state electronic radiation detector, the first set of plates being separated by a second set of plates of a different material having lower Compton scattering at megavolt radiation levels than the material of the first set of plates.

3. The radiotherapy dose verification instrument according to claim 2, wherein: The second set of plates is selected from a material selected from the group consisting of silicone rubber and acrylic.

4. The radiotherapy dose verification instrument according to claim 2, wherein: The first set of boards is a printed circuit board supporting applied copper conductors having a thickness measured along the axis of less than 0.5 mm.

5. The radiotherapy dose verification instrument according to claim 4, wherein: The first set of plates is selected from materials including glass reinforced epoxy and glass reinforced polytetrafluoroethylene.

6. The radiotherapy dose verification instrument according to claim 1, wherein: The spacing of the plurality of solid-state electron radiation detectors along the axis increases along the axis from an upper side of the volume to a lower side of the volume.

7. The radiotherapy dose verification instrument according to claim 1, wherein: The plurality of solid-state electronic radiation detectors on each panel are spaced closer together near a central region of the panel than at an edge of each panel.

8. The radiotherapy dose verification instrument according to claim 1, wherein: The number of solid-state electron radiating elements exceeds 20,000.

9. The radiotherapy dose verification instrument according to claim 1, wherein: The solid state electronic radiation detectors are staggered relative to a path along the axis through the stack.

10. The radiotherapy dose verification instrument according to claim 1, wherein: The second plate is an elastomeric material conformally covering the first plate.

11. The radiotherapy dose verification instrument according to claim 1, wherein: The stack has no air gaps between the plates.

12. The radiation therapy dose verification instrument of claim 1 , further comprising an electronic circuit that receives signals from the plurality of solid-state electronic radiation detectors and applies a calibration factor to the signals, the calibration factor being a function of radiation energy and radiation angle.

13. The radiotherapy dose verification instrument according to claim 1, wherein: The radiolucent stack of planar plates is releasably assembled along the axis to allow subsets of the solid-state electronic radiation detectors supported on subsets of the plates to be independently positioned for use in a radiation beam.

14. The radiotherapy dose verification instrument according to claim 13, wherein: A single lowest planar panel is releasably detachable from the stack for individual use.

15. The radiotherapy dose verification instrument according to claim 13, wherein: An upper set of planar panels comprising a plurality of planar panels is releasably detachable from the stack for individual use.

16. The radiotherapy dose verification instrument according to claim 1, wherein: The plurality of solid-state electron radiation detectors are composed of graphene.

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