Radiant energy – Supported for nonsignalling objects of irradiation
Reexamination Certificate
1999-09-14
2002-05-28
Anderson, Bruce (Department: 2878)
Radiant energy
Supported for nonsignalling objects of irradiation
C250S455110, C250S492300
Reexamination Certificate
active
06396065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a radioactive ray irradiating apparatus, and more particularly to a radioactive ray irradiating apparatus which can reliably carry out sterilization, pasteurization, termination of pests, and/or inhibition of germination by projecting radioactive rays.
2. Description of the Related Art
Radioactive ray irradiating apparatuses have been known for irradiating medical instruments, such as artificial dialyzers, syringe needles, surgical gloves, or medical containers, with radioactive rays for sterilizing such instruments prior to usage. Such apparatuses emit radioactive rays to a case in which medical instruments are stored. Since the density of the contents of the case is not uniform, it is difficult to determine the dose of radioactive rays at points in the case only by calculation. Therefore, it is necessary to irradiate the case with radioactive rays in advance to measure the actual dose of radioactive rays at points in the case, thereby determining a particular irradiating condition under which sterilization can be carried out reliably regardless of the arrangement of medical instruments stored in the case.
Specifically, this is done by providing a plurality of small radioactive ray sensors, such as film dosemeters sensitive to radioactive rays, at several points in the case together with the medical instruments, and then projecting the radioactive rays so that the sensors measure the actual dose values to determine appropriate irradiating conditions.
Radioactive rays are also used for treating diseases such as malignant tumors. In the treatment, lesions of malignant tumors or the like are irradiated with radioactive rays so that the tumor cells absorb the radiation energy and disappear. An apparatus called an X-ray CT (computed tomography) or images captured by this apparatus are used in the treatment for determining the irradiation field and conditions of radioactive rays. Specifically, the X-ray CT apparatus captures a sectional image of a patient and locates the tumor lesions, whereby the irradiation field and conditions are determined in a manner maximizing the amount of radioactive energy absorption of the tumor lesions and minimizing that of normal tissues.
Studies have been made in other industrial fields to use radioactive ray effects, especially the effect of imparting the energy of radioactive rays to cells. For instance, the FAO (Food and Agriculture Organization of the United Nations) and the CAC (the Secretariat of the Codex Alimentarius Commission) of the WHO (World Health Organization) have applied the irradiation of foods to other purposes, such as sterilization of putrefying bacteria or disease bacteria, termination of pests and parasites, germination control, or extension of food storage, and defined the standard dose for each application. Here, it is intended to realize the safe storage of food to thereby seek to find a solution to the food problem that is one of the most important issues of the world at moment.
Recently, the total abolition of using methyl bromide, which has been used for the termination of pests and parasites in the process of plant quarantine in Japan and many other countries, is under way. Since methyl bromide is an ozone layer destroying substance, it is a global trend to abolish the use and production of it, and the radioactive ray irradiation is considered as a promising candidate method for replacing methyl bromide. Examples of products imported to Japan to which plant quarantine is required are cut flowers, spices, crude drugs, fruits, grains, lumber, and many other types of products.
The conventional method described above for sterilizing medical instruments or the like that requires a preliminary procedure of determining the irradiating conditions using the radioactive ray sensors takes a lot of time due to repeated trial and error needed to find appropriate irradiating conditions. In particular, if the radioactive ray sensors formed by films or the like which cannot indicate measurement values real time are used, it may take quite a long time to determine the conditions. Such a problem may be allowed as long as the types of objects to be exposed are limited and the irradiation is repeated under the same conditions once the conditions are determined, as in the conventional irradiating method for medical instruments. However, when many kinds of objects to be exposed are provided and packed in a variety of styles, the complex condition determining procedure of the conventional method cannot be ignored.
In general, it is possible to project the radioactive rays having a sufficient strength necessary for sterilization to the objects to be exposed in the conventional irradiating method of medical instruments, because the objects to be exposed are not activated regardless of whether X-rays or gamma rays are used. Thus, what is important in determining the irradiating conditions is whether or not the sterilization is carried out sufficiently at a point indicating the minimum dose in the case, and it is not essentially a problem if there are some points indicating a particularly strong dose in the case. The uniform dose distribution is, therefore, not strictly required. However, if the objects to be exposed are food products or plants, radioactive rays will affect the objects themselves as well as the bacteria and pests to be sterilized which cling to the objects to be exposed. As a result of the excessive exposure to radioactive rays, taste, color, or smell, for example, of these objects may be changed by chemical reaction, causing unwanted events such as deterioration of food safety, lower nutrition of food, or flower death. Therefore, the irradiating conditions for these objects must be determined in such a manner that the objects are only made to suffer a limited amount of damage within an allowable range and that the purpose of irradiation such as sterilization can be carried out sufficiently. Generally, since there are not so many candidate conditions that meet the above requirements, the dose distribution has to be uniform in the irradiation area. Because of such additional requirements, it is more difficult to use the above trial-and-error type method to find irradiating conditions.
Meanwhile, the above-mentioned conventional radiotherapy system utilizes sectional images captured by the X-ray CT apparatus to identify a target irradiating area, and focuses the radioactive rays on the identified target area to determine the irradiating field and conditions so as to avoid irradiation of normal tissues as much as possible. Therefore, it is not possible to adopt this method without any modification for determining the irradiating conditions in the case that calls for the uniform dose distribution over the entire irradiating field.
SUMMARY OF THE INVENTION
The present invention is made to solve the above problems and aims to provide a radioactive ray irradiating apparatus capable of automatically determining irradiating conditions under which a uniform dose distribution is realized for the entire object to-be exposed, thereby saving time and cost taken for determining the irradiating conditions.
According to the present invention, a radioactive ray irradiating apparatus includes a tomographic image capturing means for imaging a sectional view of an object to be exposed along a direction of projecting radioactive rays to obtain a density distribution of the object to be exposed, and an irradiating condition determining means for determining irradiating conditions based on the density distribution of the object to be exposed so that the variation of the dose distribution of projected radioactive rays in the object to be exposed falls within a predetermined reference range. The apparatus projects the radioactive rays by controlling a radioactive ray irradiating means in accordance with the determined irradiating conditions.
In the radioactive ray irradiating apparatus according to the present invention, types of radioactive rays that can be p
Hirano Takeshi
Kimura Masakazu
Anderson Bruce
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
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