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<<   作成日時 : 2010/02/22 20:19   >>

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 診断検査に使用される重要なアイソトープ同位元素の不足の危機に対して、米国の会社がポーランド核エネルギー局との合意に達したという。年間100万人の検査に対応できるモリブデン99を提供できるという。
 モリブデン99は医療検査に使われるテクネシウム99mに移行する短寿命放射性同位体である。
 米国では毎日55,000人がテクネシウム99mを使った検査を受けている。アイソトープは基本的に5つの反応炉で生成されているが全てが45年以上たっており、米国には一つもない。カナダの反応炉はトリチウム漏れなどの問題で昨年5月以来閉鎖されており4月まで再開されない。オランダの反応炉は定期保守のため4〜6ヶ月閉鎖される。この2つの反応炉は米国で使用されるテクネシウム99mの約2/3を製造している。新しいオーストラリア反応炉は昨年製造し始めたばかりで制限がある。アイソトープは急速に減衰するため備蓄ができない。
 商業用の原子炉は同位元素を生成するためには使われていないので、オバマ政権はモリブデン99を作る新たな方法の開発に研究費を投入した。GE日立やミズーリ大で生成法を研究しているが、いつ可能となるかの見通しは立っていない。
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St. Louis company strikes deal with Poland for isotope that is crucial to medical tests
Covidien's agreement with Poland's Institute of Atomic Energy will allow radiologists to continue performing some tests. One official says it is only a short-term fix.
By Thomas H. Maugh II
February 17, 2010 | 11:04 a.m.
http://www.latimes.com/news/nation-and-world/la-sci-isotope18-2010feb18,0,5164808.story

As U.S. physicians face an impending crisis caused by lack of a crucial isotope used in many diagnostic procedures, a U.S. company said Wednesday that it had reached an agreement with the Polish nuclear energy agency to obtain the isotope from a reactor in that country.

Covidien, a St. Louis company that processes a radioisotope produced by reactors into a form that can be used in the medical tests, said that Poland's Institute of Atomic Energy will provide enough molybdenum-99 from the agency's Maria Research Reactor to meet the needs of about 1 million patients annually.

That is not nearly enough of the isotope to replace the shortage resulting from the shutdown of the two primary reactors that produce the element, but experts said it is enough to allow radiologists to keep performing some tests rather than shutting down.

"This is only a short-term fix to a long-term problem," said Robert W. Atcher, who heads a task force of SNM, formerly the Society of Nuclear Medicine, looking at ways to alleviate the shortage. The primary benefit of the new reactor may be for patients in Europe, he added in a statement.

Molybdenum-99 is a short-lived radioisotope that breaks down into technetium-99m (the m stands for metastable) -- the form that is used in medical tests. With a half-life of only six hours, the isotope allows physicians to examine blood flow and bones and identify tumors before quickly disappearing from the body, thereby minimizing radiation dose.

When supplies of technetium-99m are adequate, about 55,000 Americans every day and tens of thousands in the rest of the world undergo such tests. But the isotope is produced primarily in five reactors around the world, all of them over the age of 45 and none in the United States.

Canada's National Research Universal reactor in Chalk River has been shut down since last May because of tritium leaks and other problems and is not expected to reopen before April. A second major reactor, in Petten, the Netherlands, will close Friday for four to six months of scheduled maintenance. The two reactors account for about two-thirds of the technetium-99m used in the United States.

A newer Australian reactor began producing some molybdenum-99 last year, but only in limited quantities.

Because the radioisotope decays so fast, it cannot be stockpiled. As a consequence, technicians are scheduling tests at all hours of the day and night whenever they receive a supply. Many are also resorting to older, less efficient tests that have seen only limited use in the last 20 years.

Covidien said a test run was conducted last week at the Maria reactor -- named after Polish nuclear physicist Maria Skladowsky, best known as Marie Curie -- and the product is now being processed into technetium-99m at one of Covidien's European facilities. The company said it should begin distributing technetium-99m to European customers within 30 days.

But some complications remain. The company has to get permits from five countries to ship the molybdenum through them to its processing facility. The U.S. Food and Drug Administration must also test the finished product before it can be used in this country.

Meanwhile, the Obama administration has been funneling some stimulus funds into developing new ways to produce molybdenum-99.

The current procedure involves inserting a high-grade uranium target into a reactor for periods of about eight days. There, the uranium fissions into molybdenum-99 when struck by neutrons. After irradiation, the target is quickly processed to isolate the molybdenum-99, which is shipped to customers in a container that allows them to remove technetium-99m as it is formed.

Because high-grade uranium can also be used in nuclear weapons, the Obama administration and its predecessor have sought approaches that make use of low-grade uranium, which cannot.

Commercial nuclear reactors cannot generally be used to produce the isotope because they are sealed, so that targets cannot be inserted and removed.

GE Hitachi Nuclear Energy said last month, however, that some of its commercial reactors could potentially be used because they have a small opening that allows technicians to insert a probe to measure neutron flux inside the core.

The company is now performing experiments in which a low-grade uranium target is inserted instead of the probe to produce molybdenum. The company received $2.25 million in stimulus funds to develop the procedure and is using a similar amount of its own funds to develop the process, it said.

Reactor manufacturer Babcock & Wilcox has received $9 million in stimulus funds to develop a tiny reactor that is fueled by uranium in a liquid form. After the reactor has operated for a few days, the liquid would be drained into a container whose shape prevents a chain reaction from continuing. Once the molybdenum is removed, the uranium would be inserted back into the reactor.

Such a reactor could not be available for another two or three years at least.

Nuclear officials are also exploring ways to produce molybdenum-99 at a research reactor at the University of Missouri. That may be the best hope for near-term increases in supply, but it is not clear how soon product from there could be available.

thomas.maugh@latimes.com

Copyright (c) 2010, The Los Angeles Times

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New Source of an Isotope in Medicine Is Found
By MATTHEW L. WALD
Published: February 16, 2010
http://www.nytimes.com/2010/02/17/health/17isotope.html

WASHINGTON ― Just as the worldwide shortage of a radioactive isotope used in millions of medical procedures is about to get worse, officials say a new source for the substance has emerged: a nuclear reactor in Poland.

The isotope, technetium 99, is used to measure blood flow in the heart and to help diagnose bone and breast cancers. Almost two-thirds of the world’s supply comes from two reactors; one, in Ontario, has been shut for repairs for nine months and is not expected to reopen before April, and the other, in the Netherlands, will close for six months starting Friday.

Radiologists say that as a result of the shortage, their treatment of some patients has had to revert to inferior materials and techniques they stopped using 20 years ago.

But on Wednesday, Covidien, a company in St. Louis that purifies the material created in the reactor and packages it in a form usable by radiologists, will announce that it has signed a contract with the operators of the Maria reactor, near Warsaw, one of the world’s most powerful research reactors.

The Maria, a 36-year-old reactor, will fill only a small fraction of the gap left by the shutdowns at Chalk River, Ontario, and Petten, the Netherlands. Still, Dr. Michael M. Graham, a professor of radiology at the University of Iowa and a member of the board of the Society of Nuclear Medicine, said the new arrangement “could make the difference between being able to limp along and shutting down.”

As the American base of reactors for research and isotope production withers, the United States has increasingly looked abroad for radioactive materials. The inspector general of the Energy Department has reported that supplies have sometimes been unreliable, either late or not meeting specifications.

But people involved in the transaction said Poland had recently made substantial investments in the Maria reactor, named for the pioneering physicist Marie Sklodowska Curie.

Transferring enriched uranium to a former member of the Soviet bloc and bringing the material back to the Netherlands for processing required 20 permits from five countries, said Stephen E. Littlejohn, a spokesman for Covidien. But the regulatory work is not complete; the Food and Drug Administration will not give permission for the isotope to be used on patients in this country until it has reviewed samples from the new source, Mr. Littlejohn said.

The announcement of the new source for technetium 99 will come amid a flurry of activity around the United States to find new, more reliable ways to make the isotope and to avoid the use of bomb-grade uranium in the process.

General Electric has a plan to make technetium 99 using neutrons from power reactors owned by utilities, a neat trick because those reactors are usually sealed up and run for months at a time, while the medical isotope has to be removed within a few hours of its creation or it decays away. Babcock & Wilcox, a Virginia company that provides a variety of nuclear services, has a plan for a liquid-fueled reactor.

The National Nuclear Security Administration, the Energy Department agency that tries to reduce proliferation, recently said it would help finance both efforts; others are in the works, Obama administration officials say.

The isotope, known as tech 99m, is a product of the rapid decay of another radioactive isotope, molybdenum 99, which is itself produced by splitting atoms of uranium 235. Tech 99m is valued because it emits a gamma ray that is easy to spot in the patient’s body.

But it, too, decays quickly, so doctors have taken to scheduling procedures late at night and on weekends to make use of material that would otherwise vanish.

Andrzej Strupczewski, chairman of the nuclear safety commission in the Polish Institute of Atomic Energy, said it would be tricky to produce technetium at the Maria reactor because it lacked forced-air systems to cool the uranium that is split to make molybdenum 99. But a recent test went well, he said.

No one seems quite sure whether other reactors can be found to produce the medical isotope. Tammy P. Taylor, a senior policy analyst at the White House Office of Science and Technology Policy, said that while two-thirds of the world’s supply came from Petten and Chalk River, “historically, that’s more at contractual limits than production and safety limits.”

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