Patent Description:
In recent years, RI (radioisotope) drugs have come to be actively used in the medical field, for instance in the treatment of cancer (see for example PTL <NUM> and NPL <NUM> to <NUM>). Further, PTL <NUM> discloses a therapeutic agent and uses thereof and PTL <NUM> discloses a method for production of radioisotope preparations and their use in life science, research, medical application and industry.

For instance in RI therapeutic drugs administered for the purpose of treating cancer radiation emitted towards the exterior the body is very weak, and accordingly it is difficult to image the biodistribution of the RI therapeutic drugs through capture of radiation from outside the body. Therefore, means that have been tried to date for accurately grasping drug accumulation at a lesion site, so as to perform an appropriate treatment, include a first means, namely imaging of distribution upon administration of an RI drug for imaging, and a second means, namely imaging by capturing extremely weak radiation emitted from the RI therapeutic drug to the exterior of the body, using a high-sensitivity apparatus. In the first means, however, the biodistribution of the RI drug may vary when the radioisotope bound to a carrier varies, even for a same carrier; accordingly, distribution images obtained through administration of an RI drug for imaging are not necessarily identical to those of the distribution in the case of administration of an RI drug for treatment. In the second means, the ability of an apparatus for capturing and imaging, with high sensitivity, extremely weak radiation emitted from the RI therapeutic drug to the exterior of the body is not sufficient, and it thus difficult to obtain images of sufficiently high resolution.

Therefore, it is an object of the present invention to provide a technique that allows producing a novel radiolabeled compound.

In order to solve the above problem, the present invention strives to make it possible to produce a radiolabeled compound in which two or more radioisotopes are bound to a single carrier, through the use of two or more radioisotopes that are generated from an alloy of a target substance, by irradiating the alloy as a target substance with a radiation beam, and thereupon allowing the radioisotopes to migrate into a gas.

In further detail, the present invention is a method for producing a radiolabeled compound, the method including the steps of: irradiating an alloy as a target substance with a radiation beam, to generate two or more radioisotopes from the alloy, and allowing the two or more radioisotopes to migrate into a gas; generating an intermediate label by allowing a first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; and generating a final label by allowing a second radioisotope different from the first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with the intermediate label.

In the above producing method, an alloy as a target substance is irradiated with a radiation beam, and accordingly it becomes possible to generate two or more radioisotopes within a liquid target, and to generate a radiolabeled compound that is labeled with the two or more radioisotopes. In the above producing method, two or more radioisotopes can be generated simultaneously within a liquid target, through irradiation of the alloy as the target substance with a radiation beam; as a result, for instance the generated radioisotopes can bind quickly to a carrier, even in cases where the radioisotopes include a radioisotope of short half-life, and a radiolabeled compound can be generated that is labeled with the two or more radioisotopes.

In the present invention, the method for producing a radiolabeled compound may include the steps of: irradiating an alloy as a target substance with a radiation beam, to generate two or more radioisotopes from the alloy, and allowing the two or more radioisotopes to migrate into a gas; generating a first intermediate label by allowing a first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; generating a second intermediate label by allowing a second radioisotope different from the first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; and generating a final label by condensing the first intermediate label and the second intermediate label. Such a producing method as well allows generating a radiolabeled compound that is labeled with two or more radioisotopes.

The above method for producing a radiolabeled compound may further include a step of adjusting the temperature of the alloy so as to be a temperature at which both the first radioisotope and the second radioisotope evaporate, during irradiation with the radiation beam. In such a producing method at least two radioisotopes, namely a first radioisotope and a second radioisotope from among the multiple radioisotopes generated in the alloy, migrate into a gas, as a result of which the radioisotopes having migrated into the gas can be bound to a carrier.

The present invention can also be grasped from the aspect of a producing apparatus. For instance, the present invention may be an apparatus for producing a radiolabeled compound, the apparatus having: isotope generation means for irradiating an alloy as a target substance with a radiation beam, to generate two or more radioisotopes from the alloy, and allowing the two or more radioisotopes to migrate into a gas; a first generating unit which generates an intermediate label by allowing a first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; and a second generating unit which generates a final label by allowing a second radioisotope different from the first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with the intermediate label.

The present invention may have for instance isotope generation means for irradiating an alloy as a target substance with a radiation beam, to generate two or more radioisotopes from the alloy, and allowing the two or more radioisotopes to migrate into a gas; a third generating unit which generates a first intermediate label by allowing a first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; a fourth generating unit which generates a second intermediate label by allowing a second radioisotope different from the first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; and a fifth generating unit which generates a final label through condensation of the first intermediate label and the second intermediate label.

The present invention allows for producing for instance a radiolabeled compound wherein two or more radioisotopes generated from an alloy of a target substance through irradiation of the alloy with a radiation beam, are bound to a single carrier.

The present invention allows for producing for example a radiolabeled compound wherein astatine <NUM>At and iodine <NUM>I are bound to a single carrier.

The isotopes used in the present invention can be produced by an apparatus having: a first container which stores a target substance; a second container which receives a liquid transferred from the first container; a beam introduction portion which is a passage of the radiation beam, for irradiating a target substance with a radiation beam within the first container; and an extraction unit which extracts, from a gas, a radioisotope generated in the first container by the radiation beam and which migrates into the gas in the second container, wherein the second container and the extraction unit are hermetically connected to each other so that the gas that contains the radioisotope is conducted therebetween.

The present invention allows producing a novel radiolabeled compound.

Embodiments of the invention of the present application will be explained next. The embodiments illustrated below are implementations of the present invention and are not meant to limit the technical scope of the invention of the present application.

<FIG> is a diagram illustrating an example of a radiolabeled compound producing apparatus. The radiolabeled compound producing apparatus <NUM> is an apparatus in which an alloy as a target substance is irradiated with a radiation beam, to generate two or more radioisotopes, from the alloy, that are then allowed to migrate into a gas, whereupon the radioisotopes are combined with a label precursor. Accordingly, the radiolabeled compound producing apparatus <NUM> is provided with a radioisotope producing apparatus <NUM> that generates radioisotope and causes the radioisotopes to migrate into a gas, and a synthesis apparatus <NUM> which generates a chimera RI molecule by allowing the radioisotopes to react with a label precursor. In the present application the term chimera RI denotes a molecule resulting from binding of two or more radioisotopes to one molecule.

The term alloy denotes herein a mixture of two or more types of metals, the mixture being preferably at least solid or liquid at the temperature of the space in which the radioisotope producing apparatus <NUM> is installed. The term label precursor denotes for instance a substance, in an RI therapeutic drug, to which the radioisotopes are bound, and that is used as a carrier for transporting the radioisotope into the body.

<FIG> illustrates irradiation of an alloy of bismuth Bi and antimony Sb with a radiation beam to generate, from the alloy, astatine <NUM>At and iodine <NUM>I that are then allowed to migrate into a gas, whereupon the astatine <NUM>At and the iodine <NUM>I are allowed to react with a label precursor, to thereby generate a final label in the form of a chimera RI molecule. In the radiolabeled compound producing apparatus <NUM> of the present embodiment, two or more radioisotopes are generated simultaneously in the radioisotope producing apparatus <NUM> by one radiation beam, and the generated radioisotopes move at once into the synthesis apparatus <NUM> and are allowed to react with a label precursor. Accordingly, the radiolabeled compound producing apparatus <NUM> is suitable for synthesis of for instance a chimera RI molecule in which two or more halogen-based radioisotopes such as astatine <NUM>At and iodine <NUM>I are allowed to react with a label precursor. However, the radiolabeled compound producing apparatus <NUM> is not limited to generating such radiolabeled compounds.

<FIG> is a diagram illustrating an example of the radioisotope producing apparatus <NUM>. The radioisotope producing apparatus <NUM> is provided with a crucible <NUM> that holds an alloy of a target substance, a heater <NUM> that heats up the alloy in the crucible <NUM>, a beam port <NUM> for projecting a radiation beam to the alloy in the crucible <NUM>, a gas introduction port <NUM> for introducing gas into the crucible <NUM>, and a gas lead-out port <NUM> for leading, out of the crucible <NUM>, the gas that is to be fed to the synthesis apparatus <NUM>. Beam windows <NUM>, <NUM> are provided in the beam port <NUM>. A jacket <NUM> is provided with the crucible <NUM>.

The crucible <NUM> is a container for storing, in the interior thereof, a target substance, and for melting at least part of the target-constituting substance. Preferably, the target substance is melted into a liquid, in the crucible <NUM>. Accordingly, the crucible <NUM> is required to be at least heat-resistant enough to withstand a temperature of the melting point of the target substance. Therefore, for instance quartz, ceramics, metals and the like are suitably used as the material of such a crucible <NUM>. The crucible <NUM> is sealed, and open portions other than the gas introduction port <NUM> and the gas lead-out port <NUM> are closed, at the time of irradiating with the radiation beam.

The heater <NUM> is a heating means for heating the interior of the crucible <NUM>. The heater <NUM> heats up the interior of the crucible <NUM>, to thereby heat up the target substance stored in the crucible <NUM>. As a result, melting of the target substance is promoted, and part or the entirety of the target substance can be melted and liquefied. Various heating means, such as a micro sheath heater and others can be used as such a heater <NUM>. During irradiating with the radiation beam, the irradiated portion generates heat on account of the energy from the radiation beam, and hence heating by the heater <NUM> may be unnecessary in some instances.

The jacket <NUM> is a cooling space disposed around the crucible <NUM>. An inlet and an outlet of a coolant for cooling the crucible <NUM> are provided with the jacket <NUM>, such that the jacket <NUM> can be cooled through introduction of the coolant into the jacket <NUM> via the inlet. Also, natural heat dissipation elicited through discontinuation of heating by the heater <NUM> can be expected to result in cooling of the crucible <NUM>. The crucible <NUM> can however be cooled more quickly through introduction of a coolant into the jacket <NUM>. Examples of the coolant that is introduced into the jacket <NUM> include for instance air in the room in which the radiolabeled compound producing apparatus <NUM> is installed, or a gas such as nitrogen gas, or liquid such as water, prepared for the purpose of cooling of the crucible <NUM>. The manner in which the crucible <NUM> is cooled may involve for instance allowing a coolant to flow thus in the jacket <NUM>; or alternatively, providing cooling fins on the surface of the crucible <NUM>, or providing a thermoelectric conversion element such a Peltier element.

The beam port <NUM> is a tubular part running through a side wall portion of the crucible <NUM>, and which forms a passage for allowing a radiation beam, outputted from a radiation beam generator disposed in the vicinity of the crucible <NUM>, to strike into the crucible <NUM>. Accordingly, the target substance stored in the crucible <NUM> is disposed on an extension line of the passage of the beam port <NUM>. Both ends of the passage formed by the beam port <NUM> are closed by the beam windows <NUM>, <NUM>, in order to ensure the sealability of the crucible <NUM>. The beam windows <NUM>, <NUM> are for instance made up of a metal plate that lets radiation beams through but are not melted by the radiation beams. The interior of the beam port <NUM> is evacuated or is filled with a gas (for instance He gas). The radiation beam outputted from the radiation beam generator passes through the beam window <NUM>, the interior of the beam port <NUM> and the beam window <NUM> and reaches the target substance in the crucible <NUM>.

The gas introduction port <NUM> is an inlet through which a gas is introduced into the crucible <NUM>. The gas lead-out port <NUM> is an outlet for discharging a gas from a gas phase portion of the crucible <NUM>. The gas introduction port <NUM> and the gas lead-out port <NUM> are for instance tubular pipes. The gas introduction port <NUM> allows a gas to flow into and out the crucible <NUM>. A gas for recovery of radioisotopes is introduced through the gas introduction port <NUM>. For instance, He gas that is not radioactivated by radiation beams is suitably used as the gas that is introduced into the crucible <NUM>. The gas is introduced through the gas introduction port <NUM>, as a result of which the gas is discharged from the gas lead-out port <NUM>. In consequence, this elicits flow of gas from the gas introduction port <NUM> towards the gas lead-out port <NUM>, in the gas phase portion in the crucible <NUM>. As a result of such gas flow, it becomes possible to discharge, via the gas lead-out port <NUM>, radioisotopes that are generated in the target substance through irradiation with a radiation beam and that migrate into the gas in the gas phase portion. The flow rate of the gas discharged out of the gas lead-out port <NUM> and pressure in the crucible <NUM> can be adjusted by adjusting the flow rate of the gas that is introduced into the crucible <NUM> through the gas introduction port <NUM>, and/or by adjusting the degree of opening of a flow rate adjustment valve that is provided in the vicinity of the gas lead-out port <NUM>.

<FIG> is a diagram illustrating an example of the synthesis apparatus <NUM>. The synthesis apparatus <NUM> has two columns for allowing radioisotopes to react with a label precursor, namely a first column <NUM> through which the gas discharged from the gas lead-out port <NUM> of the radioisotope producing apparatus <NUM> passes, and a second column <NUM> through which gas having passed through the first column <NUM> passes. The first column <NUM> selectively captures a first radioisotope from among the two or more radioisotopes generated from the alloy of the target substance in the crucible <NUM> of the radioisotope producing apparatus <NUM>, to perform an RI labeling reaction of allowing the first radioisotope to react with the label precursor. In the first column <NUM>, therefore, the first radioisotope from among the two or more radioisotopes contained in the gas discharged from the gas lead-out port <NUM> of the radioisotope producing apparatus <NUM> is used in an RI labeling reaction, while the second radioisotope passes as-is through the first column <NUM>. At this stage the label precursor having the first radioisotope bound thereto in the first column <NUM> is one type of intermediate label, as referred to in the present application, since this label precursor precedes binding of the second radioisotope in the second column <NUM>. Specifically, the term intermediate label in the present application denotes a label having bound thereto at least either one of the two or more radioisotopes that are to be bound, at a time prior to completion of binding all of the two or more radioisotopes.

In the second column <NUM> on the downstream side of the first column <NUM>, the second radioisotope having passed through the first column <NUM> is captured; the second radioisotope is allowed to react with the intermediate label having been labeled in the first column <NUM>, to generate a final label as a result. Schemes conforming to the compound to be synthesized are utilized in the first column <NUM> and the second column <NUM>. For instance, a batch method is used in a case where reaction time is long, whereas a flow method is used in a case where reaction time is short.

A normally RI labeling reaction is carried out in the first column <NUM>. In a case for instance where an RI labeling reaction by astatine <NUM>At is carried out in the first column <NUM>, an electrophilic substitution reaction, a nucleophilic substitution reaction, an electrophilic addition reaction or a radical reaction may be resorted to as a halogenation reaction that can be utilized in the first column <NUM>. In order to bind a radioactive halogen such as astatine <NUM>At to for instance a peptide, which is a type of carrier, firstly a peptide compound, synthesized on site or procured commercially, is prepared and is bound to a carrier within the first column <NUM>, after which astatine <NUM>At is bound to the peptide, at an appropriate reaction temperature and during an appropriate reaction time, while under the concomitant use of an appropriate amount of an oxidant and/or a solvent.

The first column <NUM> is made up of devices conforming to various labeling methods. In an on-column labeling method, for instance, the first column <NUM> is made up of a solid-phase column that holds a reaction solution, and tubing for allowing the label precursor to pass through the solid-phase column.

In the second column <NUM> as well an RI labeling reaction is carried out. In the second column <NUM> the radioisotope having passed through the first column <NUM> is allowed to react with the intermediate label, having been labeled in the first column <NUM> and having been transferred from the first column <NUM> to the second column <NUM>, so that a final label is generated as a result. In a case for instance where astatine <NUM>At is bound to a peptide in the first column <NUM>, as described above, the peptide having astatine <NUM>At bound thereto corresponds herein to the intermediate label. Also in the second column <NUM>, a halogenation reaction such as an electrophilic substitution reaction, a nucleophilic substitution reaction, an electrophilic addition reaction or a radical reaction can be utilized, similarly to the first column <NUM>. However, the amount of the intermediate label having been labeled in the first column <NUM> and supplied to the second column <NUM> is very small, at most of several tens of pmol; accordingly, a very small space is formed in the second column <NUM>, so as to enable a pico-scale RI labeling reaction to be carried out. The intermediate label generated in the first column <NUM> is transferred to the second column <NUM>, together with the radioisotope that passes through the first column <NUM>, as a result of unbinding of the intermediate label from the carrier in the first column <NUM>. The method for separating the intermediate label from the carrier in the first column <NUM> depends on the binding method, but may involve for instance natural separation from the carrier accompanying binding to the radioisotope, or may be a method in which an eluent containing an additive that unbinds the intermediate label from the carrier in the first column <NUM> is injected. The intermediate label transferred to the second column <NUM> is bound to a carrier of the second column, within a very small space; the radioisotope having passed through the first column <NUM> becomes then bound to the intermediate label that is in turn bound to the carrier of the second column. In a case for instance where astatine <NUM>At and iodine <NUM>I are fed from the radioisotope producing apparatus <NUM> to the synthesis apparatus <NUM> by a gas, as described above, then iodine <NUM>I having passed through the first column <NUM> becomes bound to the intermediate label in the second column <NUM>.

Various automation techniques that allow for quick and efficient synthesis are preferably utilized in the synthesis apparatus <NUM>, in order to enable efficient synthesis of a label having a short half-life, such as astatine <NUM>At, as described above.

<FIG> is an example of a process flow performed in the radiolabeled compound producing apparatus <NUM>. Hereafter, the process flow performed in the radiolabeled compound producing apparatus <NUM> will be explained with reference to the flowchart of <FIG>.

In the case of generation of a radiolabeled compound using the radiolabeled compound producing apparatus <NUM>, a substance conforming to the label type is placed with the crucible <NUM> of the radioisotope producing apparatus <NUM>, and a gas is injected through the gas introduction port <NUM> at an appropriate flow rate. The crucible <NUM> is heated through energization of the heater <NUM> (S101). The target substance in the crucible <NUM> melts when reaching the melting point, and becomes a liquid alloy of the target substance, in the crucible <NUM>. For instance, alloys of bismuth Bi and antimony Sb have a melting point of about <NUM> to <NUM>, depending on the alloy ratio; accordingly, the interior of the crucible <NUM> is preferably brought to a temperature that is at least higher than the melting points of bismuth Bi and antimony Sb, in a case where these are placed in the crucible <NUM>. The alloy ratio is established herein as appropriate taking into consideration for instance the type and structure of the RI drug to be produced, the proportion in which radioactive compounds generated by the radioisotope producing apparatus <NUM> move into the synthesis apparatus <NUM>, and labeling ratios and reaction times in the first column <NUM> and the second column <NUM>.

Next, the interior of the crucible <NUM> is irradiated with a radiation beam via the beam port <NUM> (S102). Examples of radiation beams that irradiates the interior of the crucible <NUM> include α-beams (<NUM>He<NUM>+), <NUM>He<NUM>+, <NUM>H+, <NUM>H+, <NUM>Li<NUM>+ and the like. The radiation beams utilized are <NUM>H+, <NUM>H+, <NUM>He<NUM>+, <NUM>He<NUM>+ or <NUM>Li<NUM>+ in a case where target-constituting substance is an element of group <NUM>, group <NUM>, group <NUM> or group <NUM>. In consequence, the main radioisotopes generated as a result of a nuclear reaction between the target-constituting substance and the radiation beam are elements of group <NUM>, group <NUM>, group <NUM> and group <NUM>. In a case where an alloy of bismuth Bi and antimony Sb are stored in the crucible <NUM>, irradiation with α-beams into the crucible <NUM> results in generation of astatine <NUM>At and iodine <NUM>I as radioisotopes, since both bismuth Bi and antimony Sb are group <NUM> elements.

When the interior of the crucible <NUM> is irradiated with a radiation beam, at least two radioisotopes become generated in the liquid phase portion of the crucible <NUM>. The multiple radioisotopes generated in the crucible <NUM> ordinarily have mutually different boiling points. For instance, astatine <NUM>At has a boiling point of <NUM> at normal pressure (<NUM> atmosphere). The boiling point at normal pressure of iodine <NUM>I is however <NUM>. In the radiolabeled compound producing apparatus <NUM> a configuration is adopted wherein the multiple radioisotopes generated in the crucible <NUM> and having migrated from the liquid phase portion into the gas in the gas phase portion are fed to the synthesis apparatus <NUM>; accordingly, the multiple radioisotopes generated in the crucible <NUM> must all evaporate in the crucible <NUM> and migrate from the liquid phase portion into the gas in the gas phase portion. In the radiolabeled compound producing apparatus <NUM> of the present embodiment, therefore, the temperature in the interior of the crucible <NUM> is adjusted, for instance by the heater <NUM>, so as to be higher than the boiling point of at least the radioisotope of highest boiling point from among the multiple radioisotopes that are to be fed to the synthesis apparatus <NUM>. The temperature in the interior of the <NUM> is adjusted for instance to be <NUM> or higher, although depending on the pressure in the crucible <NUM>, in a case for instance where both astatine <NUM>At and iodine <NUM>I are allowed to evaporate in the crucible <NUM> and migrate from the liquid phase portion into the gas in the gas phase portion. The boiling point of bismuth Bi is <NUM> and the boiling point of antimony Sb is <NUM>. The boiling point of alloys of bismuth Bi and antimony Sb is about <NUM> to <NUM>, depending on the alloy ratio; accordingly, a liquid alloy which is the target substance does not evaporate so long as the interior of the crucible <NUM> is kept at a temperature lower than that.

The radioisotopes that evaporate from in the crucible <NUM> and move from the liquid phase portion in the crucible <NUM> into the gas in the gas phase portion flow out of the crucible <NUM>, and into the synthesis apparatus <NUM>, together with He gas that flows from the gas introduction port <NUM>, through the interior of the crucible <NUM>, and towards the gas lead-out port <NUM>. In the first column <NUM> of the synthesis apparatus <NUM> the first radioisotope, from among the two or more radioisotopes contained in the He gas that flows from the radioisotope producing apparatus <NUM> towards the synthesis apparatus <NUM>, becomes bound to a label precursor, to generate an intermediate label. In the second column <NUM> of the synthesis apparatus <NUM>, the second radioisotope having passed through the first column <NUM>, from among the two or more radioisotopes contained in the He gas that flows from the radioisotope producing apparatus <NUM> towards the synthesis apparatus <NUM>, becomes bound to the intermediate label, and a final label is generated thereupon.

In a case for instance where an alloy of bismuth Bi and antimony Sb is stored as a target substance in the crucible <NUM>, and astatine <NUM>At and iodine <NUM>I generated in the crucible <NUM> as a result of irradiation with α-beams flow from the radioisotope producing apparatus <NUM> into the synthesis apparatus <NUM>, then an intermediate label in which astatine <NUM>At is bound to a label precursor is generated in the first column <NUM>, and a final label, in which iodine <NUM>I is further bound to the intermediate label, is generated in the second column <NUM>.

In the radiolabeled compound producing apparatus <NUM> of the embodiments, thus, an alloy serves as the target substance, and accordingly two or more types of objective radioisotopes can be generated simultaneously within a liquid target, and a radiolabeled compound that is labeled with two or more radioisotopes can likewise be generated, through irradiation of the alloy as the target substance with a same radiation beam. The radiolabeled compound thus labeled with two or more radioisotopes can be used for instance in the manner described below.

<FIG> is an image diagram illustrating cancer treatment and diagnosis. For instance, astatine <NUM>At having received attention in recent years as an α ray emitting nuclide for cancer treatment emits herein α-ray capable of selectively destroying cancer cells alone, since the range of astatine <NUM>At within the body is short. However, images of an RI drug taken up by cancer cells are indistinct, and insufficient for clinical use, as depicted by the "image" in the comparative example section of <FIG>, due for instance to sensitivity and resolution problems that arise when attempting to capture human biodistribution of an RI drug labeled with astatine <NUM>At, which has a short half-life of about <NUM> hours, by single photon emission computed tomography (SPECT) or using a Compton camera, both techniques being sensitive to X-rays and gamma rays radiated by astatine <NUM>At. By contrast, iodine <NUM>I has a comparatively long half-life of about <NUM> days, and accordingly the human biodistribution of an RI drug labeled with iodine <NUM>I can be captured by a positron emission tomographic (PET) apparatus for positron emission tomography, which is an imaging technique relying on positron detection; as depicted by the "image" in the working example section of <FIG>; an image of an RI drug taken up by cancer cells is clearly reflected in this case, and can be sufficiently used in a clinical setting.

For instance as reported by D. Scott Wilbur et al. in NPL <NUM> above, the biodistribution of the RI drug having astatine <NUM>At bound thereto are not identical to the biodistribution of an RI drug having iodine <NUM>I bound thereto, even for a same label precursor. In conventional art it is therefore necessary to address differences in the distribution of both drugs where laying out a cancer treatment plan. In this regard, the radiolabeled compound producing apparatus <NUM> of the above embodiment allows two radioisotopes, namely astatine <NUM>At and iodine <NUM>I, to be bound to a single carrier, and accordingly allows finely imaging, by means of a PET apparatus, the distribution of an RI drug administered for the purpose of treating cancer. Herein a radiolabeled compound that may be grasped under the appellation of "chimera RI drug" can be used as an RI drug that fulfills two functions, namely a therapeutic function and an imaging function, through binding of two radioisotopes, i.e. astatine <NUM>At and iodine <NUM>I having different natures, to a single carrier, despite the fact the radiolabeled compound is labeled with astatine <NUM>At having a comparatively short half-life. The feasibility of using such a chimera RI drug derives from the fact that the radiolabeled compound is produced using the radiolabeled compound producing apparatus <NUM> of the above embodiment, which allows generating simultaneously two or more radioisotopes through irradiation of an alloy as a target substance with a radiation beam, and allows binding the two or more radioisotopes to a label precursor in a short time. Such a chimera RI drug cannot be produced, on account of time constraints, in conventional producing methods that involve, for instance, irradiating a solid target with a radiation beam, and extracting a radioisotope, generated within the solid target, for instance by dry distillation.

In the configuration of the radiolabeled compound producing apparatus <NUM> of the above embodiment, the first column <NUM> and the second column <NUM> of the synthesis apparatus <NUM> are disposed in series, such that the gas discharged from the gas lead-out port <NUM> of the radioisotope producing apparatus <NUM> follows a path leading through the first column <NUM>, after which the gas flows to the second column <NUM>. However, the first column <NUM> and the second column <NUM> in the radiolabeled compound producing apparatus <NUM> may be disposed in parallel.

<FIG> is a diagram illustrating a first variation of the radiolabeled compound producing apparatus <NUM>. In the radiolabeled compound producing apparatus <NUM> of the above embodiment, a configuration may be adopted wherein the columns in which the radioisotopes become bound to the label precursor are provided as two columns in parallel, such that the gas discharged from the gas lead-out port <NUM> of the radioisotope producing apparatus <NUM> flows in parallel in the two columns, as illustrated in <FIG>. In that case two or more radioisotopes generated from the alloy of a target substance in the crucible <NUM> of the radioisotope producing apparatus <NUM> flows in the two columns in the synthesis apparatus <NUM>. Therefore, in one of the two columns of the synthesis apparatus <NUM> in the case of the present first variation an RI labeling reaction is carried out in which a first radioisotope, from among the two or more radioisotopes generated from the alloy of the target substance in the crucible <NUM> of the radioisotope producing apparatus <NUM>, is selectively captured, and is allowed to react with a label precursor, to generate a first intermediate label. In the other of the two columns of the synthesis apparatus <NUM> an RI labeling reaction is carried out in which a second radioisotope different from the first radioisotope, from among the two or more radioisotopes generated from the alloy of the type the target substance in the crucible <NUM> of the radioisotope producing apparatus <NUM> is selectively captured, and is allowed to react with the label precursor, to generate a second intermediate label. The first intermediate label and the second intermediate label generated in the respective columns are then condensed, to generate a final label.

In a case for instance where an RI drug of astatine <NUM>At and iodine <NUM>I such as the one exemplified in the above embodiment is produced in accordance with the present first variation, an RI labeling reaction of allowing astatine <NUM>At to react with a label precursor is performed in one of the two columns of the synthesis apparatus <NUM>. An RI labeling reaction of allowing iodine <NUM>I to react with a label precursor is carried out in the other of the two columns of the synthesis apparatus <NUM>. For instance, any one from among an electrophilic substitution reaction, a nucleophilic substitution reaction, an electrophilic addition reaction and a radical reaction can be resorted to in the column where astatine <NUM>At is allowed to react with the label precursor, but an electrophilic substitution reaction is most suitable herein. Meanwhile, for instance any one from among an electrophilic substitution reaction, a nucleophilic substitution reaction, an electrophilic addition reaction, a nucleophilic addition reaction and a radical reaction may be resorted to in the column in which iodine <NUM>I is allowed to react with a label precursor; preferred herein are however an electrophilic substitution reaction, a nucleophilic substitution reaction and an electrophilic addition reaction, and a radical reaction as a next preferred reaction.

The intermediate label of astatine <NUM>At and the intermediate label of iodine <NUM>I respectively generated in the two columns of the synthesis apparatus <NUM> are debound from the carrier in each column, are retrieved, and are condensed in another column. In the column in which condensation is carried out, a very small space for pico-scale condensation is formed, similarly to the above-described second column <NUM>, since the intermediate labels are condensed with each other in the pico-scale. Upon condensation of the intermediate label of astatine <NUM>At and the intermediate label of iodine <NUM>I a final label becomes perfected in the form of a chimera RI drug in which two radioisotopes, namely astatine <NUM>At and iodine <NUM>I are bound to a single carrier.

In the present first variation as well, similarly to the above embodiment, two or more radioisotopes can be generated simultaneously within a liquid target, and a radiolabeled compound that is labeled with the two or more radioisotopes can be generated, through irradiation of an alloy as the target substance with a radiation beam. Thus, a radiolabeled compound having been thus labeled with two or more radioisotopes can be used as an RI drug that delivers both a therapeutic function and an imaging function, as described above.

In the above embodiment an implementation is adopted in which the radioisotopes generated in the liquid phase portion of the crucible <NUM> flow into the synthesis apparatus <NUM> from the gas phase portion of the crucible <NUM>, but the radiolabeled compound producing apparatus <NUM> of the above embodiment is not limited to such a configuration.

<FIG> is a diagram illustrating a variation of a radioisotope producing apparatus. In the present modification, constituent elements identical to those in the above embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted. A radioisotope producing apparatus 2A according to the present variation has a configuration wherein the crucible <NUM> according to the above embodiment is herein separated into a target container 21A and a storage container 21B. Similarly to the crucible <NUM> according to the above embodiment, the target container 21A is provided with a heater 22A that heats up an alloy within the target container 21A, a beam port <NUM> for irradiating an alloy within the target container 21A with a radiation beam, and a gas introduction port 24A for introducing a gas into the crucible <NUM>. Beam windows <NUM>, <NUM> are provided in the beam port <NUM>. A jacket <NUM> is provided in the target container 21A.

The target container 21A is a container for storing, in the interior thereof, a target-constituting substance, and for melting at least part of the target substance. Similarly to the crucible <NUM>, the target container 21A is heat-resistant so as to be capable of withstanding the temperature of the melting point of target-constituting substance. A transfer pipe <NUM> for transfer of a liquid alloy from the interior of the target container 21A towards the storage container 21B is connected to the bottom of the target container 21A.

The storage container 21B is a storage container that receives the liquid alloy transferred from the target container 21A. Similarly to the target container 21A, the storage container 21B has heat resistance that allows withstanding the temperature of the melting point of the liquid alloy transferred from the target container 21A. An opening at the end of a transfer pipe <NUM> is disposed in the vicinity of the bottom of the storage container 21B, so that the liquid alloy flowing through the transfer pipe <NUM> flows out into the storage container 21B at the liquid phase portion of the storage container 21B. The storage container 21B is provided with a heater 22B for heating the alloy within the storage container 21B, a gas introduction port 24B for feeding a gas into the gas phase portion of the storage container 21B, and a gas lead-out port <NUM> for feeding gas from the gas phase portion of the storage container 21B to the synthesis apparatus <NUM>. The storage container 21B also functions as a heating container for heating the liquid alloy transferred from the target container 21A.

The explanation in <FIG> deals with an example of a configuration wherein the gas lead-out port <NUM> that is connected to the synthesis apparatus <NUM> is not provided in the target container 21A, but this implementation is not limiting. A gas lead-out port <NUM> connected to the synthesis apparatus <NUM> may be provided in the target container 21A.

The heater 22A and the heater 22B in the radioisotope producing apparatus 2A according to the present variation can be controlled as follows. As described above, the boiling point of for instance astatine <NUM>At at normal pressure (<NUM> atmosphere) is <NUM>, and the boiling point of iodine <NUM>I at normal pressure is <NUM>; hence, it was necessary to adjust the temperature in the interior of the crucible <NUM> for instance to be <NUM> or higher, in order to allow both astatine <NUM>At and iodine <NUM>I to evaporate in the radioisotope producing apparatus <NUM> of the above embodiment, and allow astatine <NUM>At and iodine <NUM>I to migrate from the liquid phase portion into the gas in the gas phase portion. In the radioisotope producing apparatus 2A according to the present variation, however, a configuration is adopted in which the liquid alloy in the target container 21A is transferred to the storage container 21B, and accordingly astatine <NUM>At and iodine <NUM>I can be allowed to evaporate within the storage container 21B, and allowed to migrate from the liquid phase portion into the gas in the gas phase portion, by bringing the storage container 21B to <NUM> or above by means of the heater 22B. That is, the temperature in the target container 21A can be adjusted to a temperature lower than <NUM>. In a case where the beam windows <NUM>, <NUM> cannot withstand a temperature of <NUM> or higher, the present variation allows therefore astatine <NUM>At and iodine <NUM>I to migrate into the gas in the gas phase portion, even if the target container 21A is brought to the heat resistance temperature of the beam windows <NUM>, <NUM>.

<FIG> is a diagram illustrating a second variation of the radioisotope producing apparatus. In a radiolabeled compound producing apparatus 1A according to the present second variation, an alloy as a target substance within the target container 21A is irradiated with a radiation beam, to generate two or more radioisotopes in the alloy, whereupon the alloy that has given rise to the radioisotopes is transferred to the storage container 21B, the radioisotopes migrate into a gas in the storage container 21B, and the radioisotopes are combined with a label precursor in the synthesis apparatus <NUM>.

Also in the radiolabeled compound producing apparatus 1A of the present second variation, an alloy serves as the target substance, as in the radiolabeled compound producing apparatus <NUM> of the above embodiment. Accordingly, two or more types of objective radioisotopes can be generated simultaneously within a liquid target, and a radiolabeled compound that is labeled with two or more types of radioisotopes can be generated, through irradiation of the alloy as the target substance with a same radiation beam.

In the above embodiment and the first and second variations, examples of a radiolabeled compound have been illustrated in the form of an RI drug labeled with astatine <NUM>At and iodine <NUM>I, through irradiation of an alloy of bismuth Bi and antimony Sb with a radiation beam. However, the above embodiment and variations are not limited to such an implementation. The radiolabeled compound produced in the radiolabeled compound producing apparatus <NUM> may result from incorporating for instance sulfur S, gallium Ga, selenium Se, tin Sn, tellurium Te, lead Pb or the like into a target substance, to thereby generate various radioisotopes of chlorine Cl, arsenic As, bromine Br or the like that are then bound to a single carrier.

The radioisotope producing apparatus 2A in the above variation can be used for instance by being replaced by a crucible according to the embodiment described below.

<FIG> is a diagram illustrating a configuration example of a radioisotope producing apparatus of the present second embodiment. A radioisotope producing apparatus <NUM> has a crucible <NUM>, a heater <NUM>, a jacket <NUM>, a beam port <NUM>, a beam window <NUM>, a beam window <NUM>, an inlet <NUM>, an outlet <NUM> and a trap <NUM>.

The crucible <NUM> is a heat-resistant container in which a substance that constitutes a target (for instance bismuth) is melted. The crucible <NUM> is a storage container that stores a target-constituting substance. For instance, quartz, a ceramic or a metal is used as the crucible <NUM>. The crucible <NUM> is required to be at least heat-resistant enough to withstand a temperature of the melting point of the target-constituting substance. The crucible <NUM> is sealed, but a gas can be led into and out of the crucible <NUM> via the inlet <NUM> and the outlet <NUM>. A beam port <NUM> is connected to the crucible <NUM>. The crucible <NUM> is an example of a heat-resistant container.

The heater <NUM> is a heating means for heating the crucible <NUM>. The heater <NUM> heats the crucible <NUM> up, to thereby heat up the target-constituting substance in the crucible <NUM>. This allows promoting melting of the target substance. The target substance is typically melted and liquefied. For instance, a micro sheath heater is used as the heater <NUM>. The heater <NUM> is not limited to a micro sheath heater. Further, the target-constituting substance in the crucible <NUM> need not liquefy entirely. That is, part of the target-constituting substance may remain as a solid. The target-constituting substance liquefies when heated by the heater <NUM>. In the interior of the crucible <NUM>, there is a liquid phase by the liquefied substance, and a gas phase from a gas or the like that is introduced from the inlet <NUM>. The heater <NUM> is an example of a heating unit.

Herein an instance is exemplified in which a target substance is heated by the heater <NUM>, and the substance is liquefied, but the heating means is not limited thereto. For instance, the rise in temperature that is elicited in a beam irradiation portion upon irradiation of the target substance with a radiation beam (rise in temperature derived from heat from a nuclear reaction) can also be exploited herein. A combination of two or more conventionally known heating means can also be used, for instance heating by the heater <NUM>, and warming derived from irradiation with the radiation beam.

The jacket <NUM> is a cooling space disposed around the crucible <NUM>. An inlet and an outlet for a coolant (for instance air) are provided in the jacket <NUM>, such that the crucible <NUM> is cooled through introduction of the coolant into the jacket <NUM> via the inlet. Cooling can be accomplished by discontinuing heating by the heater <NUM>, or more quickly through introduction of the coolant into the jacket <NUM>. The coolant introduced into the jacket <NUM> is not limited to air (for instance air at normal temperature), and may be another gas such as nitrogen, or a liquid such as water.

And instance where the crucible <NUM> is cooled through introduction of a coolant into the jacket <NUM> is explained herein as an example of a cooling method of the crucible <NUM>, but the cooling method is not limited thereto, and a combination of one, two or more conventionally known cooling means can be resorted to. For instance, an element such as a Peltier element can be used herein.

The beam port <NUM> is a passage for introduction of the radiation beam that irradiates the target-constituting substance in the crucible <NUM>. The interior of the beam port <NUM> is evacuated or has a gas (for instance He gas) introduced thereinto. The beam port <NUM> has a tubular shape both ends of which are plugged by the beam window <NUM> and the beam window <NUM>. The beam window <NUM> is connected to a radiation beam generator such as an accelerator. The beam window <NUM> and the beam window <NUM> are, for instance, metal plates. A radiation beam accelerated by an accelerator or the like included in the radiation beam generator enters the beam port <NUM> from the beam window <NUM>, passes through the beam window <NUM>, and strikes into the crucible <NUM>. The target (typically a liquefied liquid target) is irradiated in this manner. The beam window <NUM> and the beam window <NUM> are substances through which at least part of the radiation beam can pass. The beam window <NUM> is a substance that does not melt even at the temperature of the liquid target in the interior of the crucible <NUM>. The beam port <NUM>, the beam window <NUM> and the beam window <NUM> are examples of beam introduction portions.

The inlet <NUM> is an inlet through which a gas is introduced into the crucible <NUM>. The inlet <NUM> is for instance a tubular pipe. The inlet <NUM> connects the interior and the exterior of the crucible <NUM>, so that a gas can be led into/out of the crucible <NUM>. A gas for recovery of radioisotopes is introduced through the inlet <NUM>. The gas which can be preferably used includes a gas that does not liquefy or solidify through cooling by the below-described trap <NUM>. The above gas is for instance He gas. The gas is introduced through the inlet <NUM> and is discharged as a result from the outlet <NUM>. In consequence, this elicits flow of gas from the inlet <NUM> towards the outlet <NUM>, in the gas phase in the crucible <NUM>. As a result of such gas flow it becomes possible to convey, towards the outlet, the radioisotopes having migrated into the gas phase. The amount of gas discharged from the outlet <NUM> can be adjusted through adjustment of the amount of gas introduced through the inlet <NUM>. The pressure of the gas phase in the crucible <NUM> can be controlled for instance through adjustment of the amount of gas that is introduced, for example by adjusting the amount of gas that is discharged from the outlet <NUM> (for instance by reducing the flow rate of the gate, and typically plugging the outlet <NUM>), or by plugging the discharge side of the trap <NUM>. The pressure of the gas phase in the crucible <NUM> can be controlled, with yet higher precision, by combining adjustment of the amount of gas discharged from the outlet <NUM> or adjustment of the amount of gas discharged from the discharge side of the trap <NUM>, with adjustment of amount of gas that is introduced through the inlet <NUM>.

The outlet <NUM> is an outlet through which gas from the crucible <NUM> is discharged. The outlet <NUM> is, for instance, a tubular pipe. The outlet <NUM> connects the interior of the crucible <NUM> and the trap <NUM>, so that a gas can be led out of the crucible <NUM> and into the trap <NUM>. For instance, the gas introduced through the inlet <NUM>, and vaporized radioisotopes, are discharged from the outlet <NUM>. The radioisotopes are substances generated through irradiation of a liquid target with a radiation beam.

The trap <NUM> is a device for separating and extracting the radioisotope from the gas introduced from the crucible <NUM>. The trap <NUM> is hermetically connected to the crucible <NUM>, so as to enable conveyance of a gas containing the radioisotopes. For instance, the gas introduced from the crucible <NUM> is cooled in the trap <NUM>. As a result, it becomes possible to separate radioisotopes from the gas (typically a mixed gas with He) that contains the radioisotopes, through liquefaction or solidification of the radioisotopes. The cooling is not particularly limited as long as the radioisotopes can be separated from the gas mixture; for instance, the cooling temperature may be set to be equal to or lower than the boiling points of the radioisotopes, and preferably equal to or lower than the melting points or equal to or lower than the freezing points of the radioisotopes. More preferably, the cooling temperature is set to be lower than the melting points and the freezing points of the radioisotopes. For instance, the cooling temperature can be set to be <NUM> (<NUM>) or lower, typically - <NUM> (<NUM>) or lower, preferably -<NUM> (<NUM>) or lower, and more preferably -<NUM> (<NUM>) or lower. For instance, cooling water, acetone-dry ice, liquid nitrogen or the like can be used as a cooling means. The radioisotopes can be separated herein since He gas does not liquefy or solidify at the temperature of liquid nitrogen (<NUM>). The separated gas (for instance He gas), discharged from the trap <NUM>, may be introduced again through the inlet <NUM> into the crucible <NUM>. In the trap <NUM> the radioisotopes can be separated in accordance with a method similar to conventionally known dry distillation. The trap <NUM> is an example of an extraction unit.

A temperature measuring means such as one or more thermocouples may be disposed in the crucible <NUM>. The temperature measuring means allows measuring the temperature at a position of the liquid phase and the temperature at the position of the gas phase, in the crucible <NUM>. It is for instance possible to determine whether the target-constituting substance is liquefied or not, through measurement of the temperature of the liquid phase position.

<FIG> is a diagram illustrating an example of the operation flow of the radioisotope producing apparatus. Herein a target-constituting substance is already disposed in the crucible <NUM>. A predetermined amount of He gas per unit time is introduced through the inlet <NUM>.

In S101, the heater <NUM> of the radioisotope producing apparatus <NUM> heats up the crucible <NUM>. The heater <NUM> may be controlled for instance by a control device, for instance by a computer or the like. The target-constituting substance in the crucible <NUM> is heated (typically, melted to a liquid) as a result of heating of the crucible <NUM>. Preferably, the crucible <NUM> is heated to a temperature at or above the melting point of the target-constituting substance. The target-constituting substance having become a liquid will also be referred to as liquid target. Herein bismuth (Bi) serves as the target-constituting substance. The target-constituting substance is for instance an element of group <NUM>, group <NUM> or group <NUM> of the periodic table. The melting point of bismuth is <NUM>, and accordingly it suffices to heat up the crucible <NUM> at a temperature of <NUM> or higher. Herein the crucible <NUM> is set to be heated to <NUM> by the heater <NUM>. The temperature of the target (liquid target) is preferably a temperature at which the proportion of the saturated vapor pressure of the respective generated radioisotope, relative to the saturated vapor pressure of the liquid target, is high. In order to efficiently obtain an objective radioisotope, it is preferable to select a respective target element such that the proportion of the saturated vapor pressure of the generated radioisotope relative to the saturated vapor pressure of the liquid target is high. The type of the radiation beam to be projected in this case is selected as described further on.

In S102, the liquid target in the crucible <NUM> is irradiated with a radiation beam, via the beam port <NUM>. Examples of radiating of the radiation beam include for instance α-beams (<NUM>He<NUM>+), <NUM>He<NUM>+, <NUM>H+, <NUM>H+, <NUM>Li<NUM>+ and the like. Herein α-beams serve as the radiating of the radiation beam. The radiation beams utilized are <NUM>H+, <NUM>H+, <NUM>He<NUM>+, <NUM>He<NUM>+ or <NUM>Li<NUM>+ in a case where target-constituting substance is an element of group <NUM>, group <NUM>, group <NUM> or group <NUM>. In consequence, the main radioisotopes generated as a result of a nuclear reaction between the target-constituting substance and the radiation beam are elements of group <NUM>, group <NUM>, group <NUM> and group <NUM>. Preferably, the element of the target is a metal.

In S103, a radioisotope is generated as a result of a nuclear reaction between the target-constituting substance and the radiation beam. The target-constituting substance is Bi, and the main radioisotope that is generated is <NUM>At, when the radiation beam is α-beams. Within the liquid phase of the crucible <NUM>, moreover, Bi warmed by the heat of the nuclear reaction rises up, whereas Bi cooled by the gas in the gas phase, or air or the like passing through the wall of the crucible <NUM>, descends; convection of Bi is driven thereby. The temperature of Bi in the liquid phase can be kept constant thereby.

In S104, the radioisotope generated through irradiating with the radiation beam evaporates. For instance, the saturated vapor pressure of At, at the melting point (<NUM>), is <NUM>×<NUM><NUM> Pa. The generated At evaporates until the partial pressure of At in the crucible <NUM> reaches the saturated vapor pressure. For instance, the saturated vapor pressure of Bi at the melting point (<NUM>) is <NUM>×<NUM>-<NUM> Pa. The generated Bi evaporates until the partial pressure of Bi in the crucible <NUM> reaches the saturated vapor pressure. Assuming that the saturated vapor pressure of At, at the melting point of Bi (<NUM>), is substantially the same as the saturated vapor pressure at the melting point of At (<NUM>), then the saturated vapor pressure of At is <NUM><NUM> times or more larger than the saturated vapor pressure of Bi. In the liquid phase of the crucible <NUM>, therefore, most of the elements that evaporate from the liquid surface (elements migrating from the liquid phase to the gas phase) is At, since the partial pressure of Bi reaches immediately the saturated vapor pressure in the gas phase, even if the proportion of At with respect to Bi is very small. In a case for instance where the temperature of the liquid target is <NUM>, the proportion of At in the elements evaporated from the liquid surface is <NUM>% or higher, if the volume of Bi is appropriately set. That is, At constitutes most of the elements that evaporate from the liquid surface. The amount of At present in the gas phase is much larger than the amount of Bi present in the gas phase. Thus, At becomes separated from Bi as a result.

In a case where the saturated vapor pressure of an element generated by irradiation is high relative to the saturated vapor pressure of the target-constituting element, the greater part of the element evaporated from the liquid surface of the liquid phase is the element (radioisotope) to be generated. The radioisotope migrates into the generated gas phase (into the gas) as a result of irradiation of the target-constituting element with a radiation beam.

<FIG> is a table illustrating examples of the relationship between the saturated vapor pressure of elements in group <NUM>, group <NUM>, group <NUM> and group <NUM>, and temperature. For instance, the saturated vapor pressure of Ge in group <NUM>, at <NUM>, is <NUM><NUM> Pa. It is known that in principle the saturated vapor pressure of an element increases monotonically with temperature. The saturated vapor pressures of elements of a same period are compared herein. In the table of <FIG>, a comparison between identical saturated vapor pressures reveals that the temperatures in the elements of group <NUM>, group <NUM> and group <NUM> are higher than the temperatures in group <NUM>. In a comparison at a same temperature, the saturated vapor pressures of elements of group <NUM>, group <NUM> and group <NUM> are lower than the saturated vapor pressures of elements of group <NUM>. Generally, the boiling points of elements of group <NUM> are very much lower than the boiling points of other elements. In a comparison at a same temperature, therefore, the saturated vapor pressures of elements of group <NUM>, group <NUM> and group <NUM> are lower than the saturated vapor pressures of elements of group <NUM>. That is, the saturated vapor pressures of the elements of group <NUM>, group <NUM> and group <NUM>, at the melting points of the elements of group <NUM>, group <NUM> and group <NUM>, are lower than the saturated vapor pressures of the elements of group <NUM> and group <NUM> at the melting points of the elements of group <NUM>, group <NUM> and group <NUM>. In other words, the elements of group <NUM> and group <NUM> are gaseous at the melting points of the elements of group <NUM>, group <NUM> and group <NUM>. The proportion of radioisotope with respect to the element evaporated from the liquid surface rises through the use of an element of group <NUM>, group <NUM> or group <NUM> as the liquid target, and by setting an element of group <NUM> or group <NUM> as the element (radioisotope) to be generated.

In S105 the radioisotope (for instance <NUM>At) evaporated from the liquid surface of the liquid phase into the gas phase passes through the outlet <NUM> together with for instance He gas of the gas phase and reaches the trap <NUM>. The radioisotope is extracted in the trap <NUM> for instance through cooling using liquid nitrogen or the like. At the time of cooling with liquid nitrogen, He gas remains as a gas, and slips through the trap <NUM>, whereas the radioisotope remains in the trap <NUM>, for instance by solidifying. The radioisotope can be separated and extracted as a result.

In the radioisotope producing apparatus <NUM> the radioisotope can be separated and extracted in the trap <NUM> while the radiation beam goes on being projected. In the radioisotope producing apparatus <NUM>, specifically, radiating of the radiation beam and extraction of the radiation isotope can be performed in parallel. When radiating of the radiation beam and extraction of the radiation isotope are parallel, either one of the processes of radiating of the radiation beam and extraction of the radiation isotope may be discontinued. The target element need not be removed from the crucible <NUM> at the time of extraction of the radioisotope. As a result, the radioisotope producing apparatus <NUM> allows generating radioisotopes efficiently.

<FIG> is a diagram illustrating a configuration example of a radioisotope producing apparatus. A radioisotope producing apparatus <NUM> in <FIG> has a crucible <NUM>, a heater <NUM>, a nozzle <NUM>, a beam port <NUM>, a beam window <NUM>, a beam window <NUM>, an inlet <NUM>, an outlet <NUM>, a trap <NUM>, a pump <NUM> and a heat exchanger <NUM>. The radioisotope producing apparatus <NUM> may have a jacket for cooling of the crucible <NUM>, similarly to the radioisotope producing apparatus <NUM> in <FIG>.

The crucible <NUM>, the heater <NUM>, the beam port <NUM>, the beam window <NUM>, the beam window <NUM>, the inlet <NUM>, the outlet <NUM> and the trap <NUM> have configurations identical to those of corresponding members of the radioisotope producing apparatus <NUM>.

A passage for discharging a liquid target is provided at the bottom of the liquid phase of the crucible <NUM>, such that a liquid target is discharged from the crucible <NUM> by the action of the pump <NUM>. The discharged liquid target is cooled by the heat exchanger <NUM>. The cooled liquid target is introduced into the nozzle <NUM> disposed at the top in the crucible <NUM>. The liquid target introduced into the nozzle <NUM> flows in waterfall fashion from the bottom of the nozzle <NUM> and reaches the liquid phase of the crucible <NUM>. The beam port <NUM> is installed so that the liquid target flowing out of the nozzle <NUM> is irradiated with a radiation beam. Heat generated by nuclear reactions can be efficiently removed and rises in the temperature in the crucible <NUM> can be suppressed, through forced circulation of the liquid target.

The radioisotope producing apparatus <NUM> operates in the same manner as the radioisotope producing apparatus <NUM>, except for the portion in which the liquid target is forcibly caused to circulate.

Solid targets attached to an apparatus have conventionally been irradiated with a radiation beam, to generate a radioisotope within the solid target. In consequence, the solid target attached to the apparatus was removed after irradiation, and the radioisotope was extracted through dry distillation of the solid target, for instance by heating and dissolution. A time loss was thus incurred in the process from removal of the solid target until dry distillation was complete. Further, irradiation of a solid target necessitated herein curtailment of the irradiation output, so as to preclude melting of the solid target. Curtailing thus the output entails a reduction in the amount of generated radioisotope.

In the apparatus of the present second embodiment, by contrast, a liquid target is irradiated with a radiation beam, to generate a radioisotope within the liquid target. The proportion of the generated radioisotope that evaporates, relative to the element that evaporates from the liquid phase, can be increased through proper adjustment of temperature and pressure in the vicinity of the liquid surface of the liquid target. In the above example, the saturated vapor pressure of <NUM>At is much higher than the saturated vapor pressure of Bi, and hence <NUM>At makes up most of the elements that evaporate from the liquid phase. Accordingly, the radioisotope is purified through recovery of the evaporated element. The process of generation, separation, and purification of the radioisotope proceeds spontaneously until the partial pressure of <NUM>At in the vicinity of the liquid surface of the liquid target reaches a saturated vapor pressure and an equilibrium state is attained. Therefore, <NUM>At can go on being produced, continuously or intermittently, if At is extracted continuously or at appropriate timings. In the apparatus of the present second embodiment the radioisotope can be extracted without discontinuation of irradiating of the liquid target with the radiation beam, and without removal of the liquid target, and hence producing of the radioisotope, from generation up to extraction, can be accomplished in a shorter time. That is, the apparatus of the present second embodiment allows extracting a radiation isotope from a gas that contains an evaporated radiation isotope generated through irradiation with a radiation beam.

In the apparatus of the present second embodiment the target is a liquid, and accordingly it is not necessary to suppress the output of irradiation so as to preclude melting of the target, and the irradiation output of the radiation beam can be kept large, without rises in the temperature of the liquid target, through cooling of the liquid target for instance by convection or forced circulation. A greater amount of radioisotope can be produced by increasing the irradiation output.

Examples have been explained, in the above embodiments and variations, of an instance where bismuth (Bi) is used as the target substance and α-beams are used as the radiation beam that irradiates the target substance, to thereby generate <NUM>At as a radioisotope. In the above embodiments and variations, however, a metal other than bismuth (Bi) may be used as the target substance, a radiation beam other than α-beams may be used to irradiate the target substance, and a radioisotope other than <NUM>At may be generated.

The tables below set out combination patterns of target substances, radiation beams and radioisotopes that can be used in the above embodiments and variations.

The description in the column notated as "Target" in the above tables exemplifies elements that can be used as a target substance in the above embodiments and variations; as set out in the tables, the elements may be for instance sulfur (S), gallium (Ga), selenium (Se), tin (Sn), antimony (Sb), tellurium (Te), lead (Pb) and bismuth (Bi).

The description in the column notated as "nuclear reaction" in the above tables exemplifies the types of nuclear reaction elicited by the radiation beam that irradiates the target substance, in the above embodiments and variations; as set out in the tables, the nuclear reaction may be for instance an α-reaction using α-particles, a p reaction using protons, and a nuclear reaction using lithium. In the column of nuclear reaction, the descriptor to the left of the comma represents the particle that strikes the target substance, and the descriptor to the right of the comma represents the particle emitted by the target substance.

The description in the column "Progeny nuclide" in the tables denotes the nuclide that is generated through product decay. As set out in the tables, examples of progeny nuclides include germanium (Ge) and bromine (Br). Instances where a variety of progeny nuclides are generated that do not fit into the column of the tables are marked with an asterisk (*).

The descriptions in the column "Target" and column "Product" of the column notated as "Heating temperature" denote the state of the respective substance. The caption "Sol" denotes a solid state, "Liq" denotes a liquid state, and "Gas" denotes a gaseous state.

Various radioisotopes can be generated in the above embodiments and variations, as set out in the column "Product" of the tables, by utilizing the combinations of target and nuclear reaction given in the tables. In the above tables, the target denotes a substance the temperature of which, at the time of vaporization at the pressure upon irradiation with the radiation beam, is higher than the temperature at which the radioisotope, as the product, vaporizes under that same pressure. In the above embodiments and variations, therefore, a radioisotope can vaporize, without vaporization of the target substance, and can be extracted from the gas in the trap <NUM>, by adjusting the temperature of the target substance so as to lie in a temperature range that is equal to or higher than the temperature at the time of vaporization of the radioisotope, under a same pressure, and that is lower than the temperature at the time of vaporization of the target substance under that same pressure. The term "vaporization" in the present application signifies that a substance that has reached a gaseous state and encompasses conceptually for instance a state resulting from transition to a gas phase by going beyond the boiling point or the sublimation point of that substance. Accordingly, the wording "temperature at the time of vaporization of a target substance, under a same pressure" can be rephrased as "boiling point or sublimation point at which a target substance evaporates, under a same pressure".

For instance in the combination No. <NUM> in the tables, the boiling point at normal pressure of sulfur (S) which is the target substance is about <NUM>, whereas the boiling point at normal pressure of chlorine (Cl) which is the product is about -<NUM>, lower than that of sulfur (S). Accordingly, if the target is irradiated with a radiation beam in a state where the temperature in the crucible <NUM> is <NUM>, as indicated in the column "Heating temperature" of the tables, then sulfur (S) which is the target substance remains in a liquid state, while only chlorine (Cl) which is the product evaporates in the crucible <NUM>, the chlorine (Cl) having evaporated in the crucible <NUM> being then condensed in the trap <NUM>, to be extracted as a result.

For instance in the combinations No. <NUM> and No. <NUM> in the tables, the boiling point at normal pressure of gallium (Ga) which is the target substance is about <NUM>, whereas the boiling point at normal pressure of arsenic (As) which is the product is about <NUM>, lower than that of gallium (Ga). Accordingly, if the target is irradiated with a radiation beam in a state where the temperature in the crucible <NUM> is <NUM>, as indicated in the column "Heating temperature" of the tables, then gallium (Ga) which is the target substance remains in a liquid state, while only arsenic (As) which is the product evaporates in the crucible <NUM>, the arsenic (As) having evaporated in the crucible <NUM> being then condensed in the trap <NUM>, to be extracted as a result.

For instance in the combinations No. <NUM>, No. <NUM> and No. <NUM> in the tables, the boiling point at normal pressure of selenium (Se) which is the target substance is about <NUM>, whereas the boiling point at normal pressure of bromine (Br) which is the product is about <NUM>, lower than that of selenium (Se). Accordingly if the target is irradiated with a radiation beam in a state where the temperature in the crucible <NUM> is <NUM> or <NUM>, as indicated in the column "Heating temperature" of the tables, then selenium (Se) which is the target substance remains in a liquid state, while only bromine (Br) which is the product evaporates in the crucible <NUM>, the bromine (Br) having evaporated in the crucible <NUM> being then condensed in the trap <NUM>, to be extracted as a result.

For instance in the combinations No. <NUM> and No. <NUM> in the tables, the boiling point at normal pressure of antimony (Sb) which is the target substance is about <NUM>, whereas the boiling point at normal pressure of iodine (I) which is the product is about <NUM>, lower than that of antimony (Sb). Accordingly, if the target is irradiated with a radiation beam is in a state where the temperature in the crucible <NUM> is <NUM> or <NUM>, as indicated in the column "Heating temperature" of the tables, then antimony (Sb) which is the target substance remains in a solid or liquid state, while only iodine (I) which is the product evaporates in the crucible <NUM>, the iodine (I) having evaporated in the crucible <NUM> being then condensed in the trap <NUM>, to be extracted as a result.

For instance in the combination No. <NUM> in the tables, the boiling point at normal pressure of bismuth (Bi) which is the target substance is about <NUM>, whereas the boiling point at normal pressure of radon (Rn) which is the product is about -<NUM>, lower than that of bismuth (Bi). Accordingly if the target is irradiated with a radiation beam in a state where the temperature in the crucible <NUM> is <NUM> or <NUM>, as indicated in the column "Heating temperature" of the tables, then bismuth (Bi) which is the target substance remains in a solid or liquid state, while only radon (Rn) which is the product evaporates in the crucible <NUM>, the radon (Rn) having evaporated in the crucible <NUM> being then condensed in the trap <NUM>, to be extracted as a result.

In the column "Heating temperature" of the tables, two instances, of temperature of <NUM> and <NUM> are illustrated. However, the temperature in the crucible <NUM>, when a combination of target and nuclear reaction set out in the above tables is to be implemented in the above embodiments and variations, is not limited to either <NUM> or <NUM>. The temperature of the target substance in the crucible <NUM>, in a case where a combination of target and nuclear reaction set out in the tables above and to be implemented in the above embodiments and variations, is set to an arbitrary temperature within a temperature range that is equal to or higher than the temperature at the time of vaporization of the product under the pressure in the crucible <NUM> and that is lower than the temperature at the time of vaporization of the target substance under that same pressure. For instance in the combination No. <NUM> in the tables, the boiling point at normal pressure of sulfur (S) which is the target substance is about <NUM>, whereas the boiling point at normal pressure of chlorine (Cl) which is the product is about -<NUM>, lower than that of sulfur (S). Accordingly, assuming that the interior of the crucible <NUM> is at normal pressure, if the temperature of sulfur (S) in the crucible <NUM> lies in the range from about -<NUM> to about <NUM> then just chlorine (Cl), which is the product, can be allowed to evaporate in the crucible <NUM>, without vaporization of sulfur (S) which is the target substance, whereupon the chlorine (Cl) having evaporated in the crucible <NUM> can be extracted by being condensed in the trap <NUM>.

The column "Target" in the above tables sets out only the name of the target-constituting element, but two or more types of target substance may be held in the crucible <NUM>, or a substance other than a target may be present, along with the target substance, in the crucible <NUM>, provided that a substance serving as a target, such as those in the column "Target" of the tables, is contained in the crucible <NUM>.

In a case where an alloy is formed in the crucible <NUM> by charging two or more types of substance together, the melting point is different from that in a case where respective substance is present alone in the crucible <NUM>. For instance, the melting point of an alloy produced at a <NUM>:<NUM> ratio of bismuth (Bi) and tin (Sn), at normal pressure, is <NUM> i.e. lower than <NUM>, which is the melting point of bismuth (Bi), and lower than <NUM>, which is the melting point of tin (Sn). However, the boiling point itself of a product obtained by irradiating bismuth (Bi) with a radiation beam and the boiling point itself of a product obtained by irradiating tin (Sn) with a radiation beam are unrelated, regardless of whether the foregoing are in an alloyed state or not, and accordingly the products can be extracted selectively in the trap <NUM>, through adjustment of the interior of the crucible <NUM> to an appropriate temperature.

Claim 1:
A method for producing a radiolabeled compound, comprising the steps of:
irradiating an alloy as a target substance with a radiation beam, to generate two or more radioisotopes from the alloy, and allowing the two or more radioisotopes to migrate into a gas; and
generating an intermediate label by allowing a first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with a label precursor; characterized in that the method further comprises:
generating a final label by allowing a second radioisotope different from the first radioisotope, from among the two or more radioisotopes having migrated into the gas, to react with the intermediate label.