Patent Publication Number: US-6212255-B1

Title: System for X-ray irradiation of blood

Description:
The present application claims the priority date of U.S. Provisional Patent Application Ser. No. 60/098,884 filed on Sep. 2, 1998 in the name of Randol E. Kirk, the inventor herein. 
    
    
     BACKGROUND OF THE INVENTION 
     X-Ray irradiation of blood plasma is one of the methods sanctioned by the U.S. Food and Drug Administration for providing a product which diminishes the chance of transfusion-induced diseases. For this purpose, the radiation dose and dose distributions that may occur from X-ray sources must be controlled accurately for meeting regulatory requirements. X-ray irradiation for sterilization has several advantages over gamma ray irradiation, electron beam application and other types of blood purification. First, X-rays can be accurately controlled in application and secondly, equipment for providing the X-rays is relatively safe, and also, the equipment for providing the X-rays is comparatively inexpensive as compared to the other types of blood purification. 
     SUMMARY OF INVENTION 
     The inventive blood irradiator provides a uniform dose of X-ray beam irradiation for a blood plasma contained in a blood transfusion bag. In one embodiment, the bag is placed in a selected cannister for receiving the X-ray beam, and the system includes two X-ray tubes positioned to irradiate the bag from opposite sides to provide a uniform radiation to the blood in the bag. 
     The foregoing features and advantages of the present invention will be apparent from the following more particular description of the invention. The accompanying drawings, listed herein below, are useful in explaining the invention. 
    
    
     FIG. 1 is a view showing a schematic of a basic structure of the inventive system; 
     FIG. 2 is a view showing a blood transfusion bag and the cannister for receiving the bag; 
     FIG. 3 is a sketch showing the positioning of the X-ray tubes relative to the cannister of one embodiment of the invention and is useful in explaining the apparatus for irradiating the bags; 
     FIG. 4 is a sketch of an embodiment of the invention using a single source of irradiation; 
     FIG. 5 is an embodiment of the invention wherein the machine  12  includes a sliding door for closing the irradiation chamber; and 
     FIG. 6 shows an embodiment of the invention having hinged door for closing the irradiation chamber. 
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention provides an apparatus for insuring dose uniformity for a blood contained in a transfusion bag that receives X-ray beam radiation from X-ray tubes. 
     Referring to FIGS. 1-3, the inventive X-ray system  11  comprises a suitably shielded apparatus or machine  12 , which may be portable. The machine  12  includes a first X-ray tube or source  15  which is oriented to provide a beam of X-rays downwardly, indicated by the dotted lines  16 , to a chamber  19  which is adapted to receive a cannister or container  18  for the blood plasma bag. 
     The cannister  18  has an oval shaped interior for receiving the transfusion bag  20 , and includes a cover or top  21 , see FIG.  2 . The cannister  18  is dimensioned and positioned to maintain the blood plasma transfusion bag  20  at a precise distance and position relative to the X-ray tube  15 , see FIG.  3 . Cover  21  controls the depth or thickness of the blood bag  20  within cannister 18 . Importantly, the cannister  18  is dimensioned to receive the cover  21  to maintain the thickness of 4 cm throughout the bag. The system includes suitable radiation security switches so that X-ray exposures can be initiated only when all the radiation doors have been closed, as is known. 
     In the embodiment shown, X-ray tube  15  has an output of 160 kV and the X-ray beam output port of tube  15  is designed to provide a relatively wide X-ray beam of 40-50 degrees in order to provide a beam with a sufficiently large diameter to fully cover the cannister  18  and the included bag  20 , as will be discussed. The X-ray tube is positioned relatively close, that is 23 cm, from the upper surface of cannister  18  to assure that maximum energy is delivered to the bag  20 . As is known, the closer an X-ray source is to object to be irradiated, the higher the energy delivered to the object; that is, the level of the energy delivered to the object is dependent on the distance between the two components. As is also known, the object can be irradiated faster when more energy is delivered to the object. 
     It is of particular importance that the irradiation received by the blood plasma in bag  20  be uniform. That is, the blood in the bag must be uniformly irradiated; that is, irradiation energy within a specified range must be provided to the blood for the same period of time to meet Federal regulations. For this purpose of providing an efficient uniform irradiation of the blood plasma bag, in the embodiment of FIGS. 1-3, a second X-ray tube  17  is provided on the opposite side of the cannister  18 . The X-ray tube  17  is essentially identical to X-ray tube  15  and provides energy to the opposite surface or side of the bag  20 . Tube  17  is positioned the same distance from the cannister as is tube  15 , that is at 23 cm from the lower surface of cannister  18 . Hence, the transfusion bag  20  is concurrently irradiated from two separate X-ray sources for a precise time. 
     In the embodiment of FIG. 1, the two X-ray tubes  15  and  17  are powered by the same power supply from an AC source connected through adapter  29 . Two separate power sources may be provided. 
     It is clear from FIG. 2, that the irradiation energy from X-ray tube  17  complements the irradiation energy from X-ray tube  15 . Since the energy level varies as the beam penetrates the 4 cm thick bag of blood; the energy provided changes with the depth or thickness of the blood in bag  20 . (As stated above, the thickness of the bags is a maintained at 4 cm by the cannister.) The energy from tube  15  is maximum at the top surface of blood bag  20  and decreases as it penetrates the bag  20 , and is effectively at a minimum level at the lower surface of bag  20 . Conversely, the radiation energy from X-ray tube  17  is maximum at the lower surface of bag  20  and decreases to a minimum at the top surface of bag  20 . The relation of the irradiation energy at any level or depth of bag  20  is a sum of the energy developed by the two tubes. In practice it has been found that irradiation of a blood plasma bag for about six minutes with the apparatus disclosed complies with Federal regulations. 
     The blood in bag  20  becomes a factor in controlling the dose distribution for the irradiation. The kV, mA, time and filtration of the beam are carefully controlled to assure that the applicable dose delivered to all parts of the bag is similar. Transfusion bags vary in both size and configuration and the cannister  20  accommodates the different varieties while maintaining a maximum thickness of 4 cm or less. As is known, X-ray energy is absorbed in a particular item as a function of density of the material and depth to be penetrated. 
     In the particular embodiment of FIG. 1, the energy level of the X-ray tubes is 160 kV. It has been found that to maintain uniformity of radiation to all parts of the bag, the tubes must provide each at least 150 kV output to comply with the FDA specifications that the irradiation be within a range of 1500-2500 rads. The X-ray tubes  15  each irradiate the bag  20  with a surface dose of 2500 rads and an exit dose of 1500 rads. Present requirements are that the bag be irradiated for a six minutes. Ideally, the irradiation dose effective at the center of the blood plasma in bag  20  is the same as the dose at the blood plasma adjacent the opposite (upper and lower) surfaces of the bag. 
     Further, it has been found that the output port of each of the X-ray tubes  15  and  17  should preferably have a diameter to provide a 45 degree beam such that the beam has at least a diameter of 15.5 cm at 23 cm distant from the tube. This permits the tubes to be placed closer to the bag, since as is known, the effective radiation is dependent on the distance of the object from the source. 
     It has also been found important to provide an efficient ion pump to maintain a good vacuum in the X-ray tube. An ion pump is preferred since the tube is used frequently for short periods, and hence any impurities in the vacuum can not be purged merely by usage and heating of the tube. Thus an efficient ion pump is used. In the embodiment shown the tubes both have a rating of 160 kV; however, theoretically the tubes could have different outputs rating. The 160 kV tubes are commercially available tubes with known characteristics and are manufactured by various reliable sources. 
     The bags  20  used in blood transfusion bags vary in both size and configuration. The cannister  18  accommodates the different varieties of bags while maintaining the bag at a maximum thickness of 4 cm or less. This insures the dose delivered to any part of the blood will be no more than 2500 rads and no less than 1500 rads, all per FDA specifications. The size of the chamber is related to the minimum width of the variety of blood bags to be accommodated. As depicted in FIG. 2, in one embodiment the dimensions of cannister are 15.5 cm×12 cm×4 cm, and cannister contains the bag  20  in a snug tight position. An important concept in this application is that the transfusion bag  20  is held at a maximum thickness of 4 cm throughout. 
     As mentioned above, X-ray energy is absorbed in a particular material as a function of density and depth to be penetrated. As alluded to above it is important in system  11  that the distance from the X-ray source  15  to the upper surface of bag  20  is 23 cm, and the distance to the lower surface of the bag  20  is 27 cm. The configuration is symmetrical; that is, the distance from the X-ray source  17  to the lower surface of the bag  20  is 23 cm, and the distance to the upper surface of the bag  20  is 27 cm. 
     FIG. 5 shows an embodiment of the inventive system  11  wherein the machine  12 A includes a door  29  mounted on a pivot to slidably close the irradiation chamber  19 . FIG. 6 shows an embodiment of the invention wherein the machine  12  includes a hinged door  31  with a plug  32  for closing the irradiation chamber  19 . 
     FIG. 4 depicts a second embodiment of the invention wherein a blood plasma bag  20  is positioned to be irradiated by a single X-ray tube  15 A. In this embodiment, the plasma bag  20  is mounted in a vertical orientation, that is its longest length is vertical and its 4 cm thickness is positioned vertically as contrasted to the horizontal orientation of the bag  20  shown in FIGS. 1-3. A first surface or side of the plasma bag  20  is irradiated for a preselected time period. Next, rotatable support  28  rotates the bag about its vertical axis, and the opposite surface of the bag  20  irradiated for an equal period of time. The cumulative irradiation provided to the opposite surfaces or sides is thus effective to provide a uniform irradiation to the blood contained in the bag. 
     While the invention has been particularly shown and described with reference to a particular embodiment thereof it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.