Method to produce radionuclide bismuth-212

FIELD: power engineering.

SUBSTANCE: method to produce a radionuclide bismuth-212 from a nitrate solution containing a mixture of radionuclides thorium-228, thorium-229 and their daughter products of decay, and release of the finished product at an ion-exchange column with cationite. The nitrate solution contains a mixture of radionuclides thorium-228 and thorium-229 and their daughter products of decay, is mixed with ethyl alcohol, this mixture is eluted via the ion exchange column with cationite, where all cations contained in the mixture are absorbed, and as bismuth-212 is accumulated, bismuth-212 is washed by diluted hydrochloric acid.

EFFECT: simplified technological process of production of a radionuclide bismuth-212.

3 cl

 

The technical FIELD

The invention relates to a technology for production of radionuclides for nuclear medicine, in particular for the treatment of cancer.

In the treatment of cancer becoming more widely used are α-emitting radionuclides. This is due to the large initial energy (5-8 MeV) and short run (tens of microns) of α-particles in biological tissues and, consequently, a high level of energy in the field of localization decaying nuclides. The native α-emitting radionuclides (monoclonal antibodies, peptides and other) with high specificity can deliver them right into the tumor site or metastatic lesion. Due to the small runs of α-particles is possible selective effects of radiation on pathological objects with minimal radiation exposure to surrounding healthy tissues.

The present invention can be used to create generators α-emitters thorium-228/bismuth-212 (228Th/212Bi), thorium-228/lead-212 (228Th/212Pb) and thorium-229/bismuth-213 (229Th/213Bi), finite elements in the decay chain which radionuclides lead-212, bismuth-212 and bismuth-213 - can be used as part of medical radiopharmaceuticals.

PRIOR art

One of the most promising directions in nuclear medicine is one who by radioimmunotherapy using α-emitters. The use of short-lived α-emitting radionuclides for cancer therapy is of interest from a radiobiological point of view, because it is the most effective way of lethal destruction of tumor cells due to the high ionizing ability of α-particles in tissue.

Currently, a search for α-emitters with acceptable nuclear-physical properties. Radionuclide bismuth-212, formed by the decay of the isotope uranium-232 is one of the most promising for use in cancer treatment.

The half-life of bismuth-212 is 60.6 min, the average energy of the α particles of 7.8 MeV. In the decay of bismuth-212 sequentially formed radionuclide polonium-212 thallium-208 and stable nuclide Pb-208. Mileage α-particles in biological tissue is less than 100 μm, which corresponds to just a few diameters of a cancer cell, and linear energy transfer (let) reaches ~80 Kev/µm. Diagram of the formation of bismuth-212 shown below.

The initial element of a chain of uranium-232 is an artificial isotope of uranium, the formation of which occurs in a nuclear reactor by irradiation of natural thorium in the following reactions interaction of neutrons and gamma-quanta with the nuclide thorium-232:

232Th(n,γ)233Th→233Pa(γn) 232Pa→232U

232Th(n,2n)231Th→231Pa(n,γ)232Pa→232U

232Th(γ,n)231Th→231Pa(n,γ)232Pa→232U.

Depending on the conditions of irradiation of thorium in a reactor equilibrium concentration of uranium-232 is in the range 1000-6000 mm. ppm [Wemmerlov, Mofchanov, Angeles. "The use of thorium in nuclear reactors". Energoatomizdat. M., 1983].

During irradiation of thorium in a reactor simultaneously with uranium-232 is the formation of uranium-233 by the following reaction:

232Th(n,γ)→233Th→233Pa→233U.

In the α-decay of uranium-233 is formed thorium-229, which in turn after a number of disintegrations enters the radionuclide bismuth-213.

Radionuclide bismuth-213 has the advantage, based on a significantly lower dose of the concomitant γ-radiation compared with bismuth-212. However, bismuth-212 is produced much faster due to the relatively short half-life of its predecessor - thorium-228. The ratio of the half-life of thorium-229 and thorium-228 is ≈3800. In the early stages of biomedical research (the study of stability of bioconstruction, their tagging alpha-emitting product), preclinical testing of drugs and other preliminary experiments can be used bismuth-212.

In terms of long-term future is willow production of α-emitters in nuclear medicine key important radionuclides thorium-228 and thorium-229. Proposed several ways to obtain these radionuclides [Isotopes: properties, production, application. In 2 volumes. Tom. Edited Vounaria. M, FIZMATLIT, 2005, str-389]:

- from stocks isotope uranium233U;

in a nuclear reactor as a result of multiple captures of neutrons isotope of radium226Ra the reaction226Ra(3n,2β)229Th;

in a nuclear reactor during irradiation isotope of thorium230Th fast neutrons in the reaction230Th(n,2n)229Th;

as a result of exposure230Th protons at the cyclotron reactions230Th(p,pn)229Th and230Th(p,2n)229Pa(1,4 d, β-)229Th.

In all of these ways the irradiation of natural thorium at the same time with thorium-229 is accumulated and radionuclide thorium-228. For example, during irradiation in the reactor radium-226 share of thorium-228 in the target reaches huge values - depending on the irradiation conditions from 25 to 50 wt.% [Wounaan, Nsamankow. Nuclide programs RRC "Kurchatov Institute": past, present, future // Conversion in mechanical engineering. No. 3, 2000, p.38-47].

Currently available source of raw materials for the production of bismuth-213 and bismuth-212 are old stocks of uranium-233 containing an admixture of uranium-232. Given the large difference in half-life of thorium-229 and thorium-228, from this material, depending on the lifespan and its extracts can be obtained practically pure thorium-228 (extract 0.5-1 year) or after a longer exposure to get a mixture of thorium-228 and thorium-229, in which after soaking in 15-20 years will remain only thorium-229.

Bismuth-212 is a typical radionuclide generator and finds use in radioimmunotherapy, mainly in the form of labelled them of monoclonal antibodies and other molecular carriers. Today for bismuth-212 use two generator system228Th/224Ra and224Ra/212Bi. In the first of these radium-224 is separated from the thorium-228 due to the anion-exchange separation of these radionuclides from solution of nitric acid. In the second generator with the use of cation exchange resins and mineral acids from radium-224 allocate bismuth-212 [R.W.Atcher, A.M.Friedman, J.J.Hines "An improved generator for the production of212Pb and212Bi from224Ra". International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, Volume 39, Issue 4, 1988, Pages 283-286].

A prototype of the selected method of producing bismuth-212, described in [Vmoshninov, Webpublic, ASI and other "Control of technological processes in the development of medical generators225Ac/213Bi and224Ra/212Bi alpha - and gamma-spectrometric methods" // Nuclear energy, No. 3, 2003, str-126].

As a source of raw material for radionuclide bismuth-212, the authors used a solution containing a mixture of radionuclides thorium-228, thorium-229 and their daughter products decay. To obtain a bismuth-12 performed the following procedures:

- radionuclide thorium-229, th-228, and the resulting daughter decay products of these radionuclides were sustained (not less than 14 days) in the solution of nitric acid for the accumulation of the radionuclide radium-224;

- after soaking solution (8M HNO3)containing radionuclides of the thorium-229, thorium-228 and radium-224 and other daughter decay products was passed through a column of anion exchange resin;

- radionuclide thorium-229 and thorium-228 remained in the column with anion exchange resin, and radium-224 and other daughter decay products of thorium-229 and thorium-228 were collected at the outlet of the column. For complete leaching of radium-224 and other daughter products of the decay of thorium-229 and thorium-228 with the column it was washed with small amount of nitric acid solution (8M HNO3);

- obtained solution containing radium-224 and other child products of the decay of radionuclides thorium-229 and thorium-228, was evaporated to dryness;

- the dry residue containing the radionuclide radium-224, was dissolved in hydrochloric acid;

- means of hydrochloric acid solution of radium-224 was passed through a column of cation exchange resin;

- radionuclide radium-224 remained in the column of cation exchange resin;

- the column containing the radionuclide radium-224, washed with hydrochloric acid;

- at the exit from the column with cation exchange resin was collected solution with radionuclide bismuth-212.

However, this method of producing bismuth-212 has a major drawback:

- nohost deny the process of obtaining bismuth-212 from a mixture of radionuclides thorium-228 and thorium-229 is laborious and time consuming compared to the half-life of bismuth-212, is carried out by sequential radiochemical selection of the radionuclide radium-224 by adsorption from the original solution of thorium-228 and thorium-229 and the next phase of the selection from a solution of radium-224 radionuclide bismuth-212.

DISCLOSURE of INVENTIONS

The objective of the invention is to simplify the technological process of production of the radionuclide bismuth-212.

This method for obtaining a radionuclide, bismuth-212 from nitric acid solution containing a mixture of radionuclides thorium-228, thorium-229 and their daughter products decay, and the selection of the final product on the ion exchange column with cation exchange resin, while the nitric acid solution containing a mixture of radionuclides thorium-228 and thorium-229 and their daughter products decay, mixed with ethyl alcohol, elute the mixture through an ion exchange column with cation exchange resin, which absorb all contained in a mixture of cations and the accumulation of bismuth-212 wash bismuth-212 diluted hydrochloric acid. The content of ethyl alcohol in the nitric acid solution is 70-95%. In addition, the concentration of hydrochloric acid is 0.1-0.5 M

Known for the ability to change the value of the coefficient distribution in ion exchange processes using acid solutions mixed with rectified methyl or ethyl alcohol (Guseva LI, Tikhomirova G.S., Dogadkin R.N. The Department is giving radium from alkaline-earth and actin-iodine elements on the anion exchange resin and water-methanol solutions of HNO 3. Generator227Ac-223Ra // radiochemistry, 2004, vol.46, No.1, p.54-58). This can be implemented as anion exchangers and cation exchangers. There are some regularities of changes in distribution coefficients when the elution solutions containing alcohol:

the distribution coefficients increased with increasing proportion of alcohol in the solution;

- a noticeable increase (1-3) distribution coefficients begins with approximately 70% of the alcohol content in the solution;

- on growth rate distribution ratio depending on the increase in alcohol concentration in the solution involved the elements can be arranged in a number of Th, Ra, Ac, Pb, Bi (Th - high speed growth, Bi - slow growth);

the concentration of the used acid in alcohol solution has little effect on the change of the coefficient of distribution of all involved elements, in addition to thorium.

Based on these patterns, you have defined the following process parameters:

- source solution for elution contains 70-95% ethyl alcohol (96.8 per cent) and 30-5% solution of radionuclides in 8M nitric acid;

- leaching of bismuth-212 spend diluted hydrochloric acid (0.1-0.5m HCl);

- with increasing concentration of the acid can be sequentially washed with Pb, Ac, Ra, Th.

The proposed method for radionuclide bismuth-212 has advantages which are relevant in comparison with the described prototype:

- eliminates sequential radiochemical redistribution solution containing a mixture of radionuclides thorium-228 and thorium-229 and daughter products of the decay of these radionuclides, simplifying the process of obtaining bismuth-212.

An EXAMPLE of carrying out the INVENTION

As a source of raw material for radionuclide bismuth-212 was used a solution of nitric acid containing a mixture of radionuclides thorium-228, thorium-229 and their daughter products decay. The solution was brought to a volume of 10 ml in 8M HNO3. Then the solution was brought to volume of 100 ml 96,8% ethyl alcohol. Derived nitric acid alcohol solution was blueraven through a column of cation exchange resin Dowex 50×4. The size of the column of 0.6×10 cm, the volume of 3.3 cm3. After elution the column was washed with 20 ml of a mixture of nitric acid (8M HNO3) and ethanol (ratio 1:10). The thus prepared ion-exchange column is used when a specific elution of the generator radionuclides bismuth or lead.

To obtain a bismuth-212 a mixture of radionuclides of the thorium-229, thorium-228 and their daughter products of the decay column was washed with diluted hydrochloric acid (0.3 m HCl). Through the column portions 5-10 ml was omitted ≈100 ml of diluted hydrochloric acid (0,3M HCl), which amounted to about 32 column volume. In 15 samples was not the traces of thorium, radium and sea anemone. Samples contained radionuclides bismuth and traces of lead-212 at the level of 0.2-0.05% in different samples. In the conducted experiment in the eluate was a mixture of radionuclides bismuth (bismuth-212 and bismuth-213), and bismuth-212 was about 95-85% of the activity of the sample. The presence in the eluate bismuth-213 is connected with use as feedstock in the experiment a mixture of thorium-228 and thorium-229 in the ratio of 12:1.

When the concentration of hydrochloric acid up to 0,5M HCl composition of the eluate does not differ from the one described above (0,3M HCl, and then with increasing concentrations of hydrochloric acid begins to leach lead-212, but up to 2M HCl in the solution is registered only bismuth and lead.

The proposed method of producing bismuth-212 allows, in comparison with the method chosen for the prototype, significantly reducing the complexity of the process.

1. A method of producing a radionuclide bismuth-212 from nitric acid solution containing a mixture of radionuclides thorium-228, thorium-229 and their daughter products decay, and the selection of the final product on the ion exchange column with cation exchange resin, characterized in that the nitric acid solution containing a mixture of radionuclides thorium-228 and thorium-229 and their daughter products decay, mixed with ethyl alcohol, elute the mixture through an ion exchange column with cation exchange resin, which absorb all contained in a mixture of Katie the s and the accumulation of bismuth-212 wash bismuth-212 diluted hydrochloric the acid.

2. The method according to claim 1, characterized in that the content of ethyl alcohol in the nitric acid solution is 70-95%.

3. The method according to claim 1, characterized in that the concentration of hydrochloric acid is 0.1-0.5 M



 

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