Patent Application
20110009686
1. Field
The present application relates to methods for the production of brachytherapy and radiography targets.
2. Description of Related Art
Conventional methods for producing brachytherapy seeds involve non-irradiated wires (e.g., non-irradiated iridium wires) that are subsequently provided with the desired activity. The desired activity may be provided thereto through neutron absorption in a nuclear reactor.
Brachytherapy seeds have also been produced from irradiated wires. With regard to the production of the seeds, the irradiation of long wires has been suggested, wherein the irradiated wires are subsequently cut into individual seeds. However, because of flux variations in a reactor, the attainment of seeds with uniform activity is difficult.
A method for producing uniform activity targets according to an embodiment of the invention may include arranging a plurality of targets in a holding device having an array of compartments. Each target is assigned to a compartment based on a known flux of a reactor core so as to facilitate an appropriate exposure of the targets to the flux based on target placement within the array of compartments. The holding device is positioned within the reactor core to irradiate the targets. The targets may be formed of the same or different materials and may be placed individually or in groups in the compartments.
The targets may be radially arranged such that more targets are grouped together in compartments that are at a greater radial distance from a center of the holding device. The targets may also be axially arranged such that more targets are grouped together in compartments in axial portions of the holding device that are subjected to higher flux during irradiation. Furthermore, more targets may be grouped together in compartments that are in closer proximity to the flux during irradiation.
The targets may also be arranged based on their self-shielding properties. For instance, targets with lower self-shielding properties may be grouped together in one or more compartments, while targets with higher self-shielding properties may be separated from each other so as to be grouped in different compartments.
The targets may also be arranged based on their different cross sections. For instance, targets having lower cross sections may be arranged in one or more compartments that are in closer proximity to the flux during irradiation. The number of targets in a compartment may be increased so as to decrease a resulting activity of each target in the compartment after irradiation. The method for producing uniform activity targets may further include waiting a predetermined period of time for impurities to decay after irradiation prior to collecting the irradiated targets.
A method for producing uniform activity targets according to another embodiment of the invention may include positioning targets within a holding device according to a predetermined or subsequently determined target loading configuration. The determined target loading configuration is based on a required flux for each target in conjunction with a known environment of a reactor core that is used to irradiate the targets. The determined target loading configuration may be in a form of a ring pattern and/or correspond to a shape of a target plate of the holding device. As a result of the determined target loading configuration, a target may be subjected to uniform or non-uniform flux.
A method for producing uniform activity targets according to another embodiment of the invention may include arranging a plurality of targets in a holding device having an array of compartments, each target being assigned to a compartment based on a known flux of a reactor core so as to facilitate an appropriate exposure of the targets to the flux based on target placement within the array of compartments. The holding device is positioned within the reactor core to irradiate the targets. The targets may be formed of different natural or enriched neutron-absorption isotopes and may be arranged by isotope type, cross section, and self-shielding properties.
The various features and advantages of the non-limiting embodiments herein may become more apparent upon review of the detailed description in conjunction with the accompanying drawings. The accompanying drawings are merely provided for illustrative purposes and should not be interpreted to limit the scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. For purposes of clarity, various dimensions of the drawings may have been exaggerated.
It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It should be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments.
Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
A method according to the present invention enables the production of brachytherapy and/or radiography targets (e.g., seeds, wafers) in a reactor core such that the targets have relatively uniform activity. The targets may be used in the treatment of cancer (e.g., breast cancer, prostate cancer). For example, during cancer treatment, multiple targets (e.g., seeds) may be placed in a tumor. As a result, targets having relatively uniform activity will provide the intended amount of radiation so as to destroy the tumor without damaging surrounding tissues. The device of producing such targets is described in further detail in “BRACHYTHERAPY AND RADIOGRAPHY TARGET HOLDING DEVICE” (HDP Ref.: 8564-000184/US; GE Ref.: 24IG237430), filed concurrently herewith, the entire contents of which are incorporated herein by reference.
The alternately arranged target plates 102 and separator plates 104 are sandwiched between a pair of end plates 106. A shaft 108 passes through the end plates 106 and the alternately arranged target plates 102 and separator plates 104 to facilitate the alignment and joinder of the plates. The joinder of the end plates 106 and the alternately arranged target plates 102 and separator plates 104 may be secured with a nut and washer arrangement although other suitable fastening mechanisms may be used. Furthermore, although the target holding device 100 is shown as having a single shaft 108, it should be understood that a plurality of shafts 108 may be employed.
As shown in
The plurality of holes 202 may extend partially or completely through each target plate 102. When the holes 202 are provided such that they only extend partially through each target plate 102, the separator plates 104 may be omitted. In such a case, an upper surface of a target plate 102 would directly contact a lower surface of an adjacent target plate 102. On the other hand, when the holes 202 are provided such that they extend completely through the target plates 102, the separator plates 104 are placed between the target plates 102 so as to separate the holes 202 of each target plates 102, thereby defining a plurality of individual compartments within each target plate 102 for holding one or more targets (e.g., seeds, wafers) therein.
The upper and lower surfaces of the target plate 102 may be polished so as to be relatively smooth and flat. The thickness of the target plate 102 may be varied to accommodate the targets to be contained therein. Although the target plate 102 is illustrated as being disc-shaped, it should be understood that the target plate 102 may have a triangular shape, a square shape, or other suitable shape. Additionally, it should be understood that the size and/or configuration of the holes 202 may be varied based on production requirements. Furthermore, although not shown, the target plate 102 may include one or more alignment markings on the side surface to assist with the orientation of the target plate 102 during the stacking step of assembling the target holding device 100.
It should be understood that a suitable coordinate system may differ from that shown in
The size of the targets 600 may be adjusted as appropriate for their intended use (e.g., radiography targets). For instance, a target 600 may have a length of about 3 mm and a diameter of about 0.5 mm. It should be understood that the size of the holes 202 and/or the thickness of the target plates 102 may be adjusted as needed to accommodate the targets 600. The targets 600 are strategically loaded in the appropriate holes 202 based on various factors (including the characteristics of each target material, known flux conditions of a reactor core, the desired activity of the resulting targets, etc.) so as to attain targets 600 having relatively uniform activity.
As shown in
Because the outer holes 202 will be closer to the flux when the target holding device 100 is placed in a reactor core, a greater number of targets 600 may be placed in each of the outer holes 202, thereby resulting in more equal activity amongst the targets 600 in the outer holes 202. On the other hand, fewer targets 600 may be placed in each of the inner holes 202 to offset the fact that these targets 600 will be farther from the flux, thereby allowing the targets 600 in the inner holes 202 to attain activity levels comparable to the targets 600 in the outer holes 202. Thus, the number of targets 600 in each hole 202 may be increased so as to decrease the resulting activity of each target in the hole 202. Conversely, the number of targets 600 in each hole 202 may be decreased so as to increase the resulting activity of each target in the hole 202.
It should be understood that
In another example, iridium (Ir) and gold (Au) seeds were loaded in a target plate 102 having holes 202 corresponding to the coordinate system illustrated in
The targets 600 may also be arranged based on cross-section, wherein cross-section (a) is the probability that an interaction will occur and is measured in barns. For instance, targets 600 formed of materials having lower cross-sections will have a lower probability that an interaction will occur compared to targets 600 formed of materials having higher cross-sections. As a result, targets 600 formed of materials having lower cross-sections may be arranged in holes 202 that will be in closer proximity to the flux during irradiation. With regard to
It should be understood that when a plurality of targets 600 of different materials are to be placed in the target holding device 100 for irradiation, the individual characteristics (e.g., neutron absorption rate) of each target 600 will be considered in conjunction with external factors (e.g., known flux conditions of the reactor core) when determining the proper arrangement within the target holding device 100. For instance, not only is the proper target plate 102 and hole 202 determined for a target 600 but also whether grouping is appropriate, and if so, the target(s) 600 that should be grouped together so as to attain targets 600 in the target holding device 100 having relative uniform activity.
After the target holding device 100 has been irradiated in the reactor core, a predetermined period of time may be allowed to pass before disassembling the target holding device 100 and collecting the targets 600. This waiting period may be beneficial by permitting any impurities in the target holding device 100 (as well as the targets 600 themselves) to sufficiently decay, thereby reducing or preventing the risk of harmful radiation exposure to personnel.
While a number of example embodiments have been disclosed herein, it should be understood that other variations may be possible. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
