Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Reexamination Certificate
2001-07-18
2004-08-10
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
C423S249000, C423S500000, C423S503000
Reexamination Certificate
active
06773686
ABSTRACT:
The invention relates to a process for the purification and/or concentration of (radio)isotopes, a process for the purification of iodine isotopes, a process for obtaining a transportable form of isotopes and an apparatus therefore and a transportable form of isotopes.
Radiopharmaceuticals are used for diagnostic and therapeutic application in Nuclear Medicine. During the last decade, internal radiotherapy has become increasingly popular, particularly in the fields of oncology, endocrinology and rheumatology. Isotopes with a long half-life (>4 days) e.g. iodine-131 and strontium-89, have been in use for this kind of therapy. It is important that these isotopes emit &agr;- and/or &bgr;-particles in order to achieve the desired absorbed radiation dose in target tissue (e.g. tumour tissue).
Diagnostic isotopes in general have a short half-life(<4 days) with a &ggr;-decay (e.g. technetium-99 and iodine-123), and are used for localisation and visualisation of tumours, inflammation or metabolic diseases.
Radiopharmaceuticals are compounds that play an active role in the determination of biological processes by coupling to peptides or proteins. These compounds are labelled with an appropriate radio-isotope. The biologically active part is often responsible for seeking the target tissue. Diagnostic &ggr;-emitting isotopes can be detected with a &ggr;-camera to visualise the target tissue (e.g. tumour). The radiation dose for the patient will be kept as low as reasonable (ALARA=As Low As Reasonably Achievable principle). For therapeutical use, a high and selective uptake and long retention of the isotopes in the target is important in order to destroy the diseased tissue.
There is a large number of iodine isotopes which are used in nuclear medicine, especially for thyroid studies, where the (radio) iodine reacts with the tyrosine. Table 1 shows an overview of the most frequently used radio-iodinated compounds.
TABLE 1
Frequently used radio-iodinated compounds.
isotope
labelled molecule
target organ
Iodine-123/131
Hippuran
kidney
Iodine-123
Iomazenyl
brain
Iodine-123/131
Sodium iodide
thyroid
Iodine-123
MIBG
adrenals (marrow)
Iodine-131
Norcholesterol
adrenals (cortex)
Radioiodine is an important radioisotope in nuclear medicine, for various applications (SPET, PET, and radioimmunotherapy). This wide-spread use in nuclear medicine implies meeting specifications, such as radionuclidic purity (e.g. low level of
121
Te which is a by-product in the production of
123
I) and radiochemical purity (e.g. absence of radioiodine containing impurities such as iodate or periodate compounds but also in the absence of
121
Te, which is a by-product in the production of
123
I).
Fulfilment of these requirements are a ‘conditio sine qua non’ for an efficient production (high labelling yield) of radioiodinated pharmaceuticals. In earlier developed methods such as anion-exchange chromatography (Good et al., 1958, Harper et al., 1963) traces of (oxygenated) radioiodine containing impurities were not completely removed due to insufficient selectivity. The use of a distillation-process whether wet (Acerbi et al., 1975) or dry (Weinreich et al., 1996), is not only less practical, but in the case of no-carrier-added radioiodide, may also lead to hazardous and unwanted generation of impurities due to heating. Sometimes in these processes, presence of radioiodide impurities can be suppressed by addition of traces of reducing agents.
A concentration-purification process based on the adsorption/desorption features of radioiodide for platinum (Case et al., 1966, Kondo et al., 1977) has been described previously. In this method, radioiodide from an acidified solution was adsorbed, on a platinum surface (e.g. foil or felt), that was pre-treated with hydrogen-gas, and desorbed electrochemically (Toth, 1961), or by heating in a sulphite-containing alkaline-solution (Kondo et al., 1977). Adsorption and desorption were not quantitative (ca 80% and 60%, respectively), while the whole process is laborious and time consuming.
It is a goal of the present invention to provide a swift and reliable method for the purification of radioiodine. This method must be able to fulfil the high requirements for radiochemical purity as well as radionuclidic purity. The method should have a large capacity, contain little or no contamination with tellurium compounds, have a stable and reproducible yield and provide the radioisotope in the iodide form.
The method should also be capable of providing the radioiodide in a concentrated form, thus providing for a more efficient handling. Hence it is another goal of the invention to provide a method for the concentration of radioiodine.
It is also another goal of the present invention to provide for a method which is suitable as production-method, and is able to provide reductive properties for removing radiochemical impurities of the radioiodide, thereby obtaining a high recovery (>95%).
Accordingly, the invention comprises a process for the purification of radioisotopes wherein the isotopes are dissolved in a dilute acidic solution and adsorbed on a surface (optionally activated) of a d
10
-metal whereby the isotopes are selectively desorbed by elusion with an eluent in the presence of hydrogen.
It is possible that the terms iodide and iodine may be used in an interchangeable manner. This may be attributed to the mechanism of the adsorption-desorption process which is not fully elucidated. This does not detract from the concept and scope of the present invention.
Alterations on adsorption-material, as well as elution-conditions result in different embodiments of the invention and in an efficient process in which radiochemical pure radioiodide is obtained in a reproducible yield (>95%) with a high-recovery. A high yielding procedure comprising steps of the invention is one wherein a column is filled with the iodine absorbing metal such as platinum. The metal is optionally activated by purging with hydrogen gas. Subsequently an acidic solution containing the radioiodine is brought on the column and the radioiodine is absorbed on the metal. When platinum is used, the column has also reductive properties, thus reducing possible oxidation products of iodide such as iodate or periodate to iodine. After the iodide is absorbed, the column is rinsed to remove other impurities present in the load solution in such way that the iodide remains absorbed on the metal. Subsequently, the iodide is eluted in the form of iodine with a basic solution, optionally containing other components such as hydrogen. The purified iodine is collected and ready for further use.
By eluting the column with a suitable eluent the iodine is obtained in a concentrated form. One aspect of the invention therefore is a process for the concentration of radioisotopes wherein the isotopes are dissolved in a dilute acidic solution and adsorbed on the surface (optionally activated) of a d
10
-metal whereby the isotopes are selectively desorbed by elution with an eluent in the presence of hydrogen.
Another aspect of the invention relates to the combined concentration and purification of radioisotopes. Accordingly, the invention relates to a process for the purification and concentration of radioisotopes wherein the isotopes are dissolved in a dilute acidic solution and adsorbed on the surface (optionally activated) of a d
10
-metal whereby the isotopes are selectively desorbed by elution with an eluent in the presence of hydrogen.
In an preferred embodiment of the invention, the d
10
-metal is platinum.
In a preferred embodiment of the invention the metal is positioned in a column, whereby the column is filled with the iodine adsorbing metal. Any column, known in the art will suffice, such as a chromatography column, which can be a simple glass, metal or plastic column or tube of any size and diameter.
The metal can be in any suitable form, with or without a carrier material such as carbon, silica, alumina or other carrier materials which are itself known in the art. The form of the metal is not crucial, as long as the
Herscheid Jacobus D. M.
Moet Frits Peter
Bos Steven
Mallinckrodt Inc.
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