Patent Grant
7706506
In transfusion and transplant medicine, the transfusion of blood or blood components sometimes results in TA-GVHD (Transfusion Associated-Graft-Versus-Host Disease). Although rare, TA-GVHD results in a mortality rate of greater than 90% of cases, when this complication occurs. At this time there is no known, effective treatment for TA-GVHD. Without available treatment, the only method of dealing with TA-GVHD is prevention. Today, the only accepted method of prevention for TA-GVHD is in the FDA prescribed dose of ionizing radiation, provided by either gamma emitting radioactive sources or by X-ray sources, applied to pre-transfused, blood and blood components in transfusion medicine. However, cost and size of commercially available X-ray source irradiation equipment prevents deployment at all transfusion facilities and other locations where blood transfusions occur.
A primary object of the subject X-ray irradiation system described herein is for the irradiation of pre-transfused blood, blood components and marrow transplants in transfusion medicine.
Another key object of the invention is to provide a system with a greater uniformity of both the X-ray energy and it's intensity across the field of radiation and to reduce the necessity for large distances between the X-ray source and the material being irradiated. By reducing this distance, less shielding is required as the object/material being irradiated may be positioned close to the X-ray source, thereby reducing the volume that requires radiation shielding. Through “transmission geometry,” greater efficiency (nearly twice that obtained in “reflection geometry”) is achieved in converting electron beam energy into X-ray radiation.
Still another object of the X-ray irradiation system can be used in irradiation applications in life science research. Also, the X-ray source radiation technology may be used in other irradiation applications.
These and other objects of the present invention will become apparent to those familiar with X-ray blood irradiation systems and equipment when reviewing the following detailed description, showing novel construction, combination, and elements as herein described, and more particularly defined by the claims, it being understood that changes in the embodiments to the herein disclosed invention are meant to be included as coming within the scope of the claims, except insofar as they may be precluded by the prior art.
The accompanying drawings illustrate complete preferred embodiments in the present invention according to the best modes presently devised for the practical application of the principles thereof, and in which:
For the blood transfusion market, commercially available X-ray source blood irradiation equipment is based upon technology such as prior-art industrial, “reflective geometry” continuous emission X-ray source 100, shown in
Low voltage power is supplied to thermionic electron emission cathode filament 108 via electrodes 107. Current flowing through cathode filament 108, heats cathode filament 108, resulting in thermionic emission of electrons. High voltage applied between cathode filament 108 and reflective anode target 110 creates a high magnitude electric field between these two components of X-ray source 100. Thermally emitted electrons from cathode filament 108 are accelerated by the high magnitude electric field toward reflective anode 110. These electrons are focused on a small target area of anode 110 and impact anode 110, resulting in X-ray production. A small originating point source, conical shaped X-ray beam 114 is emitted from anode 110, and exits evacuated enclosure 102 through X-ray window 112. The electrons impacting the small target area of anode 110 generate heat and require that a coolant 106 be passed through cooling chamber 104 in order to cool X-ray source 100.
The required constant potential high voltage power supply is complex in design, large in size (since it typically uses large, heavy transformers) and is expensive to produce.
Disadvantages of X-ray source 100 include: a) low efficiency in converting electron energy to X-ray energy in the target of anode 110; and b) the conical shaped X-ray beam 114 emanating from anode 110. A cross-section of X-ray beam 114 approximates a circle, the diameter of which is dependent upon a distance 118 from X-ray source 100. For example, in one commercially available blood irradiation system, the distance 118 from X-ray source 100 to a material/object 116 for irradiation (e.g., a blood container) is approximately 23 cm (9 inches). This distance 118 is required in order to provide an irradiation field large enough to cover the dimensions of a typical blood container (e.g., a blood bag). In this example prior art system, X-ray beam 114 at a distance of 23 cm from X-ray source 100 is approximately 15.5 cm (6 inches) in diameter. This example irradiation system uses two opposing X-ray sources 100 with a distance of approximately 50 cm (20 inches) between the two sources, resulting in the need to shield a large volume that includes two X-ray sources 100, the space between the sources and the sample container, with lead shielding to prevent X-ray radiation external to this volume. The inverse square law dependence of irradiation intensity with the distance of the material being irradiated from X-ray source 100 results in greater non-uniformity in the radiation received by the material/object 116 being irradiated, and a longer time period is required to reach a required total absorbed irradiation dosage.
The point sources of the anodes in the prior art examples of
Most of the disadvantages of small originating spot, “reflective geometry” X-ray production, as shown in
While the target foil 316 and filter plate 318 are shown outside the vacuum chamber in
In the example of
A controller 302 receives feedback from a solid-state X-ray radiation sensor 326 that measures the total, absorbed radiation density received by material 322 and controls operation of power supply 304 to generate X-ray beam 320 such that the required dose of X-rays is received by material 322. Controller 302 may receive input from other sensors and input from one or more users without departing from the scope hereof.
The shape and size of the cross-sectional area of field electron emissive surface 310 may be selected to form a desired shape and size of the cross-sectional area of X-ray beam 320. For example, a rectangular field electron emissive surface 310 is used to generate a rectangular cross-sectional shaped X-ray beam 320, a circular field electron emissive surface 310 is used to generate a circular cross-sectional shaped X-ray beam 320, a square field electron emissive surface 310 is used to generate a square cross-sectional shaped X-ray beam 320, an oval field electron emissive surface 310 is used to generate an oval cross-sectional shaped X-ray beam 320, and so on.
Power supply 304 includes a DC supply 303 for charging Marx generator 305. Marx generator circuits (e.g., Marx generator 305) are well known in the power supply art, and will therefore not be described in detail herein. In summary, Marx generator 305 multiplies an input DC voltage (e.g., supplied by DC supply 303) to generate a negative high voltage output pulse under control of controller 302; controller 302 may control one or both of DC supply 303 and Marx generator 305. For certain applications of system 300, pulse width, pulse frequency and magnitude of the negative, pulsed, high voltage applied to cathode 308 (and thus electron emitter surface 310) may be pre-set and fixed thereby requiring no interaction by an operator. For example, FDA requirements specify an absorbed radiation dose for each bag of blood. This dose is a fixed quantity and power supply 304 may be pre-configured to deliver the required dose.
Electron emitting surface 310 is positioned a short distance (e.g., between 0.5 cm to 3 cm) from light metal foil 314 of vacuum chamber 306. A negative output of high-voltage pulsed power supply 304, shown within a chamber 407 near vacuum chamber 306, connects to cathode 308 via high voltage connector 406. Power supply 304 is preferably located within chamber 407 but may be located elsewhere, such as external to chamber 407, without departing from the scope hereof High voltage power supply 304 generates negative high-voltage pulses with pulse widths between 50 nanoseconds and 1 millisecond, and preferably between 100-500 nanoseconds, at a frequency between 0.1 Hz and 400 Hz, and preferably at a frequency between 5 and 10 Hz.
Foil 314, forming electron window 315, is supported by equally spaced ribs 409. Rib spacing is based upon both thickness of foil 314 and cross section of ribs 409. In a preferred embodiment, ribs 409 are stainless steel with a cross section of 2×5 mm and a spacing of 2 cm, and foil 314 is titanium with a thickness of 2 mils (50 μm). Foil 314 is sealed with respect to chamber walls 451 thereby preserving the vacuum within chamber 306. Foil 314 is for example a thin light metal (i.e., having a low atomic number) such as titanium, titanium alloys, vanadium, chromium, cobalt, stainless steel and nickel with a thickness of 2 mils (50 μm).
Foil 314 and supporting ribs 409 operate as an anode 457 for cathode 308 and form a transmission window for electrons emitted by field electron emitting surface 310. In one example, vacuum chamber 306 is grounded, thereby maintaining anode 457 at ground potential.
X-ray emitter target foil 316 is positioned external to, at a short distance (e.g., between 5 mm and 30 mm) from, and parallel with, foil 314 of chamber 306. As high velocity electrons strike target foil 316, X-ray radiation is generated. Target foil 316 is attached (e.g., bonded for good thermal contact) to a thin (e.g., between 0.2 mm and 4 mm) aluminum (or copper) plate 318. Aluminum plate 318 is attached to the side of target foil 316 from which X-ray radiation emanates and removes (i.e., filters) the non-useful, low energy part of the X-ray spectrum emitted from target foil 316. Thus, only the desired X-ray spectrum passes through an opening 458 beneath target foil 316 and aluminum plate 318 to reach material 456.
A fan 412 is located in an air inflow channel 413 and operates to force air through a passageway 414, between foil 314 and target foil 316, and then out of an air outflow channel 415. Fan 412 thereby provides cooling to target foil 316. Aluminum (or copper) plate 318 also dissipates heat generated in target foil 316.
Appropriate thickness of shielding 416 and the shapes of chamber 306, inflow channel 413, outflow channel 415, and irradiation chamber 460 ensure safe operation of system 400. Shielding 416 is for example lead, although other radiation blocking material may be used without departing from the scope hereof.
In the example of
In one example of operation, a negative high voltage pulse, with respect to ground potential of anode 457, is generated by power supply 304 and applied to cathode 308. This high voltage pulse generates an electric field between electron emitting surface 310 and foil 314 resulting in the emission of electrons 312 (see
Each high voltage pulse produces a certain amount of X-ray radiation to provide a required, total absorbed dose of X-ray radiation to irradiate the contents of transport vehicle 417. More than one pulse of X-ray radiation may be required to achieve the desired total absorbed dose. The frequency and duration of these high voltages pulses applied to cathode 308 determines the amount of X-ray radiation generated to achieve a total absorbed radiation dose by the contents of transport vehicle 417.
Alternative methods for positioning material to be irradiated within irradiation chamber 460 may be used without departing from the scope hereof. For example, as shown in
Where the material being irradiated is contained within a bag, such as a blood bag, material container 572 preferably includes a lid 573 that is transparent to X-ray radiation and functions to compress the blood bag to have a uniform depth for irradiation.
In an alternate embodiment, shown in
In yet another embodiment, shown in
The size of field electron emitting surface 310, and associated size of foil target 316, is selected to provide X-ray beam 320 with a cross-sectional area that is sufficient to cover the material to be irradiated (e.g., a blood bag). Thus, the material receiving the irradiation may remain stationery within irradiation chamber 460 while being irradiated.
By combining a cathode with a large field electron emitting surface and a correspondingly large area target foil, a substantially parallel X-ray beam with a large cross-sectional area is generated. Cathode 308, with large field electron emitting surface 310, emits a large electron beam 312 towards target foil 316 which in turn emits a correspondingly sized, forward directed, X-ray beam 320 that is uniform in both energy and intensity, and has a spatial distribution of beam intensity and intensity-energy that is much more homogeneous than from prior-art X-ray sources.
The use of a pulsed, high voltage power supply 304 (e.g., including a Marx Generator) eliminates the disadvantages of the constant potential, high voltage power supply typically used with prior-art X-ray generation. Pulsed high voltage power supply 304 (a) may be operated at higher voltage (e.g., −200 kV to −1000 kV) as compared to 80 kV-200 kV for a prior art X-ray source; (b) may require significantly less power (e.g., 0.5 kW-3.0 kW) as compared to 5.0-10 kW for the prior-art X-ray source; (c) does not require initial warm-up (i.e., a time period during which voltage and current are gradually increased to operating levels for the prior-art X-ray source); (d) does not produce unaccounted for radiation resulting from an interruption of input power during warm-up of a constant potential high voltage power supply; (e) has fewer challenges with high voltage isolation; and (f) is less complex in design and construction than a conventional power supply for a prior-art X-ray source and therefore costs less.
Further, the distance between the X-ray source and the material 322 to be irradiated is not dependent upon X-ray beam divergence, since X-ray beam 320 is composed of substantially parallel lines of X-ray energy with a cross sectional area approximately equal to the area of field electron emitting surface 310. Thus, material 322 may be located a short distance from opening 458 of irradiation chamber 460 and still receive uniform irradiation.
In one example of operation, a high-voltage pulse, having a negative polarity with respect to thin foil 906, is generated by a power supply 918 and applied to cathode 902 such that emissive surface 904 emits electrons. These electrons are accelerated towards, and through, thin metal foil 906 to impact upon coating 912 and generate X-ray radiation. Cylinder 914 filters weaker X-ray energy, and radial X-ray energy 916 is emitted from X-ray radiation source 900. Power supply 918 may be similar to power supply 304 and include a Marx generator, for example. Thus, operation of X-ray source 900 is substantially similar to operation of X-ray system 300.
X-ray radiation source 900 may be formed as other shapes to generate alternative X-ray radiation patterns without departing from the scope hereof. For example, X-ray radiation source 900 may be shaped as one or more of a cube, a sphere, a cone, a prism, a polyhedron, and a pyramid.
While the invention has been particularly shown, described and illustrated in detail with reference to the preferred embodiments and modifications thereof, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention as claimed except as precluded by the prior art.
This non-provisional patent application claims the benefit of an earlier filed provisional patent application Ser. No. 61/013,939, by the subject inventors, and filed on Dec. 14, 2007.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4887604 | Shefer et al. | Dec 1989 | A |
| 6212255 | Kirk | Apr 2001 | B1 |
| 6614876 | Kirk | Sep 2003 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 61013939 | Dec 2007 | US |
