Radiant energy – With charged particle beam deflection or focussing – With detector
Reexamination Certificate
2000-01-03
2001-08-28
Anderson, Bruce C. (Department: 2881)
Radiant energy
With charged particle beam deflection or focussing
With detector
C250S367000
Reexamination Certificate
active
06281509
ABSTRACT:
BACKGROUND OF THE INVENTION
High energy proton irradiation is a recent development in the treatment of cancer and other diseases. A high-energy proton beam is used to deliver radiation as precisely as possible to a tumor volume, minimizing radiation delivery to healthy tissue.
One of the challenges in so using a proton beam is the precise positioning of the patient (and tumor). It has been suggested that the proton beam itself can be used to position the tumor, both before and during treatment. Romero, J. L., et al., 1995 Nucl. Instr. Meth., A 356, 558. If a high energy proton beam is used, such that the protons are not stopped inside the patient, the protons can be used to generate a density image of the patient. Romero, et al., suggested generating such an image through the use of wire chambers to determine proton location and layers of plastic scintillators monitored by photomultiplier tubes to determine proton energy. This method assumes, however, that a proton's energy is absorbed in part in the patient but that its direction remains unchanged. In fact, protons are scattered and often exit the patient in a direction different from the incident direction, thereby degrading the image quality. If it is possible to determine a proton's direction after exiting the patient, scattered protons can be identified and discarded. Other protons that are also included in radiation “background” can also be identified and discarded. The present invention allows the precise tracking, i.e. the determination of the location, energy and direction, of a proton.
The present invention is a method and apparatus for imaging objects. It does so by the 3-dimensional tracking of protons that have passed through the object to be imaged. The tracking is accomplished by gathering and analyzing images of the ionization tracks of the protons in a closely packed stack of scintillating fibers. The fibers are arranged in stacked layers with the fibers in a given layer orthogonal to those in the layers immediately adjacent.
A similar arrangement of scintillating fibers has been used to determine the location of the incidence of ionizing radiation. No suggestion was made, however, for its use in determining the direction or energy of the ionizing radiation. Fenyves U.S. Pat. No. 5,103,098.
A similar arrangement of scintillating fibers has also been proposed for measuring solar neutrons in the 20-200 MeV range. Measurements of the solar neutrons are proposed by imaging the ionization tracks of protons produced as a result of the elastic scattering of the solar neutrons off hydrogen within the scintillating fibers. Ryan, et al., 1997 SPIE, Vol. 3114, 514. No suggestion was made, however, for its use in any type of imaging of objects through which protons have passed, the protons being tracked having been produced within the scintillating fibers of the detector.
The present invention can be used to generate density images of patients for diagnosis and treatment. It can also be used to generate density images of other objects. It can also be used, for example, to measure the thickness at various points of objects of uniform composition.
The present invention has significant advantages as opposed to existing systems of imaging using protons. As noted above, it precisely tracks the protons, determining the direction, as well as the location and energy, of each proton that has passed through the object to be imaged. This capability allows the effective identification and substraction of radiation background, permitting a higher signal to noise ratio and higher contrast images. The present invention also permits real-time imaging.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a new method and apparatus for imaging an object through the 3-dimensional tracking of protons that have passed through the object. A further object of the present invention is to accomplish the 3-dimensional tracking of the protons by gathering and analyzing images of the ionization tracks of the protons in a closely packed stack of scintillating-fibers.
The present invention comprises a plurality of scintillating fibers arranged in a stack; a system for gathering the images of proton ionization tracks in the scintillating fibers; and a system for analyzing the images of the proton ionization tracks to create an image of the object.
The scintillating fibers in a preferred embodiment are arranged in a stack comprising a plurality of stacked layers with the fibers in a given layer positioned lengthwise and substantially parallel to each other. Each layer is one fiber diameter in depth and substantially parallel to each adjacent layer. The fibers in a given layer are positioned orthogonally to those in immediately adjacent layers.
The system for gathering the images of proton ionization tracks in the scintillating fiber stack comprises an energy measuring system, a recording system, and a processing system. One end of each fiber in the stack is coupled to the energy measuring system, and the other end of each fiber is coupled to the recording system. In a preferred embodiment, the energy measuring system comprises one or more photomultiplier tubes, and the recording system comprises one or more chains of fiber-optic tapers, first and second image intensifiers, and charge-coupled device (“CCD”) cameras.
When one of the protons strikes a scintillating fiber, it produces photons within the fiber by the scintillation process. Photons are collected and processed at both ends of the fiber. The energy measuring system collects photons from one end of each of the fibers that has been struck. When the aggregate photons so collected indicate an energy deposited in the fiber stack within an established energy deposit window, the energy measuring system provides a signal to a trigger logic circuit. At the other end of each of the fibers that has been stuck, the recording system captures and holds photon images when the trigger logic circuit registers the proper coincidence.
The photon images are then fed into the processing system, which in a preferred embodiment comprises at least one digital processor and software, enabling storage and display of a form of the photon images. The form of the photon images may be either raw data or processed data. The processed data enables the analysis and display of an image of the ionization track, i.e. the location, energy and direction, of each incident proton that has passed through an object to be imaged.
The processed data is, in turn, fed into a system for analyzing the images of the proton ionization tracks. In a preferred embodiment, this system comprises at least one digital processor and software. This system analyzes the images of proton ionization tracks to create an image of the object.
REFERENCES:
patent: 5103098 (1992-04-01), Fenyves
patent: 5374824 (1994-12-01), Chaney et al.
patent: 5714761 (1998-02-01), Fay
patent: 5905263 (1999-05-01), Nishizawa et al.
patent: 6008496 (1999-12-01), Winefordner et al.
Macri John R.
McConnell Mark L.
Ryan James M.
Anderson Bruce C.
Devine, Millimet & Branch P.A.
Remus Paul C.
Sullivan Todd A.
University of New Hampshire
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