Ionizing-Radiation Beam Monitoring System
A transmissive ionizing-radiation beam monitoring system includes an enclosure structure including an entrance window and an exit window to an incident ionizing-radiation beam, where the entrance window and the exit window are highly transmissive. The system further includes a thin scintillator within the enclosure structure that is directly in an incident ionizing-radiation beam path and transmissive to the incident radiation beam and an ultraviolet (“UV”) illumination source within the enclosure structure facing the scintillator for internal system calibration. Embodiments further include a UV photosensor within the enclosure structure positioned to monitor and calibrate the UV illumination source and a machine vision camera within the enclosure structure that includes a lens which views the scintillator through a close proximity mirror including a folded optical axis system located to a side of the scintillator.
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This application is a continuation of U.S. patent application Ser. No. 16/529,200, filed on Aug. 1, 2019, which claims priority to U.S. Provisional Pat. Appln. Ser. No. 62/714,937, filed on Aug. 6, 2018, to U.S. Provisional Pat. Appln. Ser. No. 62/815,006, filed on Mar. 7, 2019, and to U.S. Provisional Pat. Appln. Ser. No. 62/859,952, filed on Jun. 11, 2019. The disclosure of each of these applications is hereby incorporated by reference.
GOVERNMENT LICENSE RIGHTSThe invention was made in part with government support under one SBIR (Small Business Innovation Research) Grant (Number: 5R44CA183437) awarded to Integrated Sensors, LLC by the National Institutes of Health (National Cancer Institute), and two SBIR Assistance Agreements (Award Nos. DE-SC0013292 and DE-SC0019597) awarded to Integrated Sensors, LLC by the U.S. Department of Energy (Office of Science). The government has certain rights in the invention.
FIELDOne embodiment is directed generally to radiation beam monitoring, and in particular to monitoring ionizing beams of particle or photon radiation while having minimal impact on the quality of the radiation beam itself.
BACKGROUND INFORMATIONThe most common type of radiation therapy for the treatment of cancer is external beam radiation therapy (“EBRT”). For this treatment, an accelerator is used to generate and precisely deliver relatively high-energy particle or photon beams from outside the body into the tumor. There are a variety of EBRT technologies, with the type of radiation used falling into two general categories: (1) ionizing particles such as protons, ions, electrons, etc., and (2) ionizing photons such as relatively low-MeV gamma rays or X-rays. Ionizing photons are the more common type of radiation employed for EBRT. For particle beam radiation therapy, in addition to protons, carbon ions and electrons, other types of particle beams used or being investigated include helium, oxygen, neon and argon ions, as well as low-energy neutrons (e.g., slow to thermal neutrons). Low-energy neutrons are used, for example, in boron neutron capture therapy (“BNCT”) and gadolinium neutron capture therapy (“Gd-NCT”).
For both particle and photon EBRT, there are a variety of delivery methods, including intensity modulated radiation therapy (“IMRT”), intensity modulated proton therapy (“IMPT”), three-dimensional conformal radiation therapy (“3D-CRT”), image guided radiation therapy (“IGRT”), volumetric modulated arc therapy (“VMAT”), pencil-beam spot scanning, pencil-beam raster scanning, helical-tomotherapy, stereotactic radiosurgery (“SRS”), stereotactic body radiation therapy (“SBRT”), fractionated stereotactic radiotherapy (“FSRT”), spatially fractionated grid radiation therapy (“SFGRT”), ultrahigh dose-rate flash therapy (“FLASH”), intraoperative radiation therapy (“IORT”), boron neutron capture therapy (“BNCT”), gadolinium neutron capture therapy (“Gd-NCT”), etc.
SUMMARYOne embodiment is a transmissive ionizing-radiation beam monitoring system that includes an enclosure structure including an entrance window and an exit window to an incident ionizing-radiation beam, where the entrance window and the exit window are highly transmissive. The system further includes a thin scintillator within the enclosure structure that is directly in an incident ionizing-radiation beam path and transmissive to the incident radiation beam and an ultraviolet (“UV”) illumination source within the enclosure structure facing the scintillator for internal system calibration. Embodiments further include a UV photosensor within the enclosure structure positioned to monitor and calibrate the UV illumination source and a machine vision camera within the enclosure structure that includes a lens which views the scintillator through a close proximity mirror including a folded optical axis system located to a side of the scintillator.
Embodiments are directed generally to ultra-fast transmissive (“UFT”) two-dimensional (“2D”), high resolution, ionizing particle and photon beam monitors primarily for applications based on, or related to, external beam radiation therapy (“EBRT”), including the monitoring in “real-time” of beam position and movement, intensity profile including tail, beam fluence/external dosimetry, angular divergence and patient treatment quality assurance.
In embodiments of the present disclosure, the term “ultra-fast” refers to “real-time” on-line monitoring and data analysis of streaming images of an ionizing-radiation beam within approximately 10 ms or less per image, corresponding to a data analysis rate of approximately 100 frames per second (“fps”) or faster. For some embodiments, the streaming images can be coming in at rates of 1,000 to 10,000 fps (i.e., 1 ms to 0.1 ms) with the data analysis occurring concurrently. Further, the terms “transmissive” and “highly transmissive” are adjectives used to describe the relatively small amount of energy that a particle or photon loses in transit through a given material or system, which will be different for an entrance or exit window as compared to the scintillator material itself as compared to the integrated beam monitor system comprising the entrance window, exit window, scintillator, and the column of air between the entrance and exit windows. For any given system the relative amount of energy loss will vary greatly at different incident particle or photon energies which can vary over many orders-of-magnitude, and for different types of particles from neutrons to protons to carbon-ions, etc. For an EBRT application such as proton therapy using a proton beam having an incident energy of 210 MeV, the term “highly transmissive” would mean losing no more than about ≤0.1%) of its incident energy in transit through the UFT beam monitor system (i.e., losing ≤0.2 MeV), but for the exact same system at 80 MeV “highly transmissive” would mean losing ≤0.5%) (i.e., losing ≤0.4 MeV). For this example at the same energies, the term “transmissive” would mean at 210 MeV losing no more than about ≤0.2%) of its incident energy in transit through the UFT beam monitor system (i.e., losing ≤0.4 MeV), but for the same system at 80 MeV the term “transmissive” would mean losing 1% (i.e., losing ≤0.8 MeV).
The beam monitors in accordance to embodiments incorporate thin and ultra-thin scintillator materials (e.g., scintillator sheet or film material) and are capable of internal, frequent, self-calibration to compensate for a variety of factors including system non-uniformity including camera sensor/pixel response, optical system distortions, slow degradation of the scintillator material due to radiation damage, signal drift due to temperature rise within the monitor enclosure, etc. In embodiments, the term “ultra-thin” refers to both window (i.e., entrance and/or exit window) and scintillator materials having a thickness of ≤0.05 mm, and the term “thin” refers to scintillator materials having a thickness of ≤0.5 mm and thus also includes ultra-thin scintillators.
The integrated detector/monitor in accordance to embodiments has an intrinsic 2D position resolution in the range of ˜0.03 mm to 0.2 mm, depending on the application specification requirements, and is highly transparent to the incident ionizing particle or photon beam, thereby resulting in minimal beam scatter, low to extremely low energy straggling, and minimal generation of secondary radiation. Embodiments, in addition to EBRT, can be used for the monitoring of low-luminosity exotic particle beams and/or high-luminosity particle beams generated by research accelerators for scientific experiments, industrial particle and photon beam monitoring for materials processing (e.g., high energy ion implantation, food and medical sterilization, cutting and welding, etc.), materials analysis, non-destructive analysis, radioisotope production, etc. Beam monitors in accordance to embodiments generally do not require a controlled atmosphere or vacuum environment for proper operation, although some embodiments have been designed for operation in vacuum or controlled gaseous environments.
Embodiments for EBRT applications generally result in positioning the beam monitor downstream from the accelerator exit nozzle in an ambient air atmosphere. However, other embodiments are configured to operate within the vacuum environment of the beamline pipe to optimize and/or monitor the beam shape, intensity, position and beam focus prior to reaching the beam exit/nozzle or target region. Embodiments for EBRT applications downstream from the nozzle incorporate a unique folded optical configuration to achieve a thin profile to minimize encroaching upon the confined and narrow space between the beam nozzle exit and the patient.
Due to the ultra-fast response capability of the embodiments of beam monitors, they can provide sub-millisecond and even microsecond beam analysis and feedback to the delivery system, thereby allowing corrective actions to be taken if necessary. For EBRT, this capability can potentially improve the treatment delivery efficacy and protect the patient, especially for recent “FLASH” therapy applications. For nuclear and high energy physics, this capability can provide particle time-of-flight (TOF) information in the range of 50 to 100 μs, or greater.
It is known to use a scintillator, including a plastic scintillator to detect ionizing radiation, coupled with an electronic photodetection device to quantitatively measure the emitted photons from the scintillator. It is also known to use a digital camera to record the light emitted from an irradiated scintillator in applications ranging from monitoring the beam shape and position of an electron beam, to using X-rays irradiating a scintillator to evaluate the quality of mechanical welds, to optimizing the beam delivery system used in proton beam therapy.
In contrast to known uses, embodiments implement multi-camera folded optical configurations, such as 2, 3, 4, 6, 8, 10, 12 cameras, for advanced beam monitoring systems that provide critical performance and space-saving advantages such as extremely high spatial resolution while minimizing encroachment on the limited space existing between the EBRT exit nozzle and the patient's body. Embodiments also include configurations of relatively compact machine vision cameras with imaging sensors that can stream images live to a computer system that includes a frame grabber for real-time data processing and analysis, the use of machine vision cameras that can be programmed for application specific parameter optimization such as selection of exposure time, gray scale level (i.e., bit depth), acquisition control and frame rate, gain control, black level control, gamma correction for pixel intensity, pixel binning, pixel sharpening, windowing down the area or region of interest to achieve higher frame rates for faster beam analysis. Embodiments further include the use of both single and double scintillator configurations that can be integrated as part of an easy to replace foil-window/scintillator module package, and rolled scintillator-film motorized spool assemblies for automated scintillator film advancement/replacement that uses novel polymer thin film scintillator materials such as biaxially-oriented polyethylene naphthalate (“BoPEN”), biaxially-oriented polyethylene terephthalate (“BoPET”), polyethersulfone (“PES”), etc. that are intrinsic scintillators without the addition of fluor dopants. Embodiments include novel designs for quick replacement of radiation damaged scintillator film or sheet with new scintillator film or sheet without significant service downtime and recalibration time associated with the scintillator replacement process, configurations for real-time beam monitoring systems operating in a vacuum environment, configurations for beam monitoring systems operating in either a naturally circulating or controlled flow-through ambient air or special gaseous environment such as an enriched oxygen gaseous atmosphere to possibly minimize radiation damage by enhancing oxygen assisted radiation damage recovery, configurations incorporating actively cooled camera sensors for enhanced performance and reduced radiation damage of the camera sensor element, configurations incorporating the addition of internal UV sources such as UV-LEDs and internal UV detectors such as UV-photodiodes and appropriate filters such as bandpass filters to achieve internal self-calibration of system non-uniformity and near continuous self-correction for progressive scintillator radiation damage; real-time software correction of optical system distortions, perspective distortions (e.g., keystoning), aberrations and non-uniformities including camera image sensor pixel defects and non-uniformity. Embodiments include configurations utilizing 3-way tees or wyes, 4-way-cross, 5-way-cross and 6-way-cross vacuum chamber configurations for beamline vacuum operation that allow the use of either two cameras, or two photomultiplier tubes (“PMT”s), or one camera and one PMT, or PMT replacements such as solid state photomultipliers (“SSPM”) including silicon photomultipliers (“SiPM”), avalanche photodiodes (“APD”), single-photon avalanche diodes (“SPAD”), etc. Embodiments include high dynamic range (“HDR”) computational imaging and with the thinnest scintillator films have extremely low beam energy straggling with minimal generation of secondary ionizing particles and photons.
Embodiments achieve advantages in part by using a scintillator film material, available in continuous rolls (e.g., >1000 ft length) of about 70 cm width and greater, and thicknesses from about 1 μm to 250 μm in conjunction with other components to achieve unexpected results with regard to radiation damage resistance, photon emission, and as a thin and/or ultra-thin film scintillator. Embodiments include designs to take advantage of the new thin and ultra-thin scintillator material which is highly resistant to radiation damage, while being able to minimize and possibly eliminate most problems having to do with scintillator non-uniformity and time consuming scintillator material replacement and system calibration.
Embodiments include an innovative folded-optics design to minimize the product profile/thickness to within about 6-14 cm, depending upon scintillator and camera size and camera angle. Embodiments include an innovative automated, internal, rapid calibration system using UV-LEDs, UV-photodiodes, and UV and VIS bandpass filters, with an estimated time for system calibration of about one minute or less. Embodiments include machine vision cameras that would typically stream images at frame rates from about 100 fps to 40,000 fps.
Embodiments discussed below include an in-line beam monitor design (e.g.
Embodiments further enhance timing resolution for TOF measurements by increasing photon collection, such as through the use of two PMTs or SSPMs in the opposite arms of a 6-way-cross instead on one PMT (or SSPM) and one camera, or improving the collection of photons from the front side of a scintillator by depositing a reflective coating on the scintillator back side, or roughening the front collection surface of a scintillator to prevent total internal reflection.
Embodiments include multi-camera configurations (e.g. 2, 3, 4, 6, 8, 10, 12, etc., cameras) with FPGA frame grabbers and software that can compile, integrate and analyze streaming images in real-time of the moving beam, while correcting for optical image perspective/keystone distortions, lens distortions, vignetting, scintillator non-uniformity, camera sensor pixel non-uniformity, defective and radiation damaged pixels, etc.
Embodiments include manual or motor controlled push-pull linear positioners and/or rotary drives to advance fresh scintillator film as needed into the incident beam active area. Embodiments include a load-lock vacuum chamber design to change scintillator films without having to break the beamline vacuum. Embodiments include an ultra-thin, light-blocking beam entrance and exit foil and/or polymer window, bonded to a thin frame, that can also be bonded to the scintillator film or sheet material to make a simple window/scintillator replaceable module package that can be dropped into a pocket in the beam monitor front and/or back cover plate and calibrated within a minute or so without having to open up the system enclosure.
Embodiments have a design based on two different in-line scintillators, one sensitive to essentially all particles and high energy photons/gammas except neutrons, and the other doped with a high neutron cross-section isotope such as B10, Li6 or Gd in order to make it neutron sensitive. By digitally subtracting the image/signal of the first scintillator from that of the second scintillator, the resulting second scintillator image/signal will be primarily that of the neutron beam and can achieve the high performance at low cost desired in a high gamma discrimination neutron detection system.
Most known EBRT particle accelerators are designed for pencil-beam spot scanning, but a few systems are designed for pencil-beam raster scanning. The beam monitor embodiments disclosed below are compatible with both types of pencil-beam scanning systems, with most configured to operate downstream from the exit nozzle, but some embodiments have been designed to operate upstream of the nozzle in the vacuum environment of the beamline delivery system either in the patient treatment room or prior to the treatment room and switch house and close to the accelerator. The purpose of such systems operating in the beamline vacuum is usually diagnostic to facilitate beam tuning including measurement and optimization of the 2D beam profile in the delivery system, whether for EBRT, or for nuclear and high energy physics. In all cases, the scintillator material should be an extremely thin film so as to be almost transparent with very little low energy straggling so as not to degrade the beam in the process of measuring it. For such applications, the scintillator film in some embodiments should be less than 100 μm thick and possibly as thin as 1 μm.
In embodiments the scintillator film BoPEN is employed in thickness down to 1 μm, and in some embodiments this film is physically attached to a rigid frame as shown in some of the 6-way-cross embodiments disclosed below.
Experimental results showed a 33.0% initial decrease in scintillator fluorescence from a 191 μm thick BoPEN film measured almost immediately after being irradiated for 5 minutes by a low energy proton beam that resulted in a film dose of 59 kGy. Specifically,
The above BoPEN film (density of 1.36 g/cc) radiation damage experiments employed a 5.4 MeV proton beam that was continuously irradiated for 300 seconds at an incident beam current density of 2.4 nA/cm2. Upon passing through the BoPEN film, each 5.4 MeV proton loses about 2.14 MeV. Given the above beam current and integrated exposure time, the BoPEN scintillator film was subjected to 59 kGy of accumulated radiation dose (1 Gy=1 J/kg) absorption as calculated below:
N=(2.4×10−9 coul/sec-cm2)*(6.25×1018 protons/coul)*(300 sec)=4.5×1012 protons/cm2
J=2.14 MeV/proton=(2.14×106 eV/proton)*(1.6×10−19 J/eV)=3.4×10−13 J/proton
Mass=(1.36 g/cm3)*(0.0191 cm)=0.026 g/cm2=2.6×10−5 kg/cm2
Dose=(3.4×10−13 J/proton)*(4.5×1012 protons/cm2)/2.6×10−5 kg/cm2=1.53J/2.6×10−5 kg=59×103 Gy
Dose rate=59 kGy/300 sec=0.20 kGy/s
For a transmissive particle beam monitor based on viewing and measuring the beam via its effect on scintillator emission, the effect of radiation damage can be quantified by equating it to the reduction in scintillator yield as measured by relative light loss (i.e., fluorescence signal reduction). With respect to obvious visual radiation damage, none of the more than 30 BoPEN samples irradiated to date, at dosage levels up to ˜60 kGy, have shown any visual signs of scintillator discoloration or surface degradation which was an unexpected result. However, BoPEN films have discolored at 400 kGy (see discussion below and Table 1).
In estimating the acceleration factor in experimental uses for different applications, with proton beam therapy being of particular interest, an average conventional daily patient treatment regime delivers ˜2 Gy per session. So, the above test that delivered 59,000 Gy to the BoPEN scintillator film in 300 seconds is presumably equivalent to the dose incurred in treating ˜30,000 patients. In other words, 1 second of accelerated irradiation in the 5.4 MeV test beam, approximately simulates the radiation received by the scintillator in conventionally treating ˜100 patients (a lesser number of patients for FLASH therapy). Or viewed another way, if a typical proton beam treatment room can process about 30 patients per day, then 5 minutes of the above accelerated proton beam test is equivalent to ˜1000 days of conventional patient treatments in a one-room facility. This degree of radiation damage resistance, with no obvious visual sign of surface degradation or discoloration in an off-the-shelf commercial polyester film, under such an aggressive, high rate, accelerated testing regime is an unexpected result.
From the BoPEN scintillator test experimental results to date, it appears that at the above dose rate of 0.2 kGy/s that radiation damage is linear with exposure, up to rates approaching 10 kGy/s (as shown in
Hence the measured rad-damage values previously stated and appearing in
As can be seen in
Initial adjustment for front surface light loss in 191 μm film=(1−0.444)117.5%)=9.7%
Additional adjustment for difference in beam current density=(1.10/1.35)*(9.7%)=7.9%
Further, in experiments there was excellent agreement from two different 191 μm thick BoPEN samples, measured more than three weeks apart, using significantly different beam currents. In particular, the initial 19.7% light loss in
In estimating the beam energy lost in transit through the film, and the beam shape and intensity via its fluorescence profile, it is necessary to know the BoPEN film thickness and uniformity. A convenient non-destructive method for measuring film thickness and uniformity is via the front/back surface reflectance generated by spectral interference. This method can accurately measure film thicknesses over the full range from ˜1 μm to 250 μm, and to within about ±0.1 μm accuracy. For the films in
The above data indicates that thinner BoPEN scintillator films appear to be more radiation damage resistant than the thicker films (e.g., see the 300 second plots for the 3, 6, 12 and 191 μm thickness BoPEN films in
In embodiments, in order to refine the above estimates for the scintillator dose exposure under more realistic clinical proton therapy conditions, an additional 20% scintillator dose can account for patient planning and calibration activity, and weekly machine maintenance. This adjustment means that the previously stated estimate of 30 patients per day, at 2 Gy per patient, corresponding to 60 Gy per day scintillator dosage, might prudently be increased by about 20% to 72 Gy per day. Therefore, the above calculated 59 kGy of accelerated exposure at a test facility, would be equivalent to 819 days of accumulated patient service assuming conventional irradiation treatment (i.e., not FLASH).
If a proton beam facility operates 5 days per week, then 819 days of service corresponds to 164 weeks which would be more than 3.1 years of continuous service. Assuming a linear radiation damage model (e.g., shown in
However, it appears that in the range of accelerated radiation dose rates chosen for modeling the performance of both therapeutic particle beams and for nuclear physics particle beam monitors (i.e., dose rates of 9 kGy/s shown in Table 1), projections based on a linear model should provide a good estimate of scintillator performance and any corrections for exponential behavior would be minor as shown in
None of the BoPEN films receiving dosages up to 59 kGy (i.e., 300 seconds with 5.4 MeV proton beam at a current density of 2.4 nA/cm2) and at a dose rate of 0.20 kGy/sec showed any sign of surface degradation or discoloration despite significant decreases in fluorescence due to rad-damage as shown in
Rad-damage induced darkening (i.e. yellow-brown discoloration) has been observed in a 191 μm thick BoPEN film using the 5.4 MeV proton beam at a 10 nA current, with a fixed, non-rastered beam focused on a 0.25 cm2 area for 118 seconds. The resulting current density of 40 nA/cm2 yielded a dose rate of 3.3 kGy/s and produced an accumulated dose of 390 kGy. This dose rate was 16 times greater than received by the 59 kGy dose irradiated sample disclosed above. However, when the 390 kGy dose film was viewed two months later, it was discovered that the darkened/discoloration area had completely disappeared, so apparently at least some visually damaged BoPEN films can self-heal/recover in air to the extent that they no longer appear visually discolored.
In order to evaluate the dosage associated with irreversible physical damage (such as burning a hole into the film by proton ablation), a more stable fixed proton beam accelerator was used with a 191 μm thick BoPEN film at a reduced proton kinetic energy of 3.0 MeV and with a much tighter beam focus over an ablated hole area of 0.020 cm2 (i.e., diameter at hole surface was 1.6 mm as disclosed below), at beam currents of 1 nA for 53 seconds, 10 nA for 66 seconds, and 50 nA for 33 seconds. At each beam current a series of images were recorded at a shutter time/exposure of 1 ms, and at a frame rate of 2 fps for all three cases.
The number of images recorded for the above experiment corresponded to 89 images at 1 nA (see disclosure below), 133 images at 10 nA, and 67 images at 50 nA, with the fluorescence pattern and signal intensity recorded for each picture on a pixel-by-pixel basis as seen in
As previously disclosed, the fluorescence decrease followed close to a linear fit as seen by the solid line in
In contrast to the 1 nA fixed beam at 3 MeV, the subsequent 10 nA fixed beam suffered more than an order-of-magnitude larger, 18% decrease in its overall fluorescence in its first second of irradiation as compared to its initial signal, which must be due to immediate surface ablation. Similarly the 50 nA fixed beam suffered a 43% decrease in its overall fluorescence in its first second of irradiation as compared to its initial signal as seen in
As disclosed above, the very “first” digital image (1 ms shutter speed) taken within the 1st second of irradiation (i.e., at 2 fps and prior to significant ablation) at a beam current of 10 nA appears in
As disclosed above, an incident 5.4 MeV proton beam has adequate energy to pass through the 191 μm thick BoPEN film and exit with a residual energy of 3.26 MeV. However, at 3.0 MeV the proton beam only penetrates approximately 119 μm into the 191 μm thick BoPEN film. If the proton beam current density is sufficient to cause ablation and start “burning a hole” in the BoPEN film, then as the ablation proceeds the beam will penetrate further and further into the film, eventually exiting first at reduced energy and then almost at full energy once the hole has burrowed or punched through. Examination under a microscope confirmed that even at the 50 nA beam current, the ablated hole did not go all the way through the 191 μm thick film during the 33 seconds of beam irradiation, which followed the prior 66 seconds of much slower ablation at 10 nA.
The total estimated beam penetration depth was about 150-160 μm, and encompassed a maximum surface ablation area of ˜0.020 cm2, although the hole ellipsoid minor and major axes in the area of deepest penetration at the hole bottom was measured to be much smaller at about 0.4×0.6 mm (0.002 cm2). Based on the ablated hole area surface dimensions, the associated beam current density was 2500 nA/cm2 at 50 nA, corresponding to an accumulated dose of 15 MGy at a dose rate of 460 kGy/sec (see Table 1). At this dose rate, it is clear from the “average pixel signal” in
The ablated area/hole created by the 50 nA beam was elliptically shaped with measured minor and major axes of ˜1.4 mm×1.8 mm, corresponding to an equivalent circle with a radius of 0.80 mm and an area of 2.0 mm2. However the Gaussian fit distribution for
The maximum beam current and minimum beam radius in the vacuum beamline pipe of a 250 MeV proton accelerator is typically ˜800 nA for a superconducting cyclotron with approximately a 1 mm beam radius. The associated beam current density is ˜25,000 nA/cm2. Under such conditions with a 25-50 μm thick BoPEN film scintillator, the dose rate could be 100-200 kGy/s, causing significant ablation of the BoPEN film and resulting in hole-burning within a minute or so. Good practice would dictate that the film radiation exposure in any one spot be limited to ten seconds or less.
For the above case of a 100-200 kGy/s dose rate, embodiments include a 5-way or 6-way-cross vacuum chamber that is designed to allow the BoPEN scintillator to be moved out of the beam within seconds after being moved into the beam to capture the required beam images. The proton beam image in
The low-energy proton beam tests at 3.0 MeV and 5.4 MeV for the 191 μm thick BoPEN film scintillator as summarized in Table 1 above covered a matrix spanning roughly three (3) orders-of-magnitude for the critical parameters of beam current density, absorbed dose and dose rate. The results of the described accelerated test program demonstrate the exceptional performance to be realized from the broad family of disclosed embodiments that have led to a wide variety of UFT (ultra-fast transmissive) high-resolution detection system embodiments for real-time monitoring of ionizing particle and photon beams. The targeted applications for the described embodiments below, include not only proton therapy, but all other types of particle and photon external beam radiation therapy (“EBRT”), as well as beam monitors for industrial and research accelerators including those used in nuclear and high energy physics, etc.
With regard to proton therapy, embodiments demonstrate an unexpected result that 5 minutes of testing at a beam particle energy of 5.4 MeV, a beam current density of 2.4 nA/cm2, and an irradiation dose rate of 200 Gy/s will not cause visual damage to the BoPEN scintillator, but would be roughly equivalent to the dose incurred in treating ˜30,000 patients assuming a conventional dose of 2 Gy per patient, or 3,000 patients at a FLASH dose of 20 Gy per patient. Thus radiation damage to a BoPEN film scintillator is not a significant issue and can be readily handled as disclosed below.
Given the previous estimate of 0.04% to 0.07% maximum accumulated scintillator radiation damage per week in a “typical” treatment room facility seeing 30 patients per day, embodiments have a need to advance a fresh area of scintillator film to the scintillator isocenter on a bi-weekly, monthly or possibly even quarterly basis; the latter period corresponding to a maximum estimated fluorescence loss of ˜0.9%. Therefore, as a practical matter it appears that having to measure the daily or weekly rad-damage contribution to scintillator non-uniformity can likely be ignored due to it being inconsequential, which has important implications. Specifically, calibration efforts in embodiments can be shifted to measuring and quantifying the other parameters that have to be monitored for achieving and maintaining an integrated system accuracy of 1% or better on a per patient daily basis. It follows that given the very small amount of rad-damage incurring on a weekly basis, a strategy of advancing the scintillator film, either by unwinding it from a spool (e.g., similar to advancing 35 mm film frame-by-frame in a camera) or by pushing a frame with the film mounted to it by a few centimeters on a periodic basis (e.g. weekly, biweekly, monthly, etc.) could be implemented via a variety of embodiments as disclosed below.
System 800 includes a two mirror 830, folded optical configuration which minimizes the light-tight enclosure depth/thickness while incorporating a mechanism for advancing the scintillator film 860 to minimize or eliminate having to correct for scintillator radiation damage. A relatively thick scintillator film such as 125-250 μm thick BoPEN film (i.e., 5-10 mils) is wound onto a small diameter (e.g., 2.5″) feeder spool 870 to an outer diameter (“OD”) that fits within the light-tight enclosure (e.g., ˜4″). This film could be of any width (e.g., 25-45 cm), and could contain a total length of about 20-25 meters of 191 μm BoPEN scintillator. In this embodiment, film 860 would be pulled across an active window area 812 onto a suitable take-up spool 872, and advanced by a stepper motor 880 that rotates the take-up spool spindle as required. An ultra-thin dark colored exit window 814, such as 15 to 25 μm thick black aluminum foil, is shown in
In connection with the film rolls used in some embodiments, much longer rolls of the thickness and width disclosed above have been used for decades in aerial photography and advanced by motor drives at high speed—e.g., Kodak Aerial Ektacolor Print Film (SO-149) which with its color emulsion and gel backing has a total thickness of 213 μm. It is noted that standard 35 mm and 70 mm wide, motion picture film is typically advanced at 24 fps for “normal” motion but faster for slow motion, and some 70 mm IMAX films have been run at 48 fps (i.e., 200 meters/minute). If, for example, the BoPEN film were advanced 5 cm on a biweekly basis to shift the most likely rad-damaged scintillator center area (i.e., isocenter region) midway to the side, then the previously described 20-25 meter film length could last approximately 16 years. If the same BoPEN film were advanced 10 or 20 cm biweekly, then a single roll would last either 8 or 4 years respectively before requiring replacement.
Aerial films were previously made in four standard widths, 35 mm, 70 mm, 126 mm and 240 mm. These widths are the edge-to-edge dimensions and include sprockets on both sides, so for example the maximum image width on the 70 mm film is ˜58 mm, and on the 240 mm is 228 mm. The thinnest Kodak aerial film Estar “Ultra-Thin” Base made was 30 μm (i.e., 0.0012″) but was still strong enough to hold sprocket holes without tearing. However the standard Kodak Estar Ultra-Thin Base was 38 μm (i.e., 0.0015″), while the standard Kodak Estar Thick Base was 178 μm (i.e., 0.0070″). Film roll lengths for the Thick Estar Bases went from 100 to 800 feet, whereas film roll lengths of up to 2000 feet were standard for the other thinner Estar base films. A detailed thickness study by Kodak for their standard 240 mm wide Estar Base in a standard 30 meter length film roll yielded that “the thickness variation across essentially the entire roll length had a standard deviation of less than 1.85 μm”. However, within the 23 cm×23 cm aerial format picture area (i.e., 9″×9″) the standard thickness deviation was 1.0 μm. For Kodak 70 mm wide films, the spool core diameter was 31/32″ for film roll lengths up to 200 feet for the Estar Thin Base (64 μm), 150 feet for the standard Estar Base (102 μm), and 100 feet for the Estar Thick Base (i.e. 178 μm without emulsion and 184 μm thickness for B/W emulsions and 213 μm for their thickest color film). For longer rolls of 70 mm wide film, and for all lengths of 126 mm and 240 mm width film rolls, a spool core diameter of 2.125″ was used for all Estar film base thicknesses. Thus the suggested spool core diameter of 2.5″ disclosed above, and film length of 20-25 meters, are conservative given the standard specifications used for aerial films, as is the film thickness uniformity across the active area.
For the multi-arm cross, roll film embodiments, the 25 μm thick BoPEN should be ideal, especially considering that the BoPEN film is stronger than the Estar Base film (i.e., BoPET) used by Kodak, and the sprocket film holes that can tear in rapid advance photographic film systems are not required for the much slower advancing roll-to-roll embodiments described herein. In addition, the 12 μm thick BoPEN is also a potentially viable thickness for the roll-to-roll scintillator film designs such as the highly transmissive beamline vacuum cross monitors shown in
For embodiments that do not require roll-to-roll film advance systems, a variety of simpler yet more versatile transmissive beam monitor embodiments have been designed for fast exchange of different scintillator materials optimized for a wide variety of ionizing particles and energies including photons and neutrons in a wide range of film and sheet thicknesses (e.g., from ˜1 μm to ≥1 mm). For those monitors designed for beamline applications, both single-frame and double-frame, multi-arm cross structures are disclosed in which the scintillator is mounted to a stiff frame in contact with a push-pull mechanism as shown for three different 6-way-cross embodiments in
All of the embodiments disclosed herein with associated figures/drawings incorporate the previously described system/hardware required for internal calibration and beam image analysis. The calibration system and its operation can be initiated either manually or automatically (e.g., on a pre-programmed schedule) and is based on activating an internal UV-LED source or sources to illuminate the scintillator film for a short time (e.g., seconds) and capturing images of the fluorescence intensity pattern and comparing them to previous images by means of an appropriate computer system to detect any changes in the system response, including changes in the scintillator fluorescence or camera sensor such as might be caused by radiation damage, etc. In order to monitor the stability of the UV-source, each UV-LED is itself monitored by a dedicated proximity UV-photosensor such as a photodiode to correct for any source intensity change or drift over time. The computer system in one embodiment is a dedicated, low-latency, fast-PC (personal computer) or workstation, etc., having a processor that executes instructions. In other embodiments, the computer system is a customized FPGA based PCB (printed circuit board) or frame grabber, although more likely a frame grabber connected to a computer. For some systems the FPGA could be partially or fully embedded in the camera(s). The computer system besides performing internal calibration checks, is also programmed to perform image analysis in real-time of the beam as it irradiates the scintillator so as to monitor and analyze in two-dimensions (“2D”) the beam position and beam shape, beam movement, the beam intensity profile including tail, beam fluence and external dosimetry, and beam angular divergence in the case of the beam monitor configuration incorporating two or more scintillators in the beam path and separated by an appropriate distance. In addition, because all of the embodiments incorporate one or more machine vision cameras oriented at an angle to the scintillator plane, all of the camera images will incur perspective/tilt distortion (i.e., keystoning), while the camera lenses, especially due to their close working distance, will exhibit some amount of optical distortion as well as vignetting, and the camera sensors themselves can never be perfectly uniform in terms of each pixel having exactly the same response. All of these system hardware related non-uniformities can be corrected by calibration of the integrated system and frequently checking this calibration by taking repeated images of the system response to the UV-source illuminated scintillator and automatically adjusting the calibration as needed by the computer system.
In order to minimize maintenance and down time, and to further optimize the design, fast scintillator replacement is required in embodiments. This is achieved in all of the embodiments shown in
Embodiments include a number of different light-tight enclosure beam monitors incorporating one or two scintillators and from one (1) to twelve (12) or more cameras, depending upon the desired beam spatial/positional resolution and the required scintillator active area size which for EBRT applications can typically extend up to about 40 cm×40 cm. In general, for a 20 cm×20 cm scintillator, the intrinsic 2D position resolution should be on the order of ˜0.03 to 0.2 mm, depending upon the required UFT beam monitor specifications. However, no matter how many cameras are employed, such as 1, 2, 3, 4, 6, 8, 10, 12 or more (see
Depending upon the application requirements in terms of: image/pixel resolution, low-light sensitivity, pixel bit depth (i.e., gray scale), exposure time (i.e., shutter speed), frame rate, and image processing speed including system latency, camera images can be streamed live, processed and analyzed in real-time at rates potentially as fast as 25-100 μs per image (i.e., 10,000-40,000 fps) depending upon the system hardware, firmware and software, including the choice of camera interface. For example, machine vision cameras operating at over 30,000 fps, corresponding to a timing resolution of ˜33 μs, can still provide sub-mm image resolution for embodiments such as the above multi-camera, 20 cm×20 cm, or even 40 cm×40 cm, scintillator EBRT beam monitors at a cost of about $5K to $8K per camera is single unit quantities. The larger size 40 cm×40 cm scintillator beam monitoring systems in accordance to embodiments employ 4 or more cameras, and are configured if desired with two different types of cameras—for example in a single-scintillator 6-camera configuration there could be four relatively inexpensive high picture resolution, low frame rate (fps) cameras, plus two of the more expensive high fps cameras; other combinations are also possible such as 4 slow and 4 fast cameras, or 4 low sensitivity and 4 high sensitivity cameras in a 8-camera system. In fact, low cost, high spatial resolution, low sensitivity, low fps cameras could even be paired side-by-side with ultra-fast, high sensitivity, ultra-compact PMTs (e.g., Hamamatsu H11934 series with dimensions of 30 mm×30 mm×32 mm) with camera lenses coupled to each PMT thereby viewing the same scintillator area as the camera. The PMTs would provide the low-light sensitivity and dose rate information with ultra-fast ns and sub-ns response capability (e.g., 10 ns is equivalent to 100,000,000 fps). For applications requiring frame rates of 1,000-2,000 fps or slower, smaller size machine vision cameras can be procured for $1K (see below).
In
One embodiment uses Universal Serial Bus (“USB”) as the system interface, hardware and processing software, which is capable of processing and analyzing images at rates up to about 1,000-2,000 fps (i.e., 1.0 ms to 0.5 ms). For higher performance, embodiments use a number of faster camera interfaces for interfacing with high-speed FPGA based frame grabber hardware, firmware and software, to process and analyze the streaming images at much higher speeds, including CoaXPress 2.0 (CPX-12), GigE (10 Gigabit Ethernet), Camera Link HS, etc.
Referring again to
All of the embodiments disclosed herein include at least one UV illumination source, with at least one UV photosensor to monitor the stability of each UV source. The UV source employed in embodiments for the BoPEN scintillator is a UV-LED with peak emission at ˜280 nm, where the BoPEN scintillator film essentially absorbs at least 99% of the source photons at the film surface within a ˜0.1 μm thick layer. The UV photosensor used to monitor the UV-LED in embodiments is a UV-photodiode. If needed, the UV source and/or UV photosensor can be coupled to a suitable UV bandpass or UV shortpass filter. When the rad-damage in any particular area starts to become significant, the scintillator-frame is pushed slightly towards the far side until such time as the frame has been pushed completely to the far side as shown in
If the scintillator 6-way-cross chamber includes both entrance and exit gate valves, then breaking vacuum is limited to the small chamber volume with no impact on the rest of the beamline and so scintillator-frame replacement can be done whenever convenient and should only take about an hour or so including ambient pressurization and re-evacuation. Other features of consequence are the machine vision camera in the top arm, the PMT in the bottom arm, the push-pull linear positioner on the left side, and the reducer nipple on the right side which is connected to a small vacuum pump system (not shown) with a bleed valve for chamber pressurization followed by re-evacuation. Also not shown are the described beam entrance gate valve, although the exit gate valve is easily seen in
To maximize the PMT light collection efficiency a set of highly efficient, high transmission glass (e.g., Schott B270) aspheric condensing lenses are employed with an f/number that can be less than 1.0 (e.g., between f/0.6 to f/0.9). For maximum efficiency, the first condensing lens 1150 is located inside the cross vacuum chamber just below the scintillator/frame, while the second lens 1152 is located just below the glass viewport window 1156 and in front of the PMT at ambient pressure as shown in
The embodiment shown in
As discussed above, for the embodiment shown in
As the integrated exposure of the scintillator to the ionizing beam accumulates over time, so does the radiation dose which would typically be concentrated in or near the beamline cross center 1250 shown in
The embodiment shown in
Depending upon the specific application and beamline monitoring requirements, a number of variations of the 6-way-cross structures described above and in
Not all beamline monitoring systems need to be integrated into a vacuum beam pipe environment, including segments of electron and neutron beam delivery systems. Such systems, however, can still utilize the various multi-arm-cross embodiments disclosed herein. For monitoring the beam in air, the crosses do not have to be evacuated but can simply be made light-tight by adding a thin foil or dark/black polymer film window, or some polymer-foil combination thereof, to the entrance and exit flanges. For enhanced scintillator recovery, the air atmosphere can be replaced by any gaseous atmosphere including oxygen or oxygen enhanced mixtures, or pure nitrogen or argon or any other type of specified atmosphere.
All of the embodiments with cameras include the camera or cameras viewing the scintillator at various angles of incidence or reflection, the latter indirectly via a folded-optics mirror system. Parameter optimization determines the most appropriate camera lens angle of incidence with respect to the normal to the scintillator plane (i.e. surface) or mirror for each application. For most of the embodiments disclosed here, the camera lens viewing angle with respect to the scintillator will typically fall within the range of 25-65°, with an average value of ˜45°. For the camera images captured in
The angular distortion disclosed above caused by the angle of tilt, as shown in
Although the above embodiments have mostly been described and tested in terms of their applicability to proton beams and proton beam therapy, these embodiments are applicable to all types of particle beams including those for particle beam therapy (e.g., protons, helium-ions, carbon-ions, electrons, etc.), as well as neutron particle beams. Fast neutrons can still benefit from the described advantages associated with BoPEN scintillator films, but slow to thermal neutrons require boron or lithium or gadolinium doped scintillators, such as boron doped EJ-254, which is of interest for boron neutron capture therapy (“BNCT”) and gadolinium neutron capture therapy (“GdNCT”). Although most of the disclosed embodiments have referenced the BoPEN scintillator, none of the embodiments are scintillator specific, so any scintillator material can be employed. The described embodiments are also of interest to particle research accelerators. The particle beams used for such research include everything from electron and muon beams, to rare isotope and exotic heavy-ion and radioactive ion beams such as highly charged uranium ions beams (e.g., U-238 with a net charge greater than +60). In addition there are tens of thousands of particle beams used by industry and various versions of these embodiments could find application there.
Embodiments can also be used for external beam radiation therapy (“EBRT”) based on high energy photon beams (e.g., MeV gammas and/or X-rays). Embodiments disclosed herein, such as those in
The highest performance cameras with the largest sensor size, best low-light sensitivity, highest bit depth (i.e., pixel gray scale range), highest frame rates, most sophisticated embedded FPGA circuitry, and thus the highest data transmission output in terms of MB/s, consume the most power. The maximum power consumption for such cameras could be on the order of ˜10 watts per camera, although the standby power when the camera isn't running would likely be much less depending upon the camera. And for smaller cameras, such as those used for the images in
Several solutions exist to the potential problem of heat build-up, including the use of a series of internal baffled air-vents with staggered holes to block light leaks, as for example in
Alternatively the light-tight enclosures can be sealed around the camera lenses, with the camera body protruding out of the light-tight enclosures and thereby venting the camera heat to the external ambient open-air environment. For the 6-way-cross systems, a custom short nipple can be made with a light-tight seal (e.g., double O-ring) to the camera lens, thus leaving the camera body protruding outside and beyond the nipple flange to the external atmosphere. There is also the option of using active cooling of the camera or silicon image sensor, or even cryogenic cooling, as some cameras are sold with thermoelectric cooled sensors. Finally, each camera and/or sensor could be calibrated for their signal response or drift as a function of temperature, and then the temperature of the camera or sensor in its enclosure monitored and its signal response automatically corrected by software.
For the detection of neutrons in EBRT applications, the two most obvious locations for a neutron beam monitoring system might be: (1) immediately after the Li target, but before the moderator, where mostly slow neutrons but perhaps some fast neutrons (e.g. ˜0.8 to 1 MeV) are typically generated by a ˜2.6 MeV proton beam, and (2) at a location after the moderator where the neutron energy is degraded for many boron neutron capture therapy (BNCT) treatment regimens to the epithermal energy range but more broadly across the range from thermal to slow or even fast neutrons. If only one neutron beam monitor is to be employed, the most important location would be right after the moderator and in front of the patient. Recent trials in Finland suggest that 1-30 keV “slow” neutrons constitute a practical energy range for BNCT treatment. Essentially all of the beam monitor embodiments disclosed herein should work well for the detection and monitoring of neutrons created immediately after the Li target in location (1) above, where the neutron intensity of the BNCT machine is estimated to be on the order of ˜1013 n/s, corresponding to about 5×1013 scintillating photons per second from a 0.2 mm thick BoPEN film. Therefore a much thinner scintillator film can to be used to minimize interaction with the beam, and still produce a huge amount of scintillating light. For example, a 12 μm thick BoPEN film scintillator should yield about 3×1012 scintillating photons per second. However, for beam monitoring in location (2), the added moderator plus energy filtering greatly reduces the number of epithermal neutrons by at least several orders-of-magnitude, which are significantly more difficult to detect anyway due to their lower energy than the more energetic “slow” neutrons in location (1). This means that for neutron beam monitoring after the moderator, B10 or another high neutron cross-section isotope (e.g., Li6 or Gd) loaded scintillator is required to increase the deposited energy in the scintillating host. Such scintillators are available in plastic sheets and can be incorporated in the scintillator-frame embodiments disclosed above and shown in
For BNCT head and neck EBRT therapy, the patient's head is typically positioned very close to the neutron beam exit nozzle, and therefore the thinnest profile beam monitors are required corresponding to the largest camera-lens angles with respect to the scintillator normal (e.g., 60°-70°). Modified versions of
For the above disclosed neutron beam monitors, several high neutron cross-section isotope loaded scintillators are available, such as Eljen EJ-254 or Saint-Gobain BC-454 which are both B10 loaded plastic PVT-based scintillators, or cerium activated Li6 doped silicate glass scintillators from Saint-Gobain, although Li6 doped plastics have also been fabricated. For the various neutron capture therapy (“NCT”) applications, including both BNCT and GdNCT (gadolinium-NCT), the neutron beams employed span the energy range from thermal-NCT to fast-NCT (also called FNT), but most NCT programs appear to be based on epithermal-NCT. Unfortunately all of these neutrons are also more damaging to the scintillator material than protons and/or photons, and therefore scintillator replacement would need to occur much more frequently. For this reason the internal calibration scheme employed in the above embodiments is important for the successful implementation of neutron beam monitors, and the fact that scintillator replacement and internal calibration could be accomplished within minutes would be even more beneficial for NCT than for proton or photon EBRT due to more frequent replacement. One method to prolong the useful lifetime of the boron doped scintillator, and therefore not have to replace it as often, is to integrate a motorized X-Y translation stage into the beam monitor enclosure structure and thereby translate the entire system in the X-Y plane in relatively small steps as required, thus moving it around the isocenter and lengthening the period between scintillator replacement—this strategy is conceptually similar to moving the scintillator-frame in small steps in the 6-way-cross via the previously described push-pull linear positioners.
A general complication associated with scintillators for neutron detection is that most neutron sources also generate gammas, and scintillators that detect neutrons will therefore also detect gammas. Most applications, be they medical imaging or homeland security, require neutron detection systems that can effectively discriminate between gammas and neutrons. The disclosed beam monitor embodiments in
In looking into scintillator damage by neutrons, the issue of radiation damage to the beam monitor cameras was also investigated. Experiments indicate that the slow radiation damage over a period of years to the patient viewing cameras in proton therapy treatment rooms is primarily due to neutrons. The main source of these neutrons is not from the proton beam system, although some neutrons are generated in the collimator, but from the patient's interaction and absorption of the proton beam itself—i.e. primarily where the proton beam stops at the tumor site inside the patient. Radiation damage to digital cameras has been studied extensively for the imaging sensors used in space astronomy (mostly CCDs), as well as for other situations in which high neutron fluxes are created and monitored by cameras such as for fusion research. It has been found that although shielding of cameras can be helpful, it is also not so straightforward. One solution is the direct cooling of the camera sensor to about −20° C. or colder, which also eliminates the camera as a heat source and thereby reduces thermal heating causing calibration drift not only of the camera, but also of the UV-LEDs, UV-photodiodes, and possibly even the scintillator response itself.
Camera sensors/electronics are prone to neutron damage because silicon is typically doped with boron to achieve p-type silicon. However, p-type silicon can also be produced by doping with gallium (“Ga”) instead of boron, and in this way fabricate radiation-hardened silicon devices. Both radiation-hardened and radiation-tolerant semiconductors, including CMOS image sensors and cameras are available from several sources, as such sensors and cameras are required for a number of applications including military, aerospace, scientific, and nuclear energy. With conventional boron doped silicon devices, the primary camera visual damage due to neutrons is the creation mostly of “bright” pixels in the silicon image sensor. The “bright” pixels caused by rad-damage are high dark-current pixels or “hot-pixels”. Some embodiments replace the cameras in the beam delivery room every couple of years. The majority of neutrons created are scattered in the proton beam momentum direction, which is towards the opposite side from where the patient is being irradiated and thus towards the back of the room. However the entire room is effected by the scattered neutron field and some neutrons will backscatter towards the cameras located at the beam nozzle exit and in front of the patient. Frequent internal calibration of the beam monitoring system will identify the radiation damaged pixels, and so their contribution to the image analysis can be conveniently eliminated by software. Partial neutron shielding of the cameras can be achieved by several means, including the use of boron doped transparent plastics in front of the camera body and lens, similar to commercially available 5% boron doped PVT plastic scintillators but without the addition of a fluor dopant. Since the cameras themselves are located out of the direct beam path, the entire light-tight camera box enclosure, excluding the entrance and exit window areas, can be fabricated out of a neutron shielding metal sheet such as a boron-aluminum alloy like BorAluminum from Ceradyne (˜4.5% to 8% by weight of B-10 isotope) or AluBor (10% by weight of natural boron) from S-DH, or a boron clad aluminum such as BORAL or BORTEC. Also boron composite plates made with boron fiber can be used. Alternatively, a number of small shielding plates can be strategically placed around each camera body. Another solution for shielding the front of the camera from neutrons is to use a thick, high boron content transparent borosilicate glass (e.g., 3-5% boron) in front of the camera lens, and maybe in front of the entire camera body. There are many borosilicate optical glasses, but Schott N-ZK7 (15% B2O3 by wt.), N-BK10 (13% B2O3 by wt.) and N-BK7 (10% B2O3 by wt., also referenced as Borkron) with 4.7%, 4.0% and 3.1% boron respectively (by weight), or Schott BOROFLOAT-33 with 4.0% boron (i.e., 13% B2O3) are all readily available as is Corning 7740 glass (Pyrex) which is 12.6% B2O3. However BOROFLOAT-33 being much more economical than other borated glasses is sold for neutron shielding in thicknesses up to ˜25 mm. It is noted that extremely high B2O3 and Gd2O3 glasses have been described in the patent literature such as Application PCT/JP2013/069578 which potentially would be more effective. Also a source of heavily doped boron and lithium polyethylene sheets, bricks and rods/cylinders is Shieldwerx (a division of Bladewerx LLC), which sells a 30% natural boron doped polyethylene product called SWX-210 (i.e., contains 1.87×1022 boron atoms per cm3) as well as a 7.5% natural lithium doped polyethylene product SWX-215. The disadvantage of boron doped neutron shielding materials is that each neutron captured by boron generates a 0.42 MeV gamma ray; however, lithium doped shielding materials do not produce any neutron capture gammas. However the lower neutron capture cross-section of Li6 compared to B10, means that a greater thickness of lithium doped material is required than similarly doped borated material.
In terms of neutron damage, at what point the cameras, or possibly just the silicon image sensors, would have to be replaced needs to be experimentally determined, but most likely it will be in years for proton or photon therapy since the internal calibration system can adjust for bad pixels in real-time as they occur. It is also noted that the larger the image sensor pixel size, the less prone it is to radiation damage. For the beamline monitors such as the 6-way-crosses in
Embodiments are directed to external beam radiation therapy (“EBRT”) related applications for both particle and photon radiation. For both types of EBRT, the embodiments are directed towards beam monitoring systems designed for use in either of two locations: (1) internal beam monitors located within the accelerator beam delivery system and therefore prior to the beam exiting the system nozzle or snout or collimator, or (2) external beam monitors located outside the accelerator beam delivery system after exiting the system nozzle or snout or collimator and thus positioned after the delivery system exit and in front of the patient.
Embodiments can further be used for a variety of industrial and scientific beam monitoring applications such as ion implantation accelerators (e.g., depending on ion, typically >0.3 MeV), and nuclear physics particle accelerators. Typically ion beam implantation will have the most stringent detector/monitor design requirements with regard to beam transparency, as the ion particle energies are frequently below 1 MeV and the particles themselves are typically highly ionized, heavy nuclei. Many accelerators used for nuclear physics also operate at relatively low to medium ion energies, so the same beam monitor concept in accordance to embodiments can be used for both applications. Some additional advantages of the described embodiments include the relative low cost of the beam monitor critical hardware, and the low cost lifetime operational/maintenance expense which includes the minimal overhead expense associated with the ultra-fast internal calibration system, as compared with the time consuming calibration cost for conventional systems. This benefit is also important for scientific applications (e.g. nuclear physics) that subject other detectors/monitors to costly maintenance and radiation damage replacement expenses.
The therapeutic benefits of embodiments of UFT beam monitors disclosed herein are particularly useful with “FLASH” irradiation therapy in which short pulses (˜0.5 second) of radiation are delivered at ultrahigh dose rates of ≥10 Gy/s (i.e., FLASH) compared to conventional dose rates of ≤0.03 Gy/s in single doses over a period of ≥60 seconds. FLASH radiotherapy may well result in a paradigm shift in the treatment of cancer as ultrahigh dose rates appear to increase the differential response between normal and tumor tissue, thus increasing the lethality to malignant cells while not significantly increasing damage to healthy cells. In order to monitor the FLASH beam in real-time, the much faster beam profile imaging time and readout capability, greatly improved intrinsic 2D position resolution, and the much higher dose rate capability of the described UFT beam monitors yields order-of-magnitude advantages when compared to conventional ionization chambers, and in this sense appears to be an unexpected enabling technology.
Embodiments include a transmissive ionizing-radiation beam monitoring system comprising an enclosure structure with an ultra-thin, dark colored or black exit window to an incident ionizing-radiation beam; at least one thin scintillator within the enclosure structure that is directly in an incident ionizing-radiation beam path and transmissive to the incident radiation beam; at least one ultraviolet (UV) illumination source within the enclosure structure facing the scintillator for internal system calibration; at least one UV photosensor within the enclosure structure positioned to monitor and calibrate the UV illumination source; and at least one machine vision camera within the enclosure structure located out of an incident ionizing-radiation beam path and comprising a camera body and lens having a projection of its optical axis oriented at an angle of incidence of 50±30 degrees to a surface of the scintillator.
Embodiments further include a computer system comprising a frame grabber to process and analyze image data streaming in real-time from the machine vision camera; a wired cable or wireless data interface connection between the machine vision camera and the computer system; a plurality of machine vision cameras surrounding a scintillator area, each of the plurality of cameras having a corresponding lens focused on and its field of view centered on one particular section of the scintillator area; a UV bandpass filter optically coupled in close proximity to each UV illumination source, the UV bandpass filter having maximum spectral transmission in a spectral region of maximum emission from the UV illumination source; wherein the UV illumination source comprises a UV Light Emitting Diode (LED) comprising an emission peak that corresponds to a strong absorption region of the scintillator with minimal luminous output in a scintillator emission region; wherein the computer system further comprises tracking a beam position and movement, and calculating a beam shape, a beam intensity profile, a beam fluence and external dosimetry in real-time from a streaming digital output of the machine vision camera; wherein the thin scintillator comprises biaxially-oriented polyethylene naphthalate (Bo PEN).
Embodiments include a transmissive ionizing-radiation beam monitoring system comprising a light-tight enclosure comprising an ultra-thin entrance window and an ultra-thin exit window to an incident ionizing-radiation beam, wherein the entrance window and the exit window are highly transmissive to the incident ionizing-radiation beam and comprise one of a dark colored or black polymer film or metal foil, or a composite polymer-foil combination; at least one thin scintillator within the light-tight enclosure that is directly in an incident ionizing-radiation beam path and transmissive to the incident radiation beam; at least one ultraviolet (UV) illumination source within the light-tight enclosure facing the scintillator for internal system calibration; at least one UV photosensor within the light-tight enclosure positioned to monitor and calibrate the UV illumination source; at least one machine vision camera within the light-tight enclosure comprising a camera body and lens system located out of an incident ionizing-radiation beam path; and a mirror in close proximity to each lens and located out of an incident ionizing radiation beam path and obliquely facing both the lens and the scintillator at an angle, wherein the machine vision camera and its associated close proximity mirror comprises a folded optical system configuration with respect to its view of the scintillator surface to reduce a thickness or depth of the light-tight enclosure.
Embodiments further include an ionizing-radiation beam optimized for treating cancer by external beam radiation therapy and comprise one of a particle beam of electrons, protons, ions or neutrons, or a photon beam of X-rays or gamma-rays; wherein the thin scintillator comprises a film or sheet of biaxially-oriented polyethylene naphthalate (BoPEN) falling within a thickness range between 1 μm and 300 μm; the scintillator comprising a roll-to-roll scintillator feed configuration wherein a scintillator film is wrapped around and stored on a small diameter feeder-spool located inside the enclosure and pulled across a beam axis transit window area onto a take-up spool that can be advanced by a stepper-motor rotating a take-up spool spindle to move a new section of scintillator film across the beam window area to replace a previously radiation damaged area; wherein one or both of entrance and exit windows are individually physically coupled by a thin frame to the thin scintillator such that a window/scintillator framed structure comprises a single replaceable module unit that can be accessed from outside the light-tight enclosure; further comprising multiple machine vision cameras surrounding a scintillator area, with each camera having the lens of its folded optical system focused and its field of view centered on one particular section of the scintillator area; wherein a computer system comprising a frame grabber combines data from the multiple cameras to track the beam position and movement across an entire scintillator area and computes the beam shape, a beam intensity profile, a beam fluence and external dosimetry in real-time from a streaming digital output of the machine vision cameras; further comprising multiple machine vision cameras surrounding a scintillator area, with each camera being in close proximity and optically coupled to a small mirror and thereby constituting a multi-camera folded optical system configuration so as to minimize the thickness of the light-tight enclosure; wherein some of the machine vision cameras operate at short exposure times while other machine vision cameras operate at long exposure times; wherein for a dual entrance-exit window/scintillator module system some of the machine vision camera proximity mirror folded optical system units are focused on an entrance scintillator area, with a remainder focused on an exit scintillator area, so that the computer system can calculate a beam angular divergence between the two scintillators while also improving on an accuracy and resolution of the beam position, movement, intensity profile, fluence and external dosimetry.
Embodiments include a transmissive ionizing-radiation beam monitoring system including a vacuum chamber structure with vacuum compatible flanges through which an incident ionizing-radiation beam enters and exits the monitoring system; at least one thin scintillator within the vacuum chamber structure that is transmissive to the incident ionizing-radiation beam and oriented at an angle greater than 10 degrees to a normal of the incident radiation beam; a machine vision camera within an arm or nipple or small enclosure at atmospheric/ambient pressure attached to the vacuum chamber structure by a flange attached to a vacuum-tight viewport window with a camera optical axis oriented at an angle of less than 80 degrees with respect to a normal of the scintillator; at least one UV illumination source facing the scintillator for internal system calibration; and at least one UV photosensor positioned to monitor and calibrate the UV illumination source.
Embodiments further include a multi-arm cross with the camera located within a nipple or small enclosure at ambient pressure that is attached to a flange of a viewport window on one arm of the cross; wherein the thin scintillator is mounted in a frame and attached to a shaft of a push-pull linear positioner that can be pushed or pulled or nudged through a beam area from one side or arm of the cross into an opposite side or arm; wherein the scintillator in its frame is oriented at an angle of 45±25 degrees to the normal of the incident radiation beam and the camera optical axis is oriented at an angle of 45±25 degrees to the normal of the scintillator; wherein the vacuum chamber structure is a 6-way cross with the camera located within a small enclosure attached to the flange of the viewport window on one arm of the cross, and a photomultiplier tube (PMT) or solid state photomultiplier (SSPM) such as a silicon photomultiplier (SiPM) located within a second small enclosure also at atmospheric/ambient pressure and attached to the flange of a second viewport window on the arm opposite the camera; wherein a first condensing lens is located in close proximity to the viewport window in the small enclosure at atmospheric/ambient pressure containing the PMT or SSPM, and a second condensing lens is located on the other side of the same viewport window in the vacuum chamber structure just below the scintillator frame, with the two condensing lenses separated by the viewport window but facing each other belly-to-belly to capture a relatively large solid angle of light from the scintillator and projecting it onto a light sensitive area of the PMT or SSPM; wherein a first scintillator in its frame is located in one arm of the 6-way cross and a second scintillator in its frame is located in the opposite arm of the 6-way cross, with each scintillator attached to its own push-pull linear positioner, and wherein the first and second scintillators do not have to be identical either in composition or in thickness; wherein the scintillator comprises a roll-to-roll scintillator feed configuration wherein a scintillator film is wrapped around and stored on a small diameter feeder-spool located inside the vacuum chamber structure and pulled across a beam axis transit area onto a take-up spool that can be advanced by a stepper-motor rotating the take-up spool spindle to move a new section of scintillator film across the beam axis transit area to replace a previously radiation damaged area.
Embodiments include a method of monitoring a beam of ionizing-radiation, including tracking of beam position, movement, intensity profile, beam fluence and external dosimetry, with a rapid internal calibration system, the method comprising: receiving the ionizing-radiation beam in a transmissive thin scintillator enclosed in a light-tight structure with entrance and exit highly transmissive to the incident radiation beam, a folded optical system comprising at least one mirror and one machine vision camera, at least one UV illumination source facing the thin scintillator and at least one UV photosensor positioned to monitor the UV source, a computer system comprising a frame grabber and a wired cable or wireless data interface between each machine vision camera and the computer system; creating a multitude of emitting photons some of which are captured by the machine vision camera folded optical system in real-time; causing a series of streaming images from each machine vision camera to the computer system; wherein the computer system processes and analyzes in real-time the image data streaming from the machine vision cameras to track the beam position, movement, intensity profile, beam fluence and external dosimetry; wherein the rapid internal calibration system periodically activates the UV-source to illuminate the thin scintillator over its entire active area while the UV-photosensor monitors the UV-source to correct for any UV-source signal drift or instability over time, while the machine vision camera folded optical system streams images of the scintillator photon emission over its active area; wherein the computer system compares the machine vision camera digital image output to previously stored digital image output taken of the thin scintillator under the same conditions and in this manner monitors the system stability over time and internally calibrates the system for small changes in performance, and signals when a change in the scintillator component is required according to pre-programmed guidelines, or flag if any other hardware or software problems are detected.
Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the disclosed embodiments are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.
Claims
1. A transmissive ionizing-radiation beam monitoring system comprising:
- an enclosure structure with an ultra-thin window to an incident ionizing-radiation beam;
- at least one thin scintillator within the enclosure structure that is substantially directly in an incident ionizing-radiation beam path;
- at least one ultraviolet (UV) illumination source within the enclosure structure;
- at least one UV photosensor within the enclosure structure; and
- at least one machine vision camera within the enclosure structure.
2. The transmissive ionizing-radiation beam monitoring system of claim 1, further comprising:
- a computer system that processes and analyzes image data streaming in real-time from the machine vision camera.
3. The transmissive ionizing-radiation beam monitoring system of claim 1, further comprising:
- a UV bandpass filter optically coupled in close proximity to each UV illumination source, the UV bandpass filter having maximum spectral transmission in a spectral region of maximum emission from the UV illumination source.
Type: Application
Filed: Nov 27, 2019
Publication Date: Apr 9, 2020
Applicant: Integrated Sensors, LLC (Ottawa Hills, OH)
Inventor: Peter S. FRIEDMAN (Ottawa Hills, OH)
Application Number: 16/697,439
